Read MCP Apps tool results from notification params

.github/workflows/shared.yml

@@ -36,6 +36,9 @@ jobs:
       - name: Workflow script tests
         run: node --test '.github/scripts/*.test.js'
 
+      - name: MCP Apps UI script tests
+        run: node --test tests/docs_src/test_apps.test.js
+
       - name: Surface types match vendored schema
         run: |
           uv sync --group codegen --frozen

docs_src/apps/tutorial001.py

@@ -8,7 +8,7 @@
 <h1 id="now">...</h1>
 <script>
   window.addEventListener("message", (event) => {
-    const text = event.data?.result?.content?.[0]?.text;
+    const text = event.data?.params?.content?.[0]?.text;
     if (text) document.getElementById("now").textContent = text;
   });
 </script>

examples/stories/apps/server.py

@@ -18,7 +18,7 @@
 <h1 id="now">…</h1>
 <script>
   window.addEventListener("message", (event) => {
-    const text = event.data?.result?.content?.[0]?.text;
+    const text = event.data?.params?.content?.[0]?.text;
     if (text) document.getElementById("now").textContent = text;
   });
 </script>

tests/docs_src/test_apps.test.js

@@ -0,0 +1,78 @@
+const assert = require("node:assert/strict");
+const { execFileSync } = require("node:child_process");
+const path = require("node:path");
+const test = require("node:test");
+const vm = require("node:vm");
+
+const root = path.resolve(__dirname, "../..");
+const python = `
+import json
+
+import anyio
+
+from docs_src.apps import tutorial001
+from mcp import Client
+from mcp.client import advertise
+from mcp.server.apps import APP_MIME_TYPE, EXTENSION_ID
+from mcp.types import TextResourceContents
+from stories.apps.server import RESOURCE_URI, build_server
+
+
+async def main() -> None:
+    cases = []
+    for name, server, uri in (
+        ("tutorial", tutorial001.mcp, "ui://clock/app.html"),
+        ("story", build_server(), RESOURCE_URI),
+    ):
+        async with Client(server, extensions=[advertise(EXTENSION_ID, {"mimeTypes": [APP_MIME_TYPE]})]) as client:
+            resource = await client.read_resource(uri)
+            result = await client.call_tool("get_time", {})
+        content = resource.contents[0]
+        assert isinstance(content, TextResourceContents)
+        assert content.mime_type == APP_MIME_TYPE
+        cases.append({"name": name, "html": content.text, "result": result.model_dump(mode="json", by_alias=True)})
+    print(json.dumps(cases))
+
+
+anyio.run(main)
+`;
+
+const cases = JSON.parse(
+  execFileSync("uv", ["run", "--frozen", "--no-sync", "python", "-c", python], {
+    cwd: root,
+    encoding: "utf8",
+    env: {
+      ...process.env,
+      PYTHONPATH: [root, path.join(root, "examples"), process.env.PYTHONPATH]
+        .filter(Boolean)
+        .join(path.delimiter),
+    },
+  }),
+);
+
+for (const { name, html, result } of cases) {
+  test(`${name} clock shows the tool-result notification`, () => {
+    const script = html.match(/<script>([\s\S]*?)<\/script>/)?.[1];
+    assert.ok(script);
+    const clock = { textContent: "..." };
+    let onMessage;
+    vm.runInNewContext(script, {
+      window: {
+        addEventListener(type, handler) {
+          assert.equal(type, "message");
+          onMessage = handler;
+        },
+      },
+      document: {
+        getElementById(id) {
+          assert.equal(id, "now");
+          return clock;
+        },
+      },
+    });
+
+    assert.equal(typeof onMessage, "function");
+    onMessage({ data: { jsonrpc: "2.0", method: "ui/notifications/tool-result", params: result } });
+    assert.equal(clock.textContent, result.content[0].text);
+  });
+}