From 998fb29c46bcde3490f4036649c8655103ecbd84 Mon Sep 17 00:00:00 2001
From: swithek <52840391+swithek@users.noreply.github.com>
Date: Sat, 26 Sep 2026 20:02:48 +0200
Subject: [PATCH] add diff popover

---
 web/AGENTS.md                                 |   7 +
 web/app/components/editor/attribute-names.ts  |   3 +
 .../editor/blocks/figma/FigmaBlock.vue        |   9 +-
 .../figma/FigmaDiffDetails.nuxt.test.ts       |  69 ++++++
 .../editor/blocks/figma/FigmaDiffDetails.vue  |  94 +++++++
 .../editor/blocks/file/FileBlock.nuxt.test.ts |  10 +-
 .../editor/blocks/file/FileBlock.vue          |  19 +-
 .../blocks/file/FileDiffDetails.nuxt.test.ts  |  67 +++++
 .../editor/blocks/file/FileDiffDetails.vue    |  64 +++++
 .../editor/blocks/image/ImageBlock.vue        |   9 +-
 .../image/ImageDiffDetails.nuxt.test.ts       |  82 +++++++
 .../editor/blocks/image/ImageDiffDetails.vue  |  57 +++++
 .../editor/blocks/mermaid/MainBlock.vue       |   5 +-
 .../mermaid/MermaidDiffDetails.nuxt.test.ts   |  94 +++++++
 .../blocks/mermaid/MermaidDiffDetails.vue     |  75 ++++++
 .../editor/blocks/mermaid/diff-lines.test.ts  | 137 +++++++++++
 .../editor/blocks/mermaid/diff-lines.ts       |  89 +++++++
 .../editor/blocks/metrics/MainBlock.vue       |   5 +-
 .../metrics/MetricDiffDetails.nuxt.test.ts    | 200 +++++++++++++++
 .../blocks/metrics/MetricDiffDetails.vue      | 161 ++++++++++++
 .../editor/diff/DiffBeforeAfter.nuxt.test.ts  |  52 ++++
 .../editor/diff/DiffBeforeAfter.vue           |  48 ++++
 .../editor/diff/DiffChangeMarker.nuxt.test.ts |  92 ++++++-
 .../editor/diff/DiffChangeMarker.vue          |  73 ++++--
 .../editor/diff/DiffFieldChanges.nuxt.test.ts |  65 +++++
 .../editor/diff/DiffFieldChanges.vue          |  44 ++++
 .../editor/diff/change-count.test.ts          | 173 ++++++++++++-
 .../components/editor/diff/change-count.ts    | 230 ++++++++++++------
 web/i18n/locales/en/editor.json               |  25 +-
 29 files changed, 1935 insertions(+), 123 deletions(-)
 create mode 100644 web/app/components/editor/blocks/figma/FigmaDiffDetails.nuxt.test.ts
 create mode 100644 web/app/components/editor/blocks/figma/FigmaDiffDetails.vue
 create mode 100644 web/app/components/editor/blocks/file/FileDiffDetails.nuxt.test.ts
 create mode 100644 web/app/components/editor/blocks/file/FileDiffDetails.vue
 create mode 100644 web/app/components/editor/blocks/image/ImageDiffDetails.nuxt.test.ts
 create mode 100644 web/app/components/editor/blocks/image/ImageDiffDetails.vue
 create mode 100644 web/app/components/editor/blocks/mermaid/MermaidDiffDetails.nuxt.test.ts
 create mode 100644 web/app/components/editor/blocks/mermaid/MermaidDiffDetails.vue
 create mode 100644 web/app/components/editor/blocks/mermaid/diff-lines.test.ts
 create mode 100644 web/app/components/editor/blocks/mermaid/diff-lines.ts
 create mode 100644 web/app/components/editor/blocks/metrics/MetricDiffDetails.nuxt.test.ts
 create mode 100644 web/app/components/editor/blocks/metrics/MetricDiffDetails.vue
 create mode 100644 web/app/components/editor/diff/DiffBeforeAfter.nuxt.test.ts
 create mode 100644 web/app/components/editor/diff/DiffBeforeAfter.vue
 create mode 100644 web/app/components/editor/diff/DiffFieldChanges.nuxt.test.ts
 create mode 100644 web/app/components/editor/diff/DiffFieldChanges.vue

diff --git a/web/AGENTS.md b/web/AGENTS.md
index 193ddc14..6d1a378d 100644
--- a/web/AGENTS.md
+++ b/web/AGENTS.md
@@ -93,6 +93,13 @@ there when none exists.
   (custom nodes; `upload-handler.ts` routes dropped files), `comments/`,
   `diff/`, `drag-handle/`, `slash/`, `link/`, `ai/`, `hooks/`. Editor-wide
   state is [app/stores/editor.ts](app/stores/editor.ts).
+- **Diff view**: adding or changing a block or node includes its branch
+  diff. Expose `diffStatus` on its node view and style it as added, removed
+  and modified. A block changed through its attributes renders
+  `DiffChangeMarker` with a `<Block>DiffDetails.vue` card in its own
+  directory. Attributes that count as one change, count per list item or
+  are never set by a user are declared in
+  [diff/change-count.ts](app/components/editor/diff/change-count.ts).
 - **Routing**: one dynamic page,
   `app/pages/[[organizationSlug]]/[[documentSlug]].vue`;
   [app/middleware/01.redirect.global.ts](app/middleware/01.redirect.global.ts)
diff --git a/web/app/components/editor/attribute-names.ts b/web/app/components/editor/attribute-names.ts
index 476c8d82..1e58966b 100644
--- a/web/app/components/editor/attribute-names.ts
+++ b/web/app/components/editor/attribute-names.ts
@@ -2,3 +2,6 @@
 // editor modules
 
 export const NODE_COMMENT_ID_ATTR = "nodeCommentId"
+
+// set on image and file blocks while their upload is in flight
+export const UPLOADING_ATTR = "uploading"
diff --git a/web/app/components/editor/blocks/figma/FigmaBlock.vue b/web/app/components/editor/blocks/figma/FigmaBlock.vue
index 3f7be025..f703bb54 100644
--- a/web/app/components/editor/blocks/figma/FigmaBlock.vue
+++ b/web/app/components/editor/blocks/figma/FigmaBlock.vue
@@ -4,6 +4,7 @@ import { computePosition, flip, offset, shift } from "@floating-ui/dom"
 import { cn } from "~/lib/utils"
 import { DiffStatus } from "~/components/editor/diff/position-map"
 import DiffChangeMarker from "~/components/editor/diff/DiffChangeMarker.vue"
+import FigmaDiffDetails from "./FigmaDiffDetails.vue"
 import { isFigmaUrl, convertToEmbedUrl } from "./index"
 
 const props = defineProps(nodeViewProps)
@@ -262,7 +263,9 @@ onBeforeUnmount(() => {
 				:style="{ height: `${displayHeight}px` }"
 				allowfullscreen
 			/>
-			<DiffChangeMarker :node="props.node" class="absolute top-1.5 right-1.5" />
+			<DiffChangeMarker :node="props.node" class="absolute top-1.5 right-1.5">
+				<FigmaDiffDetails :node="props.node" />
+			</DiffChangeMarker>
 			<div
 				v-if="!isEditingDisabled"
 				aria-hidden="true"
@@ -295,7 +298,9 @@ onBeforeUnmount(() => {
 			<DiffChangeMarker
 				:node="props.node"
 				class="absolute top-1/2 right-2 -translate-y-1/2"
-			/>
+			>
+				<FigmaDiffDetails :node="props.node" />
+			</DiffChangeMarker>
 			<span class="mt-0.25 text-2sm text-muted-foreground">
 				{{
 					isEditingDisabled
diff --git a/web/app/components/editor/blocks/figma/FigmaDiffDetails.nuxt.test.ts b/web/app/components/editor/blocks/figma/FigmaDiffDetails.nuxt.test.ts
new file mode 100644
index 00000000..a845fb55
--- /dev/null
+++ b/web/app/components/editor/blocks/figma/FigmaDiffDetails.nuxt.test.ts
@@ -0,0 +1,69 @@
+import { mountSuspended } from "@nuxt/test-utils/runtime"
+import { describe, it } from "vitest"
+import FigmaDiffDetails from "./FigmaDiffDetails.vue"
+import { makeNode } from "../../test-helpers/node-view"
+import { DiffStatus } from "~/components/editor/diff/position-map"
+import { t } from "~/components/test-helpers"
+
+const OLD_URL = "https://www.figma.com/design/abc123/Checkout-Flow"
+const NEW_URL = "https://www.figma.com/design/xyz789/Sign%20up-Screen"
+
+describe("<FigmaDiffDetails>", () => {
+	it("names the old and the new file from their URLs", async ({ expect }) => {
+		const wrapper = await mountDetails({ src: OLD_URL }, { src: NEW_URL })
+
+		expect(wrapper.findAll(".font-medium").map((name) => name.text())).toEqual([
+			"Checkout Flow",
+			"Sign up Screen",
+		])
+		expect(wrapper.text()).toContain(OLD_URL)
+	})
+
+	it("keeps the raw text of a URL it cannot parse", async ({ expect }) => {
+		const wrapper = await mountDetails({}, { src: "not a url" })
+
+		expect(wrapper.get(".font-medium").text()).toBe("not a url")
+		expect(wrapper.text()).toContain(t("editor.figma.empty"))
+	})
+
+	it("shows auto for a size that was not set before", async ({ expect }) => {
+		const wrapper = await mountDetails(
+			{ src: OLD_URL },
+			{ src: OLD_URL, height: 300 },
+		)
+
+		expect(wrapper.get(".line-through").text()).toBe(
+			t("editor.diff-change-marker.auto"),
+		)
+		expect(wrapper.get(".bg-diff-text-added").text()).toBe(
+			t("editor.diff-change-marker.pixels", { value: "300" }),
+		)
+	})
+
+	it("lists a resize as rows", async ({ expect }) => {
+		const wrapper = await mountDetails(
+			{ src: OLD_URL, width: 400, height: 300 },
+			{ src: OLD_URL, width: 600, height: 300 },
+		)
+
+		expect(wrapper.findAll("dt").map((dt) => dt.text())).toEqual([
+			t("editor.figma.diff.width"),
+		])
+		expect(wrapper.find(".font-medium").exists()).toBe(false)
+	})
+})
+
+function mountDetails(
+	oldAttrs: Record<string, unknown>,
+	newAttrs: Record<string, unknown>,
+) {
+	return mountSuspended(FigmaDiffDetails, {
+		props: {
+			node: makeNode({
+				...newAttrs,
+				diffStatus: DiffStatus.Modified,
+				oldNode: { attrs: oldAttrs },
+			}),
+		},
+	})
+}
diff --git a/web/app/components/editor/blocks/figma/FigmaDiffDetails.vue b/web/app/components/editor/blocks/figma/FigmaDiffDetails.vue
new file mode 100644
index 00000000..d1fe186b
--- /dev/null
+++ b/web/app/components/editor/blocks/figma/FigmaDiffDetails.vue
@@ -0,0 +1,94 @@
+<script lang="ts" setup>
+import type { Node as PMNode } from "@tiptap/pm/model"
+import {
+	collectAttributeChanges,
+	displayValue,
+	formatChange,
+	type FieldChange,
+} from "~/components/editor/diff/change-count"
+import DiffBeforeAfter from "~/components/editor/diff/DiffBeforeAfter.vue"
+import DiffFieldChanges from "~/components/editor/diff/DiffFieldChanges.vue"
+
+const props = defineProps<{
+	node: PMNode
+}>()
+
+const { t } = useI18n({ useScope: "global" })
+
+const changes = computed(() => collectAttributeChanges(props.node))
+const srcChange = computed(() =>
+	changes.value.find((change) => change.name === "src"),
+)
+const rows = computed<FieldChange[]>(() => {
+	const labels: Record<string, string> = {
+		width: t("editor.figma.diff.width"),
+		height: t("editor.figma.diff.height"),
+	}
+
+	return changes.value.flatMap((change) => {
+		const label = labels[change.name]
+
+		return label
+			? [
+					{
+						label: label,
+						...formatChange(
+							change,
+							pixels,
+							t("editor.diff-change-marker.auto"),
+						),
+					},
+				]
+			: []
+	})
+})
+
+function pixels(value: unknown): string {
+	return t("editor.diff-change-marker.pixels", { value: displayValue(value) })
+}
+
+// a figma URL ends in a slug of the file's name, such as
+// /design/<key>/Checkout-Flow. The raw URL stands in when it has none.
+function describe(src: unknown) {
+	if (typeof src !== "string") {
+		return undefined
+	}
+
+	let name = src
+	try {
+		const slug = new URL(src).pathname.split("/").filter(Boolean)[2]
+		if (slug) {
+			name = decodeURIComponent(slug).replaceAll("-", " ")
+		}
+	} catch {
+		// an unparsable URL keeps its raw text as the name
+	}
+
+	return { name: name, src: src }
+}
+</script>
+
+<template>
+	<div class="flex w-80 flex-col gap-3">
+		<DiffBeforeAfter
+			v-if="srcChange"
+			v-slot="{ value }"
+			:before="describe(srcChange.oldValue)"
+			:after="describe(srcChange.newValue)"
+			:empty-label="t('editor.figma.empty')"
+		>
+			<div class="flex w-full min-w-0 items-center gap-2 p-2">
+				<Icon name="simple-icons:figma" class="size-4 shrink-0" />
+				<span class="flex min-w-0 flex-col">
+					<span class="line-clamp-6 text-xs font-medium break-words">
+						{{ value.name }}
+					</span>
+					<span class="truncate text-xs text-muted-foreground">
+						{{ value.src }}
+					</span>
+				</span>
+			</div>
+		</DiffBeforeAfter>
+		<DiffFieldChanges v-if="rows.length" :rows="rows" />
+	</div>
+</template>
diff --git a/web/app/components/editor/blocks/file/FileBlock.nuxt.test.ts b/web/app/components/editor/blocks/file/FileBlock.nuxt.test.ts
index f213321f..f908502d 100644
--- a/web/app/components/editor/blocks/file/FileBlock.nuxt.test.ts
+++ b/web/app/components/editor/blocks/file/FileBlock.nuxt.test.ts
@@ -381,10 +381,14 @@ describe("<FileBlock>", { concurrent: false }, () => {
 			}),
 		)
 
