diff --git a/packages/junior/src/chat/slack/tool-support/canvas/api.ts b/packages/junior/src/chat/slack/tool-support/canvas/api.ts
index f5357a3cb8..703985309c 100644
--- a/packages/junior/src/chat/slack/tool-support/canvas/api.ts
+++ b/packages/junior/src/chat/slack/tool-support/canvas/api.ts
@@ -9,6 +9,7 @@ import {
   withSlackRetries,
 } from "@/chat/slack/client";
 import { extractCanvasId } from "@/chat/slack/canvas-references";
+import { canvasBodyToMarkdown } from "@/chat/slack/tool-support/canvas/html";
 import {
   normalizeCanvasMarkdown,
   type CanvasMarkdownNormalization,
@@ -190,10 +191,10 @@ function isCanvasFile(file: NonNullable<FilesInfoResponse["file"]>): boolean {
 }
 
 /**
- * Read a Slack canvas the bot has access to and return its raw downloadable
- * content. Slack does not expose a structured canvas-read API, so we fetch
- * file metadata via `files.info` and download the canvas body via the private
- * file URL with the bot token.
+ * Read a Slack canvas the bot has access to and return its body as Markdown.
+ * Slack does not expose a structured canvas-read API, so we fetch file
+ * metadata via `files.info` and download the canvas body via the private file
+ * URL with the bot token.
  */
 export async function readCanvas(
   canvasIdOrUrl: string,
@@ -236,13 +237,14 @@ export async function readCanvas(
   }
 
   const buffer = await downloadPrivateSlackFile(downloadUrl);
+  const title = file.title ?? file.name;
   return {
     canvasId,
-    title: file.title ?? file.name,
+    title,
     permalink: file.permalink,
     mimetype: file.mimetype,
     filetype: file.filetype,
-    content: buffer.toString("utf-8"),
+    content: canvasBodyToMarkdown(buffer.toString("utf-8"), title),
     byteLength: buffer.byteLength,
   };
 }
diff --git a/packages/junior/src/chat/slack/tool-support/canvas/html.ts b/packages/junior/src/chat/slack/tool-support/canvas/html.ts
new file mode 100644
index 0000000000..318be01810
--- /dev/null
+++ b/packages/junior/src/chat/slack/tool-support/canvas/html.ts
@@ -0,0 +1,63 @@
+import { NodeHtmlMarkdown } from "node-html-markdown";
+
+// Slack serves canvas downloads as Quip HTML, with links as `<lnk href>`.
+const canvasHtmlConverter = new NodeHtmlMarkdown(
+  {
+    bulletMarker: "-",
+    codeBlockStyle: "fenced",
+    maxConsecutiveNewlines: 2,
+  },
+  {
+    lnk: ({ node }) => ({
+      prefix: "[",
+      postfix: `](${node.getAttribute("href") ?? ""})`,
+    }),
+  },
+);
+
+// Quip marks a checklist as `data-section-style="7"` and a done item with the
+// `checked` class. Canvas writes take `- [ ]` and `- [x]`.
+const listItemTranslator = canvasHtmlConverter.translators.get("li");
+canvasHtmlConverter.translators.set("li", (context) => {
+  const config =
+    typeof listItemTranslator === "function"
+      ? listItemTranslator(context)
+      : listItemTranslator;
+  const section = context.node.closest("[data-section-style]");
+  if (section?.getAttribute("data-section-style") !== "7") {
+    return config;
+  }
+  const checkbox = context.node.classList.contains("checked") ? "[x] " : "[ ] ";
+  return { ...config, prefix: `${config?.prefix ?? ""}${checkbox}` };
+});
+
+// A leading HTML start tag, not a Markdown autolink such as `<https://...>`.
+const leadingHtmlTag = /^\s*<[a-z][a-z0-9-]*[\s/>]/i;
+
+/**
+ * Convert a downloaded canvas body to Markdown. Canvas writes take Markdown,
+ * so an HTML body passed back unchanged renders as escaped HTML text.
+ */
+export function canvasBodyToMarkdown(body: string, title?: string): string {
+  if (!leadingHtmlTag.test(body)) {
+    return body;
+  }
+  const markdown = canvasHtmlConverter.translate(body).trim();
+  // The export starts with the canvas title as an `h1`. Slack keeps that
+  // heading across a body replace, so writing it back would show it twice.
+  // Convert the title the same way so Markdown escapes match.
+  const titleHeading = title
+    ? canvasHtmlConverter.translate(`<h1>${escapeHtml(title)}</h1>`).trim()
+    : undefined;
+  if (titleHeading && markdown.split("\n", 1)[0] === titleHeading) {
+    return markdown.slice(titleHeading.length).trimStart();
+  }
+  return markdown;
+}
+
+function escapeHtml(text: string): string {
+  return text
+    .replaceAll("&", "&amp;")
+    .replaceAll("<", "&lt;")
+    .replaceAll(">", "&gt;");
+}
diff --git a/packages/junior/tests/integration/slack-canvas-edit.test.ts b/packages/junior/tests/integration/slack-canvas-edit.test.ts
index bba36d70fe..956cd5371d 100644
--- a/packages/junior/tests/integration/slack-canvas-edit.test.ts
+++ b/packages/junior/tests/integration/slack-canvas-edit.test.ts
@@ -21,11 +21,15 @@ function createState(): ToolState {
   };
 }
 
