diff --git a/CHANGELOG.md b/CHANGELOG.md
index b8dfa172..abd1f25c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -67,6 +67,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   `nosniff` + restrictive CSP + attachment disposition for non-image mimes) and
   are RAM-only, bound to the instance that created them. Tunable via five
   `SANDBOX_*` env vars (see `.env.example`). (#243)
+- **Inline spoiler mark — hide text behind click-to-reveal blur.** Selected text
+  can be marked as a spoiler from a new bubble-menu toggle, or typed Discord-style
+  with the `||text||` input rule; the rendered span blurs until clicked to reveal.
+  The mark is preserved losslessly through Markdown export/import (as a raw
+  `<span data-spoiler="true">…</span>`) and on public shares. (#259)
 
 ### Changed
 
diff --git a/packages/mcp/build/lib/docmost-schema.js b/packages/mcp/build/lib/docmost-schema.js
index 6b6c221d..579a4304 100644
--- a/packages/mcp/build/lib/docmost-schema.js
+++ b/packages/mcp/build/lib/docmost-schema.js
@@ -271,6 +271,25 @@ const TextStyle = Mark.create({
         return ["span", HTMLAttributes, 0];
     },
 });
+/**
+ * Inline spoiler mark. Mirrors the @docmost/editor-ext `spoiler` mark so a
+ * document carrying a spoiler survives the MCP read -> transform -> write path
+ * (and markdown export) instead of silently dropping the unrecognized mark.
+ * packages/mcp does NOT depend on editor-ext, so the definition is kept local;
+ * it parses span[data-spoiler] and renders the same span[data-spoiler][class]
+ * the editor-ext mark emits.
+ */
+const Spoiler = Mark.create({
+    name: "spoiler",
+    // Don't bleed onto text typed at the boundary (mirrors editor-ext).
+    inclusive: false,
+    parseHTML() {
+        return [{ tag: "span[data-spoiler]" }];
+    },
+    renderHTML({ HTMLAttributes }) {
+        return ["span", { "data-spoiler": "true", class: "spoiler", ...HTMLAttributes }, 0];
+    },
+});
 /**
  * Passthrough definitions for the remaining Docmost-specific nodes.
  *
@@ -1097,6 +1116,7 @@ export const docmostExtensions = [
     // generateJSON drops <span style="color: ...">, defeating the color import.
     TextStyle,
     Comment,
+    Spoiler,
     Callout,
     Table,
     TableRow,
diff --git a/packages/mcp/build/lib/markdown-converter.js b/packages/mcp/build/lib/markdown-converter.js
index d5d47400..625650f3 100644
--- a/packages/mcp/build/lib/markdown-converter.js
+++ b/packages/mcp/build/lib/markdown-converter.js
@@ -160,6 +160,12 @@ export function convertProseMirrorToMarkdown(content) {
                                 }
                                 break;
                             }
+                            case "spoiler":
+                                // Markdown has no native spoiler syntax, so emit the same
+                                // lossless raw HTML the editor-ext turndown rule produces; the
+                                // schema's Spoiler mark parses span[data-spoiler] back on import.
+                                textContent = `<span data-spoiler="true">${textContent}</span>`;
+                                break;
                         }
                     }
                 }
diff --git a/packages/mcp/src/lib/docmost-schema.ts b/packages/mcp/src/lib/docmost-schema.ts
index 546b9844..af79a181 100644
--- a/packages/mcp/src/lib/docmost-schema.ts
+++ b/packages/mcp/src/lib/docmost-schema.ts
@@ -298,6 +298,26 @@ const TextStyle = Mark.create({
   },
 });
 
+/**
+ * Inline spoiler mark. Mirrors the @docmost/editor-ext `spoiler` mark so a
+ * document carrying a spoiler survives the MCP read -> transform -> write path
+ * (and markdown export) instead of silently dropping the unrecognized mark.
+ * packages/mcp does NOT depend on editor-ext, so the definition is kept local;
+ * it parses span[data-spoiler] and renders the same span[data-spoiler][class]
+ * the editor-ext mark emits.
+ */
+const Spoiler = Mark.create({
+  name: "spoiler",
+  // Don't bleed onto text typed at the boundary (mirrors editor-ext).
+  inclusive: false,
+  parseHTML() {
+    return [{ tag: "span[data-spoiler]" }];
+  },
+  renderHTML({ HTMLAttributes }) {
+    return ["span", { "data-spoiler": "true", class: "spoiler", ...HTMLAttributes }, 0];
+  },
+});
+
 /**
  * Passthrough definitions for the remaining Docmost-specific nodes.
  *
@@ -1194,6 +1214,7 @@ export const docmostExtensions = [
   // generateJSON drops <span style="color: ...">, defeating the color import.
   TextStyle,
   Comment,
+  Spoiler,
   Callout,
   Table,
   TableRow,
diff --git a/packages/mcp/src/lib/markdown-converter.ts b/packages/mcp/src/lib/markdown-converter.ts
index 4e35c995..36b4443d 100644
--- a/packages/mcp/src/lib/markdown-converter.ts
+++ b/packages/mcp/src/lib/markdown-converter.ts
@@ -167,6 +167,12 @@ export function convertProseMirrorToMarkdown(content: any): string {
                 }
                 break;
               }
+              case "spoiler":
+                // Markdown has no native spoiler syntax, so emit the same
+                // lossless raw HTML the editor-ext turndown rule produces; the
+                // schema's Spoiler mark parses span[data-spoiler] back on import.
+                textContent = `<span data-spoiler="true">${textContent}</span>`;
+                break;
             }
           }
         }
diff --git a/packages/mcp/test/unit/docmost-md-roundtrip.test.mjs b/packages/mcp/test/unit/docmost-md-roundtrip.test.mjs
index c80fbd53..798bac10 100644
--- a/packages/mcp/test/unit/docmost-md-roundtrip.test.mjs
+++ b/packages/mcp/test/unit/docmost-md-roundtrip.test.mjs
@@ -167,6 +167,38 @@ test("export emits comment anchors and they round-trip back to a comment mark",
   });
 });
 
+test("export emits a spoiler span and it round-trips back to a spoiler mark", () => {
+  // A small ProseMirror doc with a text run carrying a `spoiler` mark. The MCP
+  // schema mirrors the editor-ext mark, so a spoiler must survive json -> md ->
+  // json instead of being silently dropped as an unrecognized mark.
+  const doc = {
+    type: "doc",
+    content: [
+      {
+        type: "paragraph",
+        content: [
+          { type: "text", text: "plot: " },
+          {
+            type: "text",
+            text: "the butler did it",
+            marks: [{ type: "spoiler" }],
+          },
+          { type: "text", text: " end" },
+        ],
+      },
+    ],
+  };
+
+  const body = convertProseMirrorToMarkdown(doc);
+  assert.match(body, /<span data-spoiler="true">the butler did it<\/span>/);
+
+  return markdownToProseMirror(body).then((rebuilt) => {
+    const spoilered = findTextWithMark(rebuilt, "spoiler");
+    assert.ok(spoilered, "expected a text node with a spoiler mark");
+    assert.equal(spoilered.text, "the butler did it");
+  });
+});
+
 test("drawio round-trips through export and import", () => {
   const doc = {
     type: "doc",