+		const label = t("editor.diff-change-marker.label", {
+			removed: 1,
+			added: 1,
+		})
 		expect(wrapper.find(".diff-overlay").exists()).toBe(false)
-		expect(wrapper.text()).toContain(
-			t("editor.diff-change-marker.label", { removed: 1, added: 1 }),
-		)
+		expect(wrapper.text()).toContain(label)
+		// hovering a marker inside the card would set off the card's hover
+		expect(wrapper.get("a").text()).not.toContain(label)
 	})
 
 	it("shows no diff overlay on an unchanged file", async ({ expect }) => {
diff --git a/web/app/components/editor/blocks/file/FileBlock.vue b/web/app/components/editor/blocks/file/FileBlock.vue
index e27c598c..af97f9d7 100644
--- a/web/app/components/editor/blocks/file/FileBlock.vue
+++ b/web/app/components/editor/blocks/file/FileBlock.vue
@@ -6,6 +6,7 @@ import type { ProgressToast } from "~/components/toast"
 import { cn } from "~/lib/utils"
 import { DiffStatus } from "~/components/editor/diff/position-map"
 import DiffChangeMarker from "~/components/editor/diff/DiffChangeMarker.vue"
+import FileDiffDetails from "./FileDiffDetails.vue"
 import {
 	fileKind,
 	fileKindStyle,
@@ -175,7 +176,7 @@ async function downloadOnDesktop() {
 	<NodeViewWrapper
 		:id="props.node.attrs.uid"
 		as="figure"
-		class="not-prose flex caret-transparent"
+		class="not-prose relative flex caret-transparent"
 		data-type="fileBlock"
 		:data-uid="props.node.attrs.uid"
 		:data-node-comment-id="props.node.attrs.nodeCommentId"
@@ -233,10 +234,6 @@ async function downloadOnDesktop() {
 					{{ size }}
 				</span>
 			</span>
-			<DiffChangeMarker
-				:node="props.node"
-				class="absolute top-1/2 right-2 -translate-y-1/2"
-			/>
 		</component>
 		<button
 			v-else
@@ -252,10 +249,6 @@ async function downloadOnDesktop() {
 			@click="openFilePicker"
 		>
 			<Icon name="mingcute:attachment-line" class="size-4 text-foreground" />
-			<DiffChangeMarker
-				:node="props.node"
-				class="absolute top-1/2 right-2 -translate-y-1/2"
-			/>
 			<div class="mt-0.25 text-2sm text-muted-foreground">
 				{{
 					uploading
@@ -275,5 +268,13 @@ async function downloadOnDesktop() {
 				@change="handleFileChange"
 			/>
 		</button>
+		<!-- a sibling of the card rather than its child, so hovering the
+		marker does not trigger the card's hover style -->
+		<DiffChangeMarker
+			:node="props.node"
+			class="absolute top-1/2 right-2 -translate-y-1/2"
+		>
+			<FileDiffDetails :node="props.node" />
+		</DiffChangeMarker>
 	</NodeViewWrapper>
 </template>
diff --git a/web/app/components/editor/blocks/file/FileDiffDetails.nuxt.test.ts b/web/app/components/editor/blocks/file/FileDiffDetails.nuxt.test.ts
new file mode 100644
index 00000000..41efb0e2
--- /dev/null
+++ b/web/app/components/editor/blocks/file/FileDiffDetails.nuxt.test.ts
@@ -0,0 +1,67 @@
+import { mountSuspended } from "@nuxt/test-utils/runtime"
+import { describe, it } from "vitest"
+import FileDiffDetails from "./FileDiffDetails.vue"
+import { makeNode } from "../../test-helpers/node-view"
+import { FILE_BLOCK_NAME } from "../node-names"
+import { formatFileSize } from "./file-kind"
+import { DiffStatus } from "~/components/editor/diff/position-map"
+import { t } from "~/components/test-helpers"
+
+describe("<FileDiffDetails>", () => {
+	it("shows the old and the new file side by side", async ({ expect }) => {
+		const wrapper = await mountDetails(storedFile("a.zip"), storedFile("b.pdf"))
+
+		expect(wrapper.findAll(".font-medium").map((name) => name.text())).toEqual([
+			"a.zip",
+			"b.pdf",
+		])
+		expect(wrapper.text()).toContain(formatFileSize(1024))
+	})
+
+	it("shows an empty side for a newly uploaded file", async ({ expect }) => {
+		const wrapper = await mountDetails({}, storedFile("b.pdf"))
+
+		expect(wrapper.findAll(".font-medium").map((name) => name.text())).toEqual([
+			"b.pdf",
+		])
+		expect(wrapper.text()).toContain(t("editor.file.empty"))
+	})
+
+	it("renders nothing when the file itself is unchanged", async ({
+		expect,
+	}) => {
+		const wrapper = await mountDetails(
+			{ ...storedFile("a.zip"), uploading: true },
+			{ ...storedFile("a.zip"), uploading: false },
+		)
+
+		expect(wrapper.html()).toBe("<!--v-if-->")
+	})
+})
+
+function storedFile(name: string): Record<string, unknown> {
+	return {
+		src: `/files/${name}`,
+		name: name,
+		size: 1024,
+		contentType: "application/octet-stream",
+	}
+}
+
+function mountDetails(
+	oldAttrs: Record<string, unknown>,
+	newAttrs: Record<string, unknown>,
+) {
+	return mountSuspended(FileDiffDetails, {
+		props: {
+			node: makeNode(
+				{
+					...newAttrs,
+					diffStatus: DiffStatus.Modified,
+					oldNode: { attrs: oldAttrs },
+				},
+				{ typeName: FILE_BLOCK_NAME },
+			),
+		},
+	})
+}
diff --git a/web/app/components/editor/blocks/file/FileDiffDetails.vue b/web/app/components/editor/blocks/file/FileDiffDetails.vue
new file mode 100644
index 00000000..c5871d92
--- /dev/null
+++ b/web/app/components/editor/blocks/file/FileDiffDetails.vue
@@ -0,0 +1,64 @@
+<script lang="ts" setup>
+import type { Node as PMNode } from "@tiptap/pm/model"
+import { collectAttributeChanges } from "~/components/editor/diff/change-count"
+import DiffBeforeAfter from "~/components/editor/diff/DiffBeforeAfter.vue"
+import { fileKind, fileKindStyle, formatFileSize } from "./file-kind"
+
+interface StoredFile {
+	name?: string
+	size?: number
+	contentType?: string
+}
+
+const props = defineProps<{
+	node: PMNode
+}>()
+
+const { t } = useI18n({ useScope: "global" })
+
+// the file's attributes change together, so they arrive as one group
+const fileChange = computed(() =>
+	collectAttributeChanges(props.node).find((change) => change.name === "file"),
+)
+
+function describe(value: unknown) {
+	if (!value) {
+		return undefined
+	}
+
+	const file = value as StoredFile
+
+	return {
+		name: file.name ?? "",
+		size: formatFileSize(file.size),
+		icon: fileKindStyle(fileKind(file.name ?? "", file.contentType ?? "")).icon,
+	}
+}
+</script>
+
+<template>
+	<DiffBeforeAfter
+		v-if="fileChange"
+		v-slot="{ value }"
+		:before="describe(fileChange.oldValue)"
+		:after="describe(fileChange.newValue)"
+		:empty-label="t('editor.file.empty')"
+		class="w-80"
+	>
+		<div class="flex w-full min-w-0 items-center gap-2 p-2">
+			<span
+				class="flex size-7 shrink-0 items-center justify-center rounded-md bg-muted text-muted-foreground"
+			>
+				<Icon :name="value.icon" class="size-4" />
+			</span>
+			<span class="flex min-w-0 flex-col">
+				<span class="line-clamp-6 text-xs font-medium break-words">
+					{{ value.name }}
+				</span>
+				<span v-if="value.size" class="text-xs text-muted-foreground">
+					{{ value.size }}
+				</span>
+			</span>
+		</div>
+	</DiffBeforeAfter>
+</template>
diff --git a/web/app/components/editor/blocks/image/ImageBlock.vue b/web/app/components/editor/blocks/image/ImageBlock.vue
index 2081558c..212c456b 100644
--- a/web/app/components/editor/blocks/image/ImageBlock.vue
+++ b/web/app/components/editor/blocks/image/ImageBlock.vue
@@ -5,6 +5,7 @@ import { showToastMessage } from "~/components/toast"
 import { cn } from "~/lib/utils"
 import { DiffStatus } from "~/components/editor/diff/position-map"
 import DiffChangeMarker from "~/components/editor/diff/DiffChangeMarker.vue"
+import ImageDiffDetails from "./ImageDiffDetails.vue"
 