-function queueCanvasRead(canvasId: string, body: string): void {
+function queueCanvasRead(
+  canvasId: string,
+  body: string,
+  title = "Reference Canvas",
+): void {
   queueSlackApiResponse("files.info", {
     body: filesInfoOk({
       fileId: canvasId,
-      title: "Reference Canvas",
+      title,
       permalink: `https://sentry.slack.com/docs/T000/${canvasId}`,
       urlPrivate: `https://files.slack.com/files-pri/T000-${canvasId}/canvas.md`,
     }),
@@ -84,6 +88,50 @@ describe("Slack canvas file-like tools", () => {
     expect((result as { diff: string }).diff).toContain("+3 New summary");
   });
 
+  it("edits a canvas served as Quip HTML and writes Markdown back", async () => {
+    queueCanvasRead(
+      "F0PREVIOUS",
+      '<div class="quip-canvas-content"><h1 id="temp:C:T">Q4 [draft] notes_v1 &amp; more</h1>' +
+        '<h2 id="temp:C:A">Rows</h2>' +
+        '<div data-section-style="5"><ul id="temp:C:B"><li id="temp:C:C">' +
+        '<span><lnk href="https://linear.app/getsentry/issue/NET-625">NET-625</lnk>' +
+        " — <code>Docs</code> fix</span><br/></li></ul></div>" +
+        '<div data-section-style="7"><ul id="temp:C:E">' +
+        '<li id="temp:C:F" class="checked"><span>Done</span><br/></li>' +
+        '<li id="temp:C:G" class=""><span>Open</span><br/></li></ul></div>' +
+        '<p id="temp:C:D" class="line">Old summary</p></div>',
+      "Q4 [draft] notes_v1 & more",
+    );
+    queueSlackApiResponse("canvases.edit", {
+      body: canvasesEditOk(),
+    });
+    const tool = createSlackCanvasEditTool(createState());
+
+    if (typeof tool.execute !== "function") {
+      throw new Error("slackCanvasEdit execute function missing");
+    }
+
+    await tool.execute(
+      {
+        canvas: "F0PREVIOUS",
+        edits: [{ old_text: "Old summary", new_text: "New summary" }],
+      },
+      {} as never,
+    );
+
+    const editCalls = getCapturedSlackApiCalls("canvases.edit");
+    expect(editCalls[0]?.params).toMatchObject({
+      changes: [
+        {
+          document_content: {
+            markdown:
+              "## Rows\n\n- [NET-625](https://linear.app/getsentry/issue/NET-625) — `Docs` fix\n\n- [x] Done\n- [ ] Open\n\nNew summary",
+          },
+        },
+      ],
+    });
+  });
+
   it("applies multiple edits against the original canvas content in one write", async () => {
     queueCanvasRead(
       "F0PREVIOUS",