diff --git a/packages/review/src/review-api/agent-client.test.ts b/packages/review/src/review-api/agent-client.test.ts
index 2225a634c..9a791c65b 100644
--- a/packages/review/src/review-api/agent-client.test.ts
+++ b/packages/review/src/review-api/agent-client.test.ts
@@ -207,6 +207,12 @@ it("serves MCP framing without stdout diagnostics and returns host errors as too
     });
     const list = await request(2, "tools/list", {});
     ListToolsResultSchema.parse(list.result);
+    // The Anthropic API rejects these at the top level of a tool input schema.
+    expect(
+      list.result.tools.filter((tool: AuthoringTool) =>
+        ["anyOf", "oneOf", "allOf"].some((key) => key in tool.inputSchema),
+      ),
+    ).toEqual([]);
     expect(
       list.result.tools.find(
         (tool: AuthoringTool) => tool.name === "session_edit",
diff --git a/packages/review/src/review-api/authoring-tools.ts b/packages/review/src/review-api/authoring-tools.ts
index 50880d34f..eb4c208eb 100644
--- a/packages/review/src/review-api/authoring-tools.ts
+++ b/packages/review/src/review-api/authoring-tools.ts
@@ -17,6 +17,19 @@ export function authoringTools(
   const review = { reviewId: id };
   const version = z.number().int().nonnegative().optional();
 
+  // Anthropic rejects a top-level union, so publish one object; the host validates the union.
+  const [image, trace, map] = uploadSchema.options;
+
+  const uploadInput = z
+    .strictObject({
+      ...image.shape,
+      ...trace.shape,
+      ...map.shape,
+      kind: z.enum(["image", "trace", "map"]),
+    })
+    .partial()
+    .required({ id: true, repositoryId: true, kind: true });
+
   const read = (name: keyof typeof readQuerySchemas) =>
     z.strictObject({ ...review, ...readQuerySchemas[name].shape });
 
@@ -162,8 +175,8 @@ export function authoringTools(
     ),
     tool(
       "upload",
-      "Retain an image, trace or software map for use in a review. Reusing an upload ID requires identical content; rejected uploads are not saved.",
-      uploadSchema,
+      'Retain an image, trace or software map for use in a review. kind:"image" takes base64; kind:"trace" takes trace; kind:"map" takes pins, side and model. Reusing an upload ID requires identical content; rejected uploads are not saved.',
+      uploadInput,
       "POST",
       "/resources",
     ),