 const MIN_WIDTH = 128
 
@@ -248,7 +249,9 @@ onBeforeUnmount(() => {
 				]"
 				draggable="false"
 			/>
-			<DiffChangeMarker :node="props.node" class="absolute top-1.5 right-1.5" />
+			<DiffChangeMarker :node="props.node" class="absolute top-1.5 right-1.5">
+				<ImageDiffDetails :node="props.node" />
+			</DiffChangeMarker>
 			<div
 				v-if="showResizeHandle"
 				aria-hidden="true"
@@ -275,7 +278,9 @@ onBeforeUnmount(() => {
 			<DiffChangeMarker
 				:node="props.node"
 				class="absolute top-1/2 right-2 -translate-y-1/2"
-			/>
+			>
+				<ImageDiffDetails :node="props.node" />
+			</DiffChangeMarker>
 			<div class="mt-0.25 text-2sm text-muted-foreground">
 				{{
 					uploading
diff --git a/web/app/components/editor/blocks/image/ImageDiffDetails.nuxt.test.ts b/web/app/components/editor/blocks/image/ImageDiffDetails.nuxt.test.ts
new file mode 100644
index 00000000..849a0d5d
--- /dev/null
+++ b/web/app/components/editor/blocks/image/ImageDiffDetails.nuxt.test.ts
@@ -0,0 +1,82 @@
+import { mountSuspended } from "@nuxt/test-utils/runtime"
+import { describe, it } from "vitest"
+import ImageDiffDetails from "./ImageDiffDetails.vue"
+import { makeNode } from "../../test-helpers/node-view"
+import { IMAGE_BLOCK_NAME } from "../node-names"
+import { DiffStatus } from "~/components/editor/diff/position-map"
+import { t } from "~/components/test-helpers"
+
+describe("<ImageDiffDetails>", () => {
+	it("shows the old and the new image side by side", async ({ expect }) => {
+		const wrapper = await mountDetails({ src: "a.png" }, { src: "b.png" })
+
+		expect(wrapper.findAll("img").map((img) => img.attributes("src"))).toEqual([
+			"a.png",
+			"b.png",
+		])
+	})
+
+	it("shows an empty side for a newly uploaded image", async ({ expect }) => {
+		const wrapper = await mountDetails({}, { src: "b.png" })
+
+		expect(wrapper.findAll("img").map((img) => img.attributes("src"))).toEqual([
+			"b.png",
+		])
+		expect(wrapper.text()).toContain(t("editor.image.empty"))
+	})
+
+	it("lists a resize as a row", async ({ expect }) => {
+		const wrapper = await mountDetails(
+			{ src: "a.png", width: 300 },
+			{ src: "a.png", width: 480 },
+		)
+
+		expect(wrapper.get("dt").text()).toBe(t("editor.image.diff.width"))
+		expect(wrapper.get(".line-through").text()).toBe(
+			t("editor.diff-change-marker.pixels", { value: "300" }),
+		)
+		expect(wrapper.get(".bg-diff-text-added").text()).toBe(
+			t("editor.diff-change-marker.pixels", { value: "480" }),
+		)
+		expect(wrapper.find("img").exists()).toBe(false)
+	})
+
+	it("shows auto for a width that was not set before", async ({ expect }) => {
+		const wrapper = await mountDetails({}, { src: "b.png", width: 492 })
+
+		expect(wrapper.get(".line-through").text()).toBe(
+			t("editor.diff-change-marker.auto"),
+		)
+		expect(wrapper.get(".bg-diff-text-added").text()).toBe(
+			t("editor.diff-change-marker.pixels", { value: "492" }),
+		)
+	})
+
+	it("shows nothing for attributes no one can change", async ({ expect }) => {
+		const wrapper = await mountDetails(
+			{ src: "a.png", alt: "a cat", uploading: true },
+			{ src: "a.png", alt: "a dog", uploading: false },
+		)
+
+		expect(wrapper.find("dl").exists()).toBe(false)
+		expect(wrapper.find("img").exists()).toBe(false)
+	})
+})
+
+function mountDetails(
+	oldAttrs: Record<string, unknown>,
+	newAttrs: Record<string, unknown>,
+) {
+	return mountSuspended(ImageDiffDetails, {
+		props: {
+			node: makeNode(
+				{
+					...newAttrs,
+					diffStatus: DiffStatus.Modified,
+					oldNode: { attrs: oldAttrs },
+				},
+				{ typeName: IMAGE_BLOCK_NAME },
+			),
+		},
+	})
+}
diff --git a/web/app/components/editor/blocks/image/ImageDiffDetails.vue b/web/app/components/editor/blocks/image/ImageDiffDetails.vue
new file mode 100644
index 00000000..7ccbebfa
--- /dev/null
+++ b/web/app/components/editor/blocks/image/ImageDiffDetails.vue
@@ -0,0 +1,57 @@
+<script lang="ts" setup>
+import type { Node as PMNode } from "@tiptap/pm/model"
+import {
+	collectAttributeChanges,
+	displayValue,
+	formatChange,
+	type FieldChange,
+} from "~/components/editor/diff/change-count"
+import DiffBeforeAfter from "~/components/editor/diff/DiffBeforeAfter.vue"
+import DiffFieldChanges from "~/components/editor/diff/DiffFieldChanges.vue"
+
+const props = defineProps<{
+	node: PMNode
+}>()
+
+const { t } = useI18n({ useScope: "global" })
+
+const changes = computed(() => collectAttributeChanges(props.node))
+const srcChange = computed(() =>
+	changes.value.find((change) => change.name === "src"),
+)
+const rows = computed<FieldChange[]>(() =>
+	changes.value
+		.filter((change) => change.name === "width")
+		.map((change) => ({
+			label: t("editor.image.diff.width"),
+			...formatChange(change, pixels, t("editor.diff-change-marker.auto")),
+		})),
+)
+
+function pixels(value: unknown): string {
+	return t("editor.diff-change-marker.pixels", { value: displayValue(value) })
+}
+
+function imageSrc(value: unknown): string | undefined {
+	return typeof value === "string" ? value : undefined
+}
+</script>
+
+<template>
+	<div class="flex w-72 flex-col gap-3">
+		<DiffBeforeAfter
+			v-if="srcChange"
+			v-slot="{ value }"
+			:before="imageSrc(srcChange.oldValue)"
+			:after="imageSrc(srcChange.newValue)"
+			:empty-label="t('editor.image.empty')"
+		>
+			<img
+				:src="value"
+				:alt="t('editor.image.diff.image')"
+				class="h-20 w-full object-cover"
+			/>
+		</DiffBeforeAfter>
+		<DiffFieldChanges v-if="rows.length" :rows="rows" />
+	</div>
+</template>
diff --git a/web/app/components/editor/blocks/mermaid/MainBlock.vue b/web/app/components/editor/blocks/mermaid/MainBlock.vue
index 45e34ee7..f56926f5 100644
--- a/web/app/components/editor/blocks/mermaid/MainBlock.vue
+++ b/web/app/components/editor/blocks/mermaid/MainBlock.vue
@@ -4,6 +4,7 @@ import { cn } from "~/lib/utils"
 import { explicitContentPlaceholder } from "../../placeholder"
 import { DiffStatus } from "../../diff/position-map"
 import DiffChangeMarker from "../../diff/DiffChangeMarker.vue"
+import MermaidDiffDetails from "./MermaidDiffDetails.vue"
 import MermaidPreview from "./MermaidPreview.vue"
 
 const props = defineProps(nodeViewProps)
@@ -119,7 +120,9 @@ watch(showCode, () => {
 			{{ lastOtherEditingUser?.name }}
 		</div>
 		<div class="absolute top-1 right-1.5 z-1 flex items-center gap-1">
-			<DiffChangeMarker :node="props.node" />
+			<DiffChangeMarker :node="props.node">
+				<MermaidDiffDetails :node="props.node" />
+			</DiffChangeMarker>
 			<ShadcnUiButton
 				variant="ghost-plain"
 				size="icon-sm"
diff --git a/web/app/components/editor/blocks/mermaid/MermaidDiffDetails.nuxt.test.ts b/web/app/components/editor/blocks/mermaid/MermaidDiffDetails.nuxt.test.ts
new file mode 100644
index 00000000..fa13a744
--- /dev/null
+++ b/web/app/components/editor/blocks/mermaid/MermaidDiffDetails.nuxt.test.ts
@@ -0,0 +1,94 @@
+import { mountSuspended } from "@nuxt/test-utils/runtime"
+import { Schema, type Node as PMNode } from "@tiptap/pm/model"
+import { describe, it } from "vitest"
+import MermaidDiffDetails from "./MermaidDiffDetails.vue"
+import {
+	DIFF_TEXT_ADDED_MARK_NAME,
+	DIFF_TEXT_REMOVED_MARK_NAME,
+} from "~/components/editor/mark-names"
+import { t } from "~/components/test-helpers"
+
+const ADDED = DIFF_TEXT_ADDED_MARK_NAME
+const REMOVED = DIFF_TEXT_REMOVED_MARK_NAME
+
+const schema = new Schema({
+	nodes: {
+		doc: { content: "code" },
+		code: { content: "text*", marks: "_" },
+		text: {},
+	},
+	marks: {
+		[ADDED]: {},
+		[REMOVED]: {},
+	},
+})
+
+describe("<MermaidDiffDetails>", () => {
+	it("shows only the changed lines, numbered, with their changes marked", async ({
+		expect,
+	}) => {
+		const wrapper = await mountDetails([
+			["graph TD\nA-->"],
+			["B", REMOVED],
+			["C", ADDED],
+			["\nC-->D"],
+		])
+
+		expect(numbers(wrapper)).toEqual(["2"])
+		// the raw text content, since text() would trim a stray space away
+		expect(wrapper.get(".break-all").element.textContent).toBe("A-->BC")
+		expect(wrapper.get(".line-through").text()).toBe("B")
+		expect(wrapper.get(".bg-diff-text-added").text()).toBe("C")
+	})
+
+	it("strips the indentation the shown lines share", async ({ expect }) => {
+		const wrapper = await mountDetails([
+			["flowchart TD\n    A-->"],
+			["B", REMOVED],
+			["C", ADDED],
+		])
+
+		expect(wrapper.get(".break-all").element.textContent).toBe("A-->BC")
+	})
+
+	it("separates changed lines that are not neighbours", async ({ expect }) => {
+		const wrapper = await mountDetails([
+			["one\n"],
+			["two", ADDED],
+			["\nthree\n"],
+			["four", ADDED],
+		])
+
+		expect(numbers(wrapper)).toEqual(["2", "4"])
+		expect(wrapper.findAll(".border-dashed")).toHaveLength(1)
+	})
+
+	it("counts the changed lines it leaves out", async ({ expect }) => {
+		const wrapper = await mountDetails(
+			Array.from({ length: 12 }, (_, index) => [`\nline ${index}`, ADDED]),
+		)
+
+		expect(numbers(wrapper)).toHaveLength(10)
+		expect(wrapper.text()).toContain(
+			t("editor.mermaid.diff.more-lines", { count: 3 }),
+		)
+	})
+})
+
+function numbers(wrapper: Awaited<ReturnType<typeof mountDetails>>) {
+	return wrapper.findAll(".select-none").map((cell) => cell.text())
+}
+
+function mountDetails(parts: string[][]) {
+	const node: PMNode = schema.nodes.code.create(
+		null,
+		parts.map(([text, ...marks]) =>
+			schema.text(
+				text ?? "",
+				marks.map((mark) => schema.mark(mark)),
+			),
+		),
+	)
+
+	return mountSuspended(MermaidDiffDetails, { props: { node: node } })
+}
diff --git a/web/app/components/editor/blocks/mermaid/MermaidDiffDetails.vue b/web/app/components/editor/blocks/mermaid/MermaidDiffDetails.vue
new file mode 100644
index 00000000..6ff02049
--- /dev/null
+++ b/web/app/components/editor/blocks/mermaid/MermaidDiffDetails.vue
@@ -0,0 +1,75 @@
+<script lang="ts" setup>
+import type { Node as PMNode } from "@tiptap/pm/model"
+import { cn } from "~/lib/utils"
+import {
+	TextSegmentKind,
+	textSegments,
+} from "~/components/editor/diff/change-count"
+import { dedentLines, diffLines } from "./diff-lines"
+
+const MAX_LINES = 10
+
+const props = defineProps<{
+	node: PMNode
+}>()
+
+const changedLines = computed(() =>
+	diffLines(textSegments(props.node))
+		.map((line, index) => ({ ...line, index: index }))
+		.filter((line) => line.changed),
+)
+const shownLines = computed(() =>
+	dedentLines(changedLines.value.slice(0, MAX_LINES)).map(
+		(line, position, shown) => ({
+			...line,
+			// a gap sits between two changed lines that are not neighbours
+			gapBefore:
+				position > 0 && line.index - (shown[position - 1]?.index ?? 0) > 1,
+		}),
+	),
+)
+const hiddenCount = computed(() =>
+	Math.max(changedLines.value.length - MAX_LINES, 0),
+)
+</script>
+
+<template>
+	<div class="flex max-w-[26rem] flex-col gap-1.5">
+		<!-- the number column is as wide as its widest number -->
+		<div
+			class="grid grid-cols-[max-content_minmax(0,1fr)] gap-x-1.5 gap-y-1.5 font-mono text-xs"
+		>
+			<template v-for="line in shownLines" :key="line.index">
+				<!-- the negative margin reaches the popover's padding, so the
+				separator runs from one edge of the card to the other -->
+				<hr
+					v-if="line.gapBefore"
+					class="col-span-2 -mx-3 my-1.5 border-t border-dashed border-border"
+				/>
+				<span class="text-muted-foreground select-none">
+					{{ line.number }}
+				</span>
+				<!-- only the segments keep their whitespace, so the template's own
+				line breaks around them do not show as spaces -->
+				<span class="break-all">
+					<span
+						v-for="(segment, i) in line.segments"
+						:key="i"
+						:class="
+							cn(
+								'whitespace-pre-wrap',
+								segment.kind === TextSegmentKind.Removed &&
+									'bg-diff-text-removed line-through',
+								segment.kind === TextSegmentKind.Added && 'bg-diff-text-added',
+							)
+						"
+						v-text="segment.text"
+					/>
+				</span>
+			</template>
+		</div>
+		<span v-if="hiddenCount" class="text-xs text-muted-foreground">
+			{{ $t("editor.mermaid.diff.more-lines", { count: hiddenCount }) }}
+		</span>
+	</div>
+</template>
diff --git a/web/app/components/editor/blocks/mermaid/diff-lines.test.ts b/web/app/components/editor/blocks/mermaid/diff-lines.test.ts
new file mode 100644
index 00000000..c226c71e
--- /dev/null
+++ b/web/app/components/editor/blocks/mermaid/diff-lines.test.ts
@@ -0,0 +1,137 @@
+import { describe, it } from "vitest"
+import { dedentLines, diffLines } from "./diff-lines"
+import { TextSegmentKind } from "~/components/editor/diff/change-count"
+
+const { Equal, Removed, Added } = TextSegmentKind
+
+describe("diffLines", () => {
+	it("splits segments into numbered lines and flags the changed ones", ({
+		expect,
+	}) => {
+		const lines = diffLines([
+			{ kind: Equal, text: "graph TD\nA-->" },
+			{ kind: Removed, text: "B" },
+			{ kind: Added, text: "C" },
+			{ kind: Equal, text: "\nC-->D" },
+		])
+
+		expect(lines).toEqual([
+			{
+				number: 1,
+				changed: false,
+				segments: [{ kind: Equal, text: "graph TD" }],
+			},
+			{
+				number: 2,
+				changed: true,
+				segments: [
+					{ kind: Equal, text: "A-->" },
+					{ kind: Removed, text: "B" },
+					{ kind: Added, text: "C" },
+				],
+			},
+			{ number: 3, changed: false, segments: [{ kind: Equal, text: "C-->D" }] },
+		])
+	})
+
+	it("leaves a line of only removed text unnumbered", ({ expect }) => {
+		const lines = diffLines([
+			{ kind: Equal, text: "graph TD" },
+			{ kind: Removed, text: "\nA-->B" },
+			{ kind: Equal, text: "\nB-->C" },
+		])
+
+		expect(lines.map((line) => [line.number, line.changed])).toEqual([
+			[1, true],
+			[null, true],
+			[2, false],
+		])
+	})
+
+	it("numbers an added line by its place in the new text", ({ expect }) => {
+		const lines = diffLines([
+			{ kind: Equal, text: "graph TD" },
+			{ kind: Added, text: "\nA-->B" },
+		])
+
+		expect(lines.map((line) => [line.number, line.changed])).toEqual([
+			[1, true],
+			[2, true],
+		])
+	})
+
+	it("flags the line whose newline was removed", ({ expect }) => {
+		const lines = diffLines([
+			{ kind: Equal, text: "A-->B" },
+			{ kind: Removed, text: "\n" },
+			{ kind: Equal, text: "B-->C" },
+		])
+
+		expect(lines.map((line) => [line.number, line.changed])).toEqual([
+			[1, true],
+			[1, false],
+		])
+	})
+})
+
+describe("dedentLines", () => {
+	it("strips the indentation every line shares", ({ expect }) => {
+		const lines = dedentLines(
+			diffLines([
+				{ kind: Equal, text: "    B-->" },
+				{ kind: Removed, text: "C" },
+				{ kind: Equal, text: "\n      D-->" },
+				{ kind: Added, text: "E" },
+			]),
+		)
+
+		expect(lines.map((line) => line.segments)).toEqual([
+			[
+				{ kind: Equal, text: "B-->" },
+				{ kind: Removed, text: "C" },
+			],
+			[
+				{ kind: Equal, text: "  D-->" },
+				{ kind: Added, text: "E" },
+			],
+		])
+	})
+
+	it("keeps an indent that is itself a change", ({ expect }) => {
+		const lines = diffLines([
+			{ kind: Equal, text: "    B-->C\n" },
+			{ kind: Added, text: "    D-->E" },
+		])
+
+		expect(dedentLines(lines)).toEqual(lines)
+	})
+
+	it("ignores empty lines when finding the shared indent", ({ expect }) => {
+		const lines = dedentLines(
+			diffLines([
+				{ kind: Equal, text: "    A" },
+				{ kind: Added, text: "\n" },
+				{ kind: Equal, text: "\n    B" },
+			]),
+		)
+
+		expect(lines.map((line) => line.segments)).toEqual([
+			[{ kind: Equal, text: "A" }],
+			[],
+			[{ kind: Equal, text: "B" }],
+		])
+	})
+
+	it("drops a segment that was only indentation", ({ expect }) => {
+		const lines = dedentLines(
+			diffLines([
+				{ kind: Equal, text: "  " },
+				{ kind: Added, text: "A" },
+			]),
+		)
+
+		expect(lines.map((line) => line.segments)).toEqual([
+			[{ kind: Added, text: "A" }],
+		])
+	})
+})
diff --git a/web/app/components/editor/blocks/mermaid/diff-lines.ts b/web/app/components/editor/blocks/mermaid/diff-lines.ts
new file mode 100644
index 00000000..b8f42507
--- /dev/null
+++ b/web/app/components/editor/blocks/mermaid/diff-lines.ts
@@ -0,0 +1,89 @@
+import {
+	TextSegmentKind,
+	type TextSegment,
+} from "~/components/editor/diff/change-count"
+
+const INDENT_RE = /^[ \t]*/
+
+export interface DiffLine {
+	// the line's number in the new text. Null for a line that holds only
+	// removed text, since the new text has no such line.
+	number: number | null
+	segments: TextSegment[]
+	changed: boolean
+}
+
+// split the segments of a diffed text into lines. A newline inside removed
+// text is gone from the new text, so it does not move the numbering on.
+export function diffLines(segments: TextSegment[]): DiffLine[] {
+	let number = 1
+	const lines: DiffLine[] = [{ number: number, segments: [], changed: false }]
+
+	for (const segment of segments) {
+		for (const [index, text] of segment.text.split("\n").entries()) {
+			if (index > 0) {
+				// a newline that was added or removed changes the line it ends
+				const ended = lines[lines.length - 1]
+				if (ended && segment.kind !== TextSegmentKind.Equal) {
+					ended.changed = true
+				}
+
+				if (segment.kind !== TextSegmentKind.Removed) {
+					number++
+				}
+
+				lines.push({ number: number, segments: [], changed: false })
+			}
+
+			const line = lines[lines.length - 1]
+			if (line && text) {
+				line.segments.push({ kind: segment.kind, text: text })
+				line.changed ||= segment.kind !== TextSegmentKind.Equal
+			}
+		}
+	}
+
+	for (const line of lines) {
+		const onlyRemoved =
+			line.segments.length > 0 &&
+			line.segments.every((s) => s.kind === TextSegmentKind.Removed)
+		if (onlyRemoved) {
+			line.number = null
+		}
+	}
+
+	return lines
+}
+
+// strip the indentation all lines share, so a snippet from deep inside the
+// code starts at the left edge. Only unchanged text counts as indentation,
+// so a changed indent still shows. An empty line has no say.
+export function dedentLines<T extends DiffLine>(lines: T[]): T[] {
+	const indents = lines
+		.filter((line) => line.segments.length > 0)
+		.map((line) => {
+			const first = line.segments[0]
+
+			return first?.kind === TextSegmentKind.Equal
+				? (INDENT_RE.exec(first.text)?.[0].length ?? 0)
+				: 0
+		})
+	const shared = indents.length > 0 ? Math.min(...indents) : 0
+	if (shared === 0) {
+		return lines
+	}
+
+	return lines.map((line) => {
+		const [first, ...rest] = line.segments
+		if (!first) {
+			return line
+		}
+
+		const text = first.text.slice(shared)
+
+		return {
+			...line,
+			segments: text ? [{ ...first, text: text }, ...rest] : rest,
+		}
+	})
+}
diff --git a/web/app/components/editor/blocks/metrics/MainBlock.vue b/web/app/components/editor/blocks/metrics/MainBlock.vue
index 62b9edd8..c0b36545 100644
--- a/web/app/components/editor/blocks/metrics/MainBlock.vue
+++ b/web/app/components/editor/blocks/metrics/MainBlock.vue
@@ -12,6 +12,7 @@ import {
 } from "./utils"
 import { DiffStatus } from "~/components/editor/diff/position-map"
 import DiffChangeMarker from "~/components/editor/diff/DiffChangeMarker.vue"
+import MetricDiffDetails from "./MetricDiffDetails.vue"
 
 // legacy blobs may miss fields entirely and may still use the old "type"
 // field name, so Partial reflects the actual runtime shape.
@@ -371,7 +372,9 @@ function disableVisualizationRefreshTemporarily() {
 				<div
 					class="absolute top-1 right-1.5 z-1 flex items-center rounded-md bg-background pl-0.5"
 				>
-					<DiffChangeMarker :node="props.node" class="mr-1" />
+					<DiffChangeMarker :node="props.node" class="mr-1">
+						<MetricDiffDetails :node="props.node" />
+					</DiffChangeMarker>
 					<ShadcnUiTooltip v-if="simulationVisible">
 						<ShadcnUiTooltipTrigger as-child>
 							<Icon
diff --git a/web/app/components/editor/blocks/metrics/MetricDiffDetails.nuxt.test.ts b/web/app/components/editor/blocks/metrics/MetricDiffDetails.nuxt.test.ts
new file mode 100644
index 00000000..3b4f8b94
--- /dev/null
+++ b/web/app/components/editor/blocks/metrics/MetricDiffDetails.nuxt.test.ts
@@ -0,0 +1,200 @@
+import { mountSuspended } from "@nuxt/test-utils/runtime"
+import { afterEach, beforeEach, describe, it } from "vitest"
+import MetricDiffDetails from "./MetricDiffDetails.vue"
+import { makeNode } from "../../test-helpers/node-view"
+import { METRIC_BLOCK_NAME } from "../node-names"
+import {
+	RefreshInterval,
+	TimeRangePreset,
+	VisualizationTimeUnit,
+} from "./utils"
+import { DiffStatus } from "~/components/editor/diff/position-map"
+import { settleMutations, t } from "~/components/test-helpers"
+import {
+	clearQueryCache,
+	disposeMockEndpoints,
+	mockEndpoint,
+} from "~/composables/api/test-helpers"
+
+// the data source list lives in the app-wide query cache
+describe("<MetricDiffDetails>", { concurrent: false }, () => {
+	beforeEach(() => {
+		clearQueryCache()
+	})
+
+	afterEach(() => {
+		disposeMockEndpoints()
+	})
+
+	it("labels each field of an added query by the query's number", async ({
+		expect,
+	}) => {
+		const wrapper = await mountDetails(
+			{ queries: [query("up", "")] },
+			{ queries: [query("up", ""), query("rate(x[5m])", "{{job}}")] },
+		)
+
+		expect(rows(wrapper)).toEqual([
+			[
+				t("editor.metrics.config.query-name-default-format", { index: 2 }),
+				null,
+				"rate(x[5m])",
+			],
+			[t("editor.metrics.diff.legend", { index: 2 }), null, "{{job}}"],
+		])
+		expect(wrapper.findAll("dd").every((dd) => dd.classes("font-mono"))).toBe(
+			true,
+		)
+	})
+
+	it("shows an empty legend as auto", async ({ expect }) => {
+		const wrapper = await mountDetails(
+			{ queries: [query("up", "{{job}}")] },
+			{ queries: [query("up", "")] },
+		)
+
+		expect(rows(wrapper)).toEqual([
+			[
+				t("editor.metrics.diff.legend", { index: 1 }),
+				"{{job}}",
+				t("editor.diff-change-marker.auto"),
+			],
+		])
+	})
+
+	it.for([
+		{ name: "decimal places", input: "decimals", label: "decimals-label" },
+		{ name: "min value", input: "axisBoundsMin", label: "bounds-min-label" },
+		{ name: "max value", input: "axisBoundsMax", label: "bounds-max-label" },
+	])(
+		"shows auto as the old $name when it was not set",
+		async ({ input, label }, { expect }) => {
+			const wrapper = await mountDetails({}, { [input]: 1 })
+
+			expect(rows(wrapper)).toEqual([
+				[
+					t(`editor.metrics.config.${label}`),
+					t("editor.diff-change-marker.auto"),
+					"1",
+				],
+			])
+		},
+	)
+
+	it("shows a setting that was not set before as empty", async ({ expect }) => {
+		const wrapper = await mountDetails(
+			{},
+			{ unitType: VisualizationTimeUnit.Seconds },
+		)
+
+		expect(rows(wrapper)).toEqual([
+			[
+				t("editor.metrics.config.unit-label"),
+				t("editor.diff-change-marker.empty"),
+				t("editor.metrics.config.unit-options.time.options.seconds"),
+			],
+		])
+	})
+
+	it("shows the settings by the names the config modal uses", async ({
+		expect,
+	}) => {
+		const wrapper = await mountDetails(
+			{
+				timeRange: TimeRangePreset.Last15Minutes,
+				refreshInterval: RefreshInterval.M1,
+				thresholds: [{ value: 1 }],
+			},
+			{
+				timeRange: TimeRangePreset.Last5Minutes,
+				refreshInterval: RefreshInterval.M5,
+				thresholds: [{ value: 1 }, { value: 2 }],
+			},
+		)
+
+		expect(rows(wrapper)).toEqual([
+			[
+				t("editor.metrics.config.time-range-label"),
+				t("editor.metrics.config.time-range-options.last_15_minutes"),
+				t("editor.metrics.config.time-range-options.last_5_minutes"),
+			],
+			[
+				t("editor.metrics.config.refresh-interval-label"),
+				t("editor.metrics.config.refresh-interval-options.1m"),
+				t("editor.metrics.config.refresh-interval-options.5m"),
+			],
+			[t("editor.metrics.config.thresholds-label"), "1", "2"],
+		])
+	})
+
+	it("names a data source instead of showing its id", async ({ expect }) => {
+		mockEndpoint("GET", "/api/data-sources", () => [
+			{ id: "ds-1", name: "Demo", type: "prometheus", url: "demo://x" },
+		])
+
+		const wrapper = await mountDetails(
+			{ dataSourceId: "ds-gone" },
+			{ dataSourceId: "ds-1" },
+		)
+		await settleMutations()
+
+		expect(rows(wrapper)).toEqual([
+			[
+				t("editor.metrics.config.data-source-label"),
+				t("editor.metrics.config.data-source-label-deleted"),
+				"Demo",
+			],
+		])
+	})
+
+	it("shows an attribute it has no label for by its name", async ({
+		expect,
+	}) => {
+		const wrapper = await mountDetails(
+			{ config: { title: "CPU" } },
+			{ config: { title: "RAM" } },
+		)
+
+		expect(rows(wrapper)).toEqual([
+			["config", '{"title":"CPU"}', '{"title":"RAM"}'],
+		])
+	})
+})
+
+function query(expr: string, legendFormat: string) {
+	return { name: "Query", query: expr, legendFormat: legendFormat }
+}
+
+// each row as its label, its old value and its new value, null for a side
+// the row does not show
+function rows(wrapper: Awaited<ReturnType<typeof mountDetails>>) {
+	const labels = wrapper.findAll("dt")
+
+	return wrapper
+		.findAll("dd")
+		.map((dd, index) => [
+			labels[index]?.text(),
+			dd.find(".line-through").exists() ? dd.get(".line-through").text() : null,
+			dd.find(".bg-diff-text-added").exists()
+				? dd.get(".bg-diff-text-added").text()
+				: null,
+		])
+}
+
+function mountDetails(
+	oldAttrs: Record<string, unknown>,
+	newAttrs: Record<string, unknown>,
+) {
+	return mountSuspended(MetricDiffDetails, {
+		props: {
+			node: makeNode(
+				{
+					...newAttrs,
+					diffStatus: DiffStatus.Modified,
+					oldNode: { attrs: oldAttrs },
+				},
+				{ typeName: METRIC_BLOCK_NAME },
+			),
+		},
+	})
+}
diff --git a/web/app/components/editor/blocks/metrics/MetricDiffDetails.vue b/web/app/components/editor/blocks/metrics/MetricDiffDetails.vue
new file mode 100644
index 00000000..a405e0a0
--- /dev/null
+++ b/web/app/components/editor/blocks/metrics/MetricDiffDetails.vue
@@ -0,0 +1,161 @@
+<script lang="ts" setup>
+import type { Node as PMNode } from "@tiptap/pm/model"
+import {
+	collectAttributeChanges,
+	displayValue,
+	formatChange,
+	type AttributeChange,
+	type FieldChange,
+} from "~/components/editor/diff/change-count"
+import DiffFieldChanges from "~/components/editor/diff/DiffFieldChanges.vue"
+import {
+	VisualizationDataUnit,
+	VisualizationMiscUnit,
+	VisualizationTimeUnit,
+} from "./utils"
+
+// matches the per-field units of queries, such as "queries.1.legendFormat"
+const QUERY_FIELD_RE = /^queries\.(\d+)\.(query|legendFormat)$/
+
+const UNIT_CATEGORIES: Record<string, string> = Object.fromEntries([
+	...Object.values(VisualizationTimeUnit).map(unitCategory("time")),
+	...Object.values(VisualizationDataUnit).map(unitCategory("data")),
+	...Object.values(VisualizationMiscUnit).map(unitCategory("misc")),
+])
+
+const props = defineProps<{
+	node: PMNode
+}>()
+
+const { t } = useI18n({ useScope: "global" })
+const { fetchDataSources } = useDataSourceAPI()
+
+const rows = computed<FieldChange[]>(() =>
+	collectAttributeChanges(props.node).map(toRow),
+)
+
+function toRow(change: AttributeChange): FieldChange {
+	const queryField = QUERY_FIELD_RE.exec(change.name)
+	if (queryField) {
+		const index = Number(queryField[1]) + 1
+		const label =
+			queryField[2] === "query"
+				? t("editor.metrics.config.query-name-default-format", { index })
+				: t("editor.metrics.diff.legend", { index })
+
+		// an empty legend falls back to the series labels, which the config
+		// modal calls auto
+		const format = (value: unknown) =>
+			value === "" && queryField[2] === "legendFormat"
+				? t("editor.diff-change-marker.auto")
+				: displayValue(value)
+
+		return { label: label, ...formatChange(change, format), code: true }
+	}
+
+	switch (change.name) {
+		case "title":
+			return row(t("editor.metrics.config.title-label"), change)
+		case "dataSourceId":
+			return row(
+				t("editor.metrics.config.data-source-label"),
+				change,
+				dataSourceName,
+			)
+		case "visualizationType":
+			return row(t("editor.metrics.diff.visualization"), change, (value) =>
+				t(
+					`editor.metrics.config.type-options.${displayValue(value).replace("_", "-")}.title`,
+				),
+			)
+		case "timeRange":
+			return row(t("editor.metrics.config.time-range-label"), change, (value) =>
+				t(`editor.metrics.config.time-range-options.${displayValue(value)}`),
+			)
+		case "refreshInterval":
+			return row(
+				t("editor.metrics.config.refresh-interval-label"),
+				change,
+				(value) =>
+					t(
+						`editor.metrics.config.refresh-interval-options.${displayValue(value)}`,
+					),
+			)
+		case "thresholds":
+			return row(t("editor.metrics.config.thresholds-label"), change, (value) =>
+				String((value as unknown[]).length),
+			)
+		case "baseThresholdColor":
+			return row(t("editor.metrics.diff.base-threshold-color"), change)
+		case "decimals":
+			return autoRow(t("editor.metrics.config.decimals-label"), change)
+		case "unitType":
+			return row(t("editor.metrics.config.unit-label"), change, unitName)
+		case "unitCustom":
+			return row(t("editor.metrics.diff.custom-unit"), change)
+		case "axisBoundsMin":
+			return autoRow(t("editor.metrics.config.bounds-min-label"), change)
+		case "axisBoundsMax":
+			return autoRow(t("editor.metrics.config.bounds-max-label"), change)
+		case "simulationPreset":
+			return row(t("editor.metrics.simulation.preset-label"), change, (value) =>
+				t(`editor.metrics.simulation.preset-options.${displayValue(value)}`),
+			)
+		case "width":
+			return row(t("editor.metrics.diff.size"), change, (value) =>
+				t(
+					`editor.drag-handle.options.metric-block.width-options.${displayValue(value)}`,
+				),
+			)
+		default:
+			// an attribute this card has no label for still shows, so the
+			// card lists every change the marker counts
+			return row(change.name, change)
+	}
+}
+
+// a setting always has a value, so its unset side shows as empty
+function row(
+	label: string,
+	change: AttributeChange,
+	format?: (value: unknown) => string,
+): FieldChange {
+	return { label: label, ...formatChange(change, format, "") }
+}
+
+// a setting whose unset value lets the chart pick one, as its placeholder
+// in the config modal says
+function autoRow(label: string, change: AttributeChange): FieldChange {
+	return {
+		label: label,
+		...formatChange(change, displayValue, t("editor.diff-change-marker.auto")),
+	}
+}
+
+function unitCategory(category: string) {
+	return (unit: string): [string, string] => [unit, category]
+}
+
+function dataSourceName(id: unknown): string {
+	const dataSource = fetchDataSources.state.value.data?.find(
+		(source) => source.id === id,
+	)
+
+	return (
+		dataSource?.name ?? t("editor.metrics.config.data-source-label-deleted")
+	)
+}
+
+function unitName(value: unknown): string {
+	const unit = displayValue(value)
+	const category = UNIT_CATEGORIES[unit]
+
+	return category
+		? t(`editor.metrics.config.unit-options.${category}.options.${unit}`)
+		: t(`editor.metrics.config.unit-options.${unit}`)
+}
+</script>
+
+<template>
+	<DiffFieldChanges class="w-80" :rows="rows" />
+</template>
diff --git a/web/app/components/editor/diff/DiffBeforeAfter.nuxt.test.ts b/web/app/components/editor/diff/DiffBeforeAfter.nuxt.test.ts
new file mode 100644
index 00000000..4661c1e0
--- /dev/null
+++ b/web/app/components/editor/diff/DiffBeforeAfter.nuxt.test.ts
@@ -0,0 +1,52 @@
+import { mountSuspended } from "@nuxt/test-utils/runtime"
+import { describe, it } from "vitest"
+import { h } from "vue"
+import DiffBeforeAfter from "./DiffBeforeAfter.vue"
+
+describe("<DiffBeforeAfter>", () => {
+	it("renders each set side through the slot", async ({ expect }) => {
+		const wrapper = await mountSides("a.png", "b.png")
+
+		expect(wrapper.findAll(".side").map((side) => side.text())).toEqual([
+			"a.png",
+			"b.png",
+		])
+		expect(wrapper.text()).not.toContain("nothing")
+	})
+
+	it.for([
+		{
+			name: "shows the empty label for a side that was not set before",
+			input: [undefined, "b.png"],
+			expected: ["nothing", "b.png"],
+		},
+		{
+			name: "shows the empty label for a side that is not set after",
+			input: ["a.png", undefined],
+			expected: ["a.png", "nothing"],
+		},
+	])("$name", async ({ input, expected }, { expect }) => {
+		const wrapper = await mountSides(input[0], input[1])
+		const boxes = wrapper.findAll(".border-2").map((box) => box.text())
+
+		expect(boxes).toEqual(expected)
+	})
+
+	it("borders the old side red and the new side green", async ({ expect }) => {
+		const wrapper = await mountSides("a.png", "b.png")
+		const boxes = wrapper.findAll(".border-2")
+
+		expect(boxes[0]?.classes()).toContain("border-diff-removed")
+		expect(boxes[1]?.classes()).toContain("border-diff-added")
+	})
+})
+
+function mountSides(before: string | undefined, after: string | undefined) {
+	return mountSuspended(DiffBeforeAfter, {
+		props: { before: before, after: after, emptyLabel: "nothing" },
+		slots: {
+			default: ({ value }: { value: unknown }) =>
+				h("span", { class: "side" }, String(value)),
+		},
+	})
+}
diff --git a/web/app/components/editor/diff/DiffBeforeAfter.vue b/web/app/components/editor/diff/DiffBeforeAfter.vue
new file mode 100644
index 00000000..32ab69cf
--- /dev/null
+++ b/web/app/components/editor/diff/DiffBeforeAfter.vue
@@ -0,0 +1,48 @@
+<script lang="ts" setup generic="T">
+import { cn } from "~/lib/utils"
+
+// an undefined side had nothing set, so it shows emptyLabel instead. Both
+// sides take the same width, and the taller one sets the height of both.
+const props = defineProps<{
+	before?: T
+	after?: T
+	emptyLabel: string
+}>()
+
+defineSlots<{
+	default: (props: { value: T }) => unknown
+}>()
+
+const sides = computed(() => [
+	{ key: "before", value: props.before, borderClass: "border-diff-removed" },
+	{ key: "after", value: props.after, borderClass: "border-diff-added" },
+])
+</script>
+
+<template>
+	<div class="grid grid-cols-[minmax(0,1fr)_auto_minmax(0,1fr)] gap-2">
+		<template v-for="(side, index) in sides" :key="side.key">
+			<Icon
+				v-if="index > 0"
+				name="mingcute:arrow-right-line"
+				class="size-3.5 self-center text-muted-foreground"
+			/>
+			<div
+				:class="
+					cn(
+						'flex min-h-14 items-center justify-center overflow-hidden rounded-md border-2',
+						side.borderClass,
+					)
+				"
+			>
+				<slot v-if="side.value !== undefined" :value="side.value" />
+				<span
+					v-else
+					class="px-2 text-center text-xs text-muted-foreground italic"
+				>
+					{{ props.emptyLabel }}
+				</span>
+			</div>
+		</template>
+	</div>
+</template>
diff --git a/web/app/components/editor/diff/DiffChangeMarker.nuxt.test.ts b/web/app/components/editor/diff/DiffChangeMarker.nuxt.test.ts
index cbf4111e..4257588d 100644
--- a/web/app/components/editor/diff/DiffChangeMarker.nuxt.test.ts
+++ b/web/app/components/editor/diff/DiffChangeMarker.nuxt.test.ts
@@ -1,9 +1,17 @@
 import { mountSuspended } from "@nuxt/test-utils/runtime"
-import { describe, it } from "vitest"
+import { beforeEach, describe, it, vi } from "vitest"
+import { flushPromises } from "@vue/test-utils"
+import { defineComponent, h } from "vue"
 import DiffChangeMarker from "./DiffChangeMarker.vue"
 import { DiffStatus } from "./position-map"
 import { makeNode } from "../test-helpers/node-view"
-import { t } from "~/components/test-helpers"
+import { clearTeleportedOverlays, t } from "~/components/test-helpers"
+
+const MODIFIED_IMAGE = {
+	src: "b.png",
+	diffStatus: DiffStatus.Modified,
+	oldNode: { attrs: { src: "a.png" } },
+}
 
 describe("DiffChangeMarker", () => {
 	it("shows the removals and additions of a modified node", async ({
@@ -63,10 +71,88 @@ describe("DiffChangeMarker", () => {
 			expect(wrapper.html()).toBe("<!--v-if-->")
 		},
 	)
+
+	// the card lands in <body>, which every test in the file shares
+	describe("when clicked", { concurrent: false }, () => {
+		beforeEach(() => {
+			clearTeleportedOverlays()
+		})
+
+		it("opens the details from its slot", async ({ expect }) => {
+			const wrapper = await mountMarker(MODIFIED_IMAGE, () => "image details")
+
+			await wrapper.get("span").trigger("click")
+
+			expect(document.body.textContent).toContain("image details")
+		})
+
+		it("closes the details on a click elsewhere", async ({ expect }) => {
+			const wrapper = await mountMarker(MODIFIED_IMAGE, () => "image details")
+			await wrapper.get("span").trigger("click")
+			// the popover's outside-click listener is attached a task after it
+			// opens
+			await new Promise((resolve) => setTimeout(resolve, 0))
+
+			document.body.dispatchEvent(
+				new PointerEvent("pointerdown", { bubbles: true, button: 0 }),
+			)
+			await flushPromises()
+
+			expect(document.body.textContent).not.toContain("image details")
+		})
+
+		it("looks clickable only when it has details", async ({ expect }) => {
+			const withDetails = await mountMarker(MODIFIED_IMAGE, () => "details")
+			const withoutDetails = await mountMarker(MODIFIED_IMAGE)
+
+			expect(withDetails.get("span").classes()).toEqual(
+				expect.arrayContaining(["cursor-pointer", "active:opacity-90"]),
+			)
+			expect(withoutDetails.get("span").classes()).not.toContain(
+				"cursor-pointer",
+			)
+			expect(withoutDetails.get("span").classes()).not.toContain(
+				"active:opacity-90",
+			)
+		})
+
+		it("opens no card when it has no details", async ({ expect }) => {
+			const wrapper = await mountMarker(MODIFIED_IMAGE)
+
+			await wrapper.get("span").trigger("click")
+
+			expect(
+				document.body.querySelector("[data-slot='popover-content']"),
+			).toBeNull()
+		})
+	})
+
+	describe("inside a link", () => {
+		it("keeps a click on the pill from reaching the element around it", async ({
+			expect,
+		}) => {
+			const onClick = vi.fn()
+			const wrapper = await mountSuspended(
+				defineComponent({
+					render: () =>
+						h("a", { href: "#file", onClick: onClick }, [
+							h(DiffChangeMarker, { node: makeNode(MODIFIED_IMAGE) }),
+						]),
+				}),
+			)
+
+			const event = new MouseEvent("click", { bubbles: true, cancelable: true })
+			wrapper.get("a > span").element.dispatchEvent(event)
+
+			expect(event.defaultPrevented).toBe(true)
+			expect(onClick).not.toHaveBeenCalled()
+		})
+	})
 })
 
-function mountMarker(attrs: Record<string, unknown>) {
+function mountMarker(attrs: Record<string, unknown>, details?: () => string) {
 	return mountSuspended(DiffChangeMarker, {
 		props: { node: makeNode(attrs) },
+		slots: details ? { default: details } : {},
 	})
 }
diff --git a/web/app/components/editor/diff/DiffChangeMarker.vue b/web/app/components/editor/diff/DiffChangeMarker.vue
index f397af71..2ccf75bd 100644
--- a/web/app/components/editor/diff/DiffChangeMarker.vue
+++ b/web/app/components/editor/diff/DiffChangeMarker.vue
@@ -1,8 +1,16 @@
 <script lang="ts" setup>
 import type { Node as PMNode } from "@tiptap/pm/model"
+import { cn } from "~/lib/utils"
 import { countNodeChanges } from "./change-count"
 import { DiffStatus } from "./position-map"
 
+// the classes that place the marker belong on the pill, not on the popover
+// root, which renders no element of its own. The pill sits inside the file
+// card's link and the empty blocks' buttons, so a click on it stops there.
+defineOptions({
+	inheritAttrs: false,
+})
+
 const props = defineProps<{
 	node: PMNode
 }>()
@@ -15,27 +23,48 @@ const count = computed(() =>
 </script>
 
 <template>
-	<span
-		v-if="count && (count.removed || count.added)"
-		contenteditable="false"
-		class="pointer-events-none flex overflow-hidden rounded-full border border-border bg-background text-xs font-semibold select-none"
-	>
-		<span class="sr-only">
-			{{ $t("editor.diff-change-marker.label", { ...count }) }}
-		</span>
-		<span
-			v-if="count.removed"
-			aria-hidden="true"
-			class="bg-diff-removed px-2 py-0.5 text-diff-removed-foreground"
+	<ShadcnUiPopover v-if="count && (count.removed || count.added)">
+		<ShadcnUiPopoverTrigger as-child :disabled="!$slots.default">
+			<span
+				v-bind="$attrs"
+				contenteditable="false"
+				:class="
+					cn(
+						'flex overflow-hidden rounded-full border border-border bg-background text-xs font-semibold transition-all select-none',
+						$slots.default &&
+							'cursor-pointer active:opacity-90 [&:hover:not(:active)]:opacity-70',
+					)
+				"
+				@click.stop.prevent
+			>
+				<span class="sr-only">
+					{{ $t("editor.diff-change-marker.label", { ...count }) }}
+				</span>
+				<span
+					v-if="count.removed"
+					aria-hidden="true"
+					class="bg-diff-removed px-2 py-0.5 text-diff-removed-foreground"
+				>
+					{{
+						$t("editor.diff-change-marker.removed", { count: count.removed })
+					}}
+				</span>
+				<span
+					v-if="count.added"
+					aria-hidden="true"
+					class="bg-diff-added px-2 py-0.5 text-diff-added-foreground"
+				>
+					{{ $t("editor.diff-change-marker.added", { count: count.added }) }}
+				</span>
+			</span>
+		</ShadcnUiPopoverTrigger>
+		<ShadcnUiPopoverContent
+			v-if="$slots.default"
+			align="end"
+			class="w-auto max-w-[min(28rem,90dvw)] p-3"
 		>
-			{{ $t("editor.diff-change-marker.removed", { count: count.removed }) }}
-		</span>
-		<span
-			v-if="count.added"
-			aria-hidden="true"
-			class="bg-diff-added px-2 py-0.5 text-diff-added-foreground"
-		>
-			{{ $t("editor.diff-change-marker.added", { count: count.added }) }}
-		</span>
-	</span>
+			<!-- the details of the changes, from the block around the marker -->
+			<slot />
+		</ShadcnUiPopoverContent>
+	</ShadcnUiPopover>
 </template>
diff --git a/web/app/components/editor/diff/DiffFieldChanges.nuxt.test.ts b/web/app/components/editor/diff/DiffFieldChanges.nuxt.test.ts
new file mode 100644
index 00000000..0f146359
--- /dev/null
+++ b/web/app/components/editor/diff/DiffFieldChanges.nuxt.test.ts
@@ -0,0 +1,65 @@
+import { mountSuspended } from "@nuxt/test-utils/runtime"
+import { describe, it } from "vitest"
+import DiffFieldChanges from "./DiffFieldChanges.vue"
+import type { FieldChange } from "./change-count"
+import { t } from "~/components/test-helpers"
+
+describe("<DiffFieldChanges>", () => {
+	it("shows a changed field's label, old value and new value", async ({
+		expect,
+	}) => {
+		const wrapper = await mountFields([
+			{ label: "Title", oldValue: "CPU", newValue: "CPU usage" },
+		])
+
+		expect(wrapper.get("dt").text()).toBe("Title")
+		expect(wrapper.get(".line-through").text()).toBe("CPU")
+		expect(wrapper.get(".bg-diff-text-added").text()).toBe("CPU usage")
+		expect(wrapper.find(".iconify").exists()).toBe(true)
+	})
+
+	it("shows only the new value of a newly set field", async ({ expect }) => {
+		const wrapper = await mountFields([
+			{ label: "Unit", oldValue: null, newValue: "percent" },
+		])
+
+		expect(wrapper.find(".line-through").exists()).toBe(false)
+		expect(wrapper.get(".bg-diff-text-added").text()).toBe("percent")
+		expect(wrapper.find(".iconify").exists()).toBe(false)
+	})
+
+	it("shows only the old value of a cleared field", async ({ expect }) => {
+		const wrapper = await mountFields([
+			{ label: "Unit", oldValue: "percent", newValue: null },
+		])
+
+		expect(wrapper.get(".line-through").text()).toBe("percent")
+		expect(wrapper.find(".bg-diff-text-added").exists()).toBe(false)
+	})
+
+	it("names an empty value instead of leaving it blank", async ({ expect }) => {
+		const wrapper = await mountFields([
+			{ label: "Legend 2", oldValue: null, newValue: "" },
+		])
+
+		expect(wrapper.get(".bg-diff-text-added").text()).toBe(
+			t("editor.diff-change-marker.empty"),
+		)
+	})
+
+	it("sets code values in a monospace font", async ({ expect }) => {
+		const wrapper = await mountFields([
+			{ label: "Query 2", oldValue: null, newValue: "up", code: true },
+			{ label: "Title", oldValue: null, newValue: "CPU" },
+		])
+
+		expect(wrapper.findAll("dd").map((dd) => dd.classes("font-mono"))).toEqual([
+			true,
+			false,
+		])
+	})
+})
+
+function mountFields(rows: FieldChange[]) {
+	return mountSuspended(DiffFieldChanges, { props: { rows: rows } })
+}
diff --git a/web/app/components/editor/diff/DiffFieldChanges.vue b/web/app/components/editor/diff/DiffFieldChanges.vue
new file mode 100644
index 00000000..21183343
--- /dev/null
+++ b/web/app/components/editor/diff/DiffFieldChanges.vue
@@ -0,0 +1,44 @@
+<script lang="ts" setup>
+import { cn } from "~/lib/utils"
+import type { FieldChange } from "./change-count"
+
+const props = defineProps<{
+	rows: FieldChange[]
+}>()
+</script>
+
+<template>
+	<dl
+		class="grid grid-cols-[auto_minmax(0,1fr)] items-baseline gap-x-4 gap-y-1.5 text-xs"
+	>
+		<template v-for="(row, index) in props.rows" :key="index">
+			<dt class="whitespace-nowrap text-muted-foreground">{{ row.label }}</dt>
+			<dd
+				:class="
+					cn(
+						'flex min-w-0 flex-wrap items-baseline gap-1',
+						row.code && 'font-mono',
+					)
+				"
+			>
+				<span
+					v-if="row.oldValue !== null"
+					class="rounded-sm bg-diff-text-removed px-1 break-all line-through"
+				>
+					{{ row.oldValue || $t("editor.diff-change-marker.empty") }}
+				</span>
+				<Icon
+					v-if="row.oldValue !== null && row.newValue !== null"
+					name="mingcute:arrow-right-line"
+					class="size-3 shrink-0 self-center text-muted-foreground"
+				/>
+				<span
+					v-if="row.newValue !== null"
+					class="rounded-sm bg-diff-text-added px-1 break-all"
+				>
+					{{ row.newValue || $t("editor.diff-change-marker.empty") }}
+				</span>
+			</dd>
+		</template>
+	</dl>
+</template>
diff --git a/web/app/components/editor/diff/change-count.test.ts b/web/app/components/editor/diff/change-count.test.ts
index bd9d02c3..36b10ba7 100644
--- a/web/app/components/editor/diff/change-count.test.ts
+++ b/web/app/components/editor/diff/change-count.test.ts
@@ -1,6 +1,13 @@
 import { Schema, type Node as PMNode } from "@tiptap/pm/model"
 import { describe, it } from "vitest"
-import { countNodeChanges } from "./change-count"
+import {
+	collectAttributeChanges,
+	countNodeChanges,
+	displayValue,
+	formatChange,
+	TextSegmentKind,
+	textSegments,
+} from "./change-count"
 import { DiffStatus } from "./position-map"
 import {
 	COMMENT_MARK_NAME,
@@ -11,6 +18,7 @@ import { NODE_COMMENT_ID_ATTR } from "~/components/editor/attribute-names"
 import { SIMULATION_ACTIVE_ATTR } from "~/components/editor/blocks/metrics/simulation"
 import {
 	FILE_BLOCK_NAME,
+	IMAGE_BLOCK_NAME,
 	METRIC_BLOCK_NAME,
 } from "~/components/editor/blocks/node-names"
 
@@ -39,6 +47,19 @@ const schema = new Schema({
 				oldNode: { default: null },
 			},
 		},
+		[IMAGE_BLOCK_NAME]: {
+			group: "block",
+			atom: true,
+			attrs: {
+				uid: { default: null },
+				src: { default: null },
+				alt: { default: null },
+				title: { default: null },
+				width: { default: null },
+				diffStatus: { default: null },
+				oldNode: { default: null },
+			},
+		},
 		[FILE_BLOCK_NAME]: {
 			group: "block",
 			atom: true,
@@ -143,6 +164,24 @@ describe("countNodeChanges", () => {
 		expect(countNodeChanges(node)).toEqual(expected)
 	})
 
+	it("ignores the image attributes no one can change from the editor", ({
+		expect,
+	}) => {
+		const node = schema.nodes[IMAGE_BLOCK_NAME].create({
+			uid: "image-1",
+			src: "a.png",
+			alt: "a dog",
+			title: "Dog",
+			diffStatus: DiffStatus.Modified,
+			oldNode: {
+				type: IMAGE_BLOCK_NAME,
+				attrs: { uid: "image-1", src: "a.png", alt: "a cat" },
+			},
+		})
+
+		expect(countNodeChanges(node)).toEqual({ removed: 0, added: 0 })
+	})
+
 	it("counts no attribute changes on a node without its original", ({
 		expect,
 	}) => {
@@ -172,12 +211,12 @@ describe("countNodeChanges", () => {
 			expected: { removed: 1, added: 0 },
 		},
 		{
-			name: "counts the attributes outside the file group on their own",
+			name: "ignores the flag of an upload in flight",
 			input: {
 				old: storedFile("a.zip"),
 				new: { ...storedFile("a.zip"), uploading: true },
 			},
-			expected: { removed: 1, added: 1 },
+			expected: { removed: 0, added: 0 },
 		},
 	])("$name", ({ input, expected }, { expect }) => {
 		const node = schema.nodes[FILE_BLOCK_NAME].create({
@@ -294,6 +333,134 @@ describe("countNodeChanges", () => {
 	})
 })
 
+describe("collectAttributeChanges", () => {
+	it("lists each changed unit with both of its sides", ({ expect }) => {
+		const node = schema.nodes.atom.create({
+			uid: "block-1",
+			src: "b.png",
+			alt: "a cat",
+			diffStatus: DiffStatus.Modified,
+			oldNode: {
+				type: "atom",
+				attrs: { uid: "block-1", src: "a.png", width: 300 },
+			},
+		})
+
+		expect(collectAttributeChanges(node)).toEqual([
+			{ name: "src", oldValue: "a.png", newValue: "b.png" },
+			{ name: "width", oldValue: 300, newValue: undefined },
+			{ name: "alt", oldValue: undefined, newValue: "a cat" },
+		])
+	})
+
+	it("gives a group's side as the record of its set attributes", ({
+		expect,
+	}) => {
+		const node = schema.nodes[FILE_BLOCK_NAME].create({
+			uid: "file-1",
+			...storedFile("b.zip"),
+			diffStatus: DiffStatus.Modified,
+			oldNode: {
+				type: FILE_BLOCK_NAME,
+				attrs: { uid: "file-1", uploading: false },
+			},
+		})
+
+		expect(collectAttributeChanges(node)).toEqual([
+			{ name: "file", oldValue: undefined, newValue: storedFile("b.zip") },
+		])
+	})
+
+	it("names a list item's field by its list, index and field", ({ expect }) => {
+		const node = schema.nodes[METRIC_BLOCK_NAME].create({
+			uid: "metric-1",
+			queries: [query("up", ""), query("rate", "")],
+			diffStatus: DiffStatus.Modified,
+			oldNode: {
+				type: METRIC_BLOCK_NAME,
+				attrs: { uid: "metric-1", queries: [query("up", "")] },
+			},
+		})
+
+		expect(collectAttributeChanges(node)).toEqual([
+			{ name: "queries.1.query", oldValue: undefined, newValue: "rate" },
+			{ name: "queries.1.legendFormat", oldValue: undefined, newValue: "" },
+		])
+	})
+
+	it("lists nothing for a node without its original", ({ expect }) => {
+		const node = schema.nodes.atom.create({
+			src: "a.png",
+			diffStatus: DiffStatus.Modified,
+		})
+
+		expect(collectAttributeChanges(node)).toEqual([])
+	})
+})
+
+describe("displayValue", () => {
+	it.for([
+		{ name: "keeps a string as it is", input: "a cat", expected: "a cat" },
+		{ name: "prints a number", input: 480, expected: "480" },
+		{ name: "prints a boolean", input: true, expected: "true" },
+		{
+			name: "prints an object as stable JSON",
+			input: { b: 1, a: 2 },
+			expected: '{"a":2,"b":1}',
+		},
+	])("$name", ({ input, expected }, { expect }) => {
+		expect(displayValue(input)).toBe(expected)
+	})
+})
+
+describe("formatChange", () => {
+	it("formats both sides with the given format", ({ expect }) => {
+		expect(
+			formatChange(
+				{ name: "width", oldValue: 300, newValue: 480 },
+				(value) => `${displayValue(value)}!`,
+			),
+		).toEqual({ oldValue: "300!", newValue: "480!" })
+	})
+
+	it("shows the unset text for a side that is not set", ({ expect }) => {
+		expect(
+			formatChange(
+				{ name: "width", oldValue: undefined, newValue: 480 },
+				displayValue,
+				"auto",
+			),
+		).toEqual({ oldValue: "auto", newValue: "480" })
+	})
+
+	it("gives null for a side that is not set", ({ expect }) => {
+		expect(
+			formatChange({ name: "alt", oldValue: undefined, newValue: "a cat" }),
+		).toEqual({ oldValue: null, newValue: "a cat" })
+	})
+})
+
+describe("textSegments", () => {
+	it("joins neighbouring text of the same kind into one segment", ({
+		expect,
+	}) => {
+		const node = schema.nodes.code.create({ uid: "code-1" }, [
+			textNode("A-->", []),
+			textNode("B", [REMOVED]),
+			textNode("C", [ADDED]),
+			textNode("D", [ADDED, COMMENT_MARK_NAME]),
+			textNode(" end", []),
+		])
+
+		expect(textSegments(node)).toEqual([
+			{ kind: TextSegmentKind.Equal, text: "A-->" },
+			{ kind: TextSegmentKind.Removed, text: "B" },
+			{ kind: TextSegmentKind.Added, text: "CD" },
+			{ kind: TextSegmentKind.Equal, text: " end" },
+		])
+	})
+})
+
 function query(expr: string, legendFormat: string): Record<string, unknown> {
 	return { name: "Query", query: expr, legendFormat: legendFormat }
 }
diff --git a/web/app/components/editor/diff/change-count.ts b/web/app/components/editor/diff/change-count.ts
index 3fffd244..6b4e477c 100644
--- a/web/app/components/editor/diff/change-count.ts
+++ b/web/app/components/editor/diff/change-count.ts
@@ -4,10 +4,14 @@ import {
 	DIFF_TEXT_ADDED_MARK_NAME,
 	DIFF_TEXT_REMOVED_MARK_NAME,
 } from "~/components/editor/mark-names"
-import { NODE_COMMENT_ID_ATTR } from "~/components/editor/attribute-names"
+import {
+	NODE_COMMENT_ID_ATTR,
+	UPLOADING_ATTR,
+} from "~/components/editor/attribute-names"
 import { SIMULATION_ACTIVE_ATTR } from "~/components/editor/blocks/metrics/simulation"
 import {
 	FILE_BLOCK_NAME,
+	IMAGE_BLOCK_NAME,
 	METRIC_BLOCK_NAME,
 } from "~/components/editor/blocks/node-names"
 
@@ -29,8 +33,15 @@ const IGNORED_ATTRIBUTES = new Set([
 	...DIFF_META_ATTRIBUTES,
 	NODE_COMMENT_ID_ATTR,
 	SIMULATION_ACTIVE_ATTR,
+	UPLOADING_ATTR,
 ])
 
+// attributes no one can change from the editor, per node type. They only
+// arrive with pasted HTML, so they are not counted.
+const UNTRACKED_ATTRIBUTES: Record<string, string[]> = {
+	[IMAGE_BLOCK_NAME]: ["alt", "title"],
+}
+
 // attributes that change together and count as one change, per node
 // type. Each attribute maps to the name of its group.
 const ATTRIBUTE_GROUPS: Record<string, Record<string, string>> = {
@@ -50,47 +61,60 @@ const ITEM_FIELDS: Record<string, Record<string, string[]>> = {
 	},
 }
 
+export interface AttributeChange {
+	// the attribute's name, its group's name, or "<list>.<index>.<field>"
+	// for a field of a list item
+	name: string
+	// undefined on the side where the unit is not set. A group's value is
+	// the record of its set attributes.
+	oldValue: unknown
+	newValue: unknown
+}
+
+// one row of a card that lists changed fields
+export interface FieldChange {
+	label: string
+	// null on the side where the field is not set
+	oldValue: string | null
+	newValue: string | null
+	// code such as a query reads better in a monospace font
+	code?: boolean
+}
+
+export enum TextSegmentKind {
+	Equal = "equal",
+	Removed = "removed",
+	Added = "added",
+}
+
+export interface TextSegment {
+	kind: TextSegmentKind
+	text: string
+}
+
 // count the changes of a modified node against its original. A changed
 // attribute counts as one removal and one addition, a newly set one as an
 // addition and a cleared one as a removal. A group of attributes counts
 // like one attribute. Changed text counts by run.
 export function countNodeChanges(node: PMNode): ChangeCount {
-	// an expanded textblock drops its oldNode, since its marks carry the
-	// original instead
-	const oldNode = node.attrs.oldNode as JSONContent | null
-	const attributes = oldNode
-		? countAttributeChanges(node.type.name, oldNode.attrs ?? {}, node.attrs)
-		: { removed: 0, added: 0 }
-	const text = countTextChanges(node)
-
-	return {
-		removed: attributes.removed + text.removed,
-		added: attributes.added + text.added,
-	}
-}
-
-function countAttributeChanges(
-	typeName: string,
-	oldAttrs: Record<string, unknown>,
-	newAttrs: Record<string, unknown>,
-): ChangeCount {
 	const count: ChangeCount = { removed: 0, added: 0 }
-	const oldUnits = attributeUnits(typeName, oldAttrs)
-	const newUnits = attributeUnits(typeName, newAttrs)
-	const names = new Set([...oldUnits.keys(), ...newUnits.keys()])
 
-	for (const name of names) {
-		const oldUnit = oldUnits.get(name)
-		const newUnit = newUnits.get(name)
-		if (jsonStableStringify(oldUnit) === jsonStableStringify(newUnit)) {
-			continue
-		}
-
-		if (oldUnit) {
+	for (const change of collectAttributeChanges(node)) {
+		if (change.oldValue !== undefined) {
 			count.removed++
 		}
 
-		if (newUnit) {
+		if (change.newValue !== undefined) {
+			count.added++
+		}
+	}
+
+	for (const segment of textSegments(node)) {
+		if (segment.kind === TextSegmentKind.Removed) {
+			count.removed++
+		}
+
+		if (segment.kind === TextSegmentKind.Added) {
 			count.added++
 		}
 	}
@@ -98,6 +122,88 @@ function countAttributeChanges(
 	return count
 }
 
+export function collectAttributeChanges(node: PMNode): AttributeChange[] {
+	// an expanded textblock drops its oldNode, since its marks carry the
+	// original instead
+	const oldNode = node.attrs.oldNode as JSONContent | null
+	if (!oldNode) {
+		return []
+	}
+
+	const oldUnits = attributeUnits(node.type.name, oldNode.attrs ?? {})
+	const newUnits = attributeUnits(node.type.name, node.attrs)
+	const names = new Set([...oldUnits.keys(), ...newUnits.keys()])
+	const changes: AttributeChange[] = []
+
+	for (const name of names) {
+		const oldValue = oldUnits.get(name)
+		const newValue = newUnits.get(name)
+		if (jsonStableStringify(oldValue) !== jsonStableStringify(newValue)) {
+			changes.push({ name: name, oldValue: oldValue, newValue: newValue })
+		}
+	}
+
+	return changes
+}
+
+// the text a card shows for an attribute value
+export function displayValue(value: unknown): string {
+	if (typeof value === "string") {
+		return value
+	}
+
+	if (typeof value === "number" || typeof value === "boolean") {
+		return String(value)
+	}
+
+	return jsonStableStringify(value)
+}
+
+// both sides of a change as text. A side that is not set shows unset, or
+// is left out when unset is null.
+export function formatChange(
+	change: AttributeChange,
+	format: (value: unknown) => string = displayValue,
+	unset: string | null = null,
+): { oldValue: string | null; newValue: string | null } {
+	return {
+		oldValue: change.oldValue === undefined ? unset : format(change.oldValue),
+		newValue: change.newValue === undefined ? unset : format(change.newValue),
+	}
+}
+
+// a modified textblock holds both sides of its text, told apart by the
+// added and removed marks. Each unbroken run of one kind becomes one
+// segment, so several changes can sit on the same line.
+export function textSegments(node: PMNode): TextSegment[] {
+	const segments: TextSegment[] = []
+
+	node.descendants((child) => {
+		if (!child.isText) {
+			return true
+		}
+
+		const marks = child.marks.map((mark) => mark.type.name)
+		let kind = TextSegmentKind.Equal
+		if (marks.includes(DIFF_TEXT_REMOVED_MARK_NAME)) {
+			kind = TextSegmentKind.Removed
+		} else if (marks.includes(DIFF_TEXT_ADDED_MARK_NAME)) {
+			kind = TextSegmentKind.Added
+		}
+
+		const last = segments.at(-1)
+		if (last?.kind === kind) {
+			last.text += child.text ?? ""
+		} else {
+			segments.push({ kind: kind, text: child.text ?? "" })
+		}
+
+		return false
+	})
+
+	return segments
+}
+
 // sort the set attributes into units, keyed by their group name, or by
 // their own name when they have no group. A list attribute with item fields
 // becomes one unit per field of each item instead. A unit whose attributes
@@ -105,13 +211,19 @@ function countAttributeChanges(
 function attributeUnits(
 	typeName: string,
 	attrs: Record<string, unknown>,
-): Map<string, Record<string, unknown>> {
+): Map<string, unknown> {
 	const groups = ATTRIBUTE_GROUPS[typeName] ?? {}
 	const itemFields = ITEM_FIELDS[typeName] ?? {}
-	const units = new Map<string, Record<string, unknown>>()
+	const untracked = UNTRACKED_ATTRIBUTES[typeName] ?? []
+	const units = new Map<string, unknown>()
 
 	for (const [key, value] of Object.entries(attrs)) {
-		if (IGNORED_ATTRIBUTES.has(key) || value === null || value === undefined) {
+		if (
+			IGNORED_ATTRIBUTES.has(key) ||
+			untracked.includes(key) ||
+			value === null ||
+			value === undefined
+		) {
 			continue
 		}
 
@@ -121,15 +233,19 @@ function attributeUnits(
 			continue
 		}
 
-		const name = groups[key] ?? key
-		units.set(name, { ...units.get(name), [key]: value })
+		const group = groups[key]
+		if (group) {
+			units.set(group, { ...(units.get(group) as object), [key]: value })
+		} else {
+			units.set(key, value)
+		}
 	}
 
 	return units
 }
 
 function addItemUnits(
-	units: Map<string, Record<string, unknown>>,
+	units: Map<string, unknown>,
 	key: string,
 	items: Record<string, unknown>[],
 	fields: string[],
@@ -138,44 +254,8 @@ function addItemUnits(
 		for (const field of fields) {
 			const value = item[field]
 			if (value !== null && value !== undefined) {
-				units.set(`${key}.${index}.${field}`, { [field]: value })
+				units.set(`${key}.${index}.${field}`, value)
 			}
 		}
 	}
 }
-
-// a modified textblock holds both sides of its text, told apart by the
-// added and removed marks. Each unbroken run of one mark is one change,
-// so several can sit on the same line.
-function countTextChanges(node: PMNode): ChangeCount {
-	const count: ChangeCount = { removed: 0, added: 0 }
-	let previous: string | null = null
-
-	node.descendants((child) => {
-		if (!child.isText) {
-			return true
-		}
-
-		const marks = child.marks.map((mark) => mark.type.name)
-		let current: string | null = null
-		if (marks.includes(DIFF_TEXT_REMOVED_MARK_NAME)) {
-			current = DIFF_TEXT_REMOVED_MARK_NAME
-		} else if (marks.includes(DIFF_TEXT_ADDED_MARK_NAME)) {
-			current = DIFF_TEXT_ADDED_MARK_NAME
-		}
-
-		if (current === DIFF_TEXT_REMOVED_MARK_NAME && previous !== current) {
-			count.removed++
-		}
-
-		if (current === DIFF_TEXT_ADDED_MARK_NAME && previous !== current) {
-			count.added++
-		}
-
-		previous = current
-
-		return false
-	})
-
-	return count
-}
diff --git a/web/i18n/locales/en/editor.json b/web/i18n/locales/en/editor.json
index bcd7cbfb..2a24e437 100644
--- a/web/i18n/locales/en/editor.json
+++ b/web/i18n/locales/en/editor.json
@@ -136,13 +136,21 @@
 			"more-indicator": "+{count}"
 		},
 		"figma": {
+			"diff": {
+				"width": "Width",
+				"height": "Height"
+			},
 			"description": "Embed Figma",
 			"placeholder": "https://www.figma.com/... + Enter",
 			"edit": "Edit URL",
-			"empty": "No Figma embed",
+			"empty": "No Figma file",
 			"iframe-title": "Figma embed"
 		},
 		"image": {
+			"diff": {
+				"image": "Image",
+				"width": "Width"
+			},
 			"description": "Upload an image",
 			"empty": "Image not uploaded",
 			"uploading": "Uploading...",
@@ -164,6 +172,9 @@
 			}
 		},
 		"mermaid": {
+			"diff": {
+				"more-lines": "+{count} more"
+			},
 			"preview": {
 				"loading": "The diagram is loading...",
 				"empty": "Add Mermaid code to see a diagram",
@@ -776,6 +787,13 @@
 					"1d": "1d"
 				}
 			},
+			"diff": {
+				"visualization": "Visualization",
+				"legend": "Legend {index}",
+				"base-threshold-color": "Base threshold colour",
+				"custom-unit": "Custom unit",
+				"size": "Size"
+			},
 			"simulation": {
 				"tooltip": "Showing simulated data until real data is available",
 				"section-title": "Simulated data",
@@ -842,7 +860,10 @@
 		"diff-change-marker": {
 			"label": "{removed} removed, {added} added",
 			"removed": "−{count}",
-			"added": "+{count}"
+			"added": "+{count}",
+			"empty": "empty",
+			"auto": "auto",
+			"pixels": "{value} px"
 		},
 		"tags": {
 			"label": "Tags",