feat: add outputSchema support for local MCP tools

CHANGELOG.md

@@ -1,3 +1,4 @@
+- Added `outputSchema` support for local MCP tools.
 - Added `appcheck:providers:list`, `appcheck:providers:get` and `appcheck:providers:set` to configure App Check attestation providers for an app.
 - Added `appcheck:apps:list` to show every app with its configured App Check providers.
 - Added web app support for Crashlytics MCP tools and prompts.

src/mcp/onemcp/onemcp_server.spec.ts

@@ -33,6 +33,7 @@
         name: "test_tool",
         description: "A test tool",
         inputSchema: { type: "object", properties: {} },
+        outputSchema: { type: "object", properties: { status: { type: "string" } } },
       };
       clientRequestStub.resolves({
         body: {
@@ -47,13 +48,14 @@
       expect(tools).to.have.length(1);
       expect(tools[0].mcp.name).to.equal("auth_test_tool");
       expect(tools[0].mcp.description).to.equal(mockMcpTool.description);
+      expect(tools[0].mcp.outputSchema).to.deep.equal(mockMcpTool.outputSchema);
       expect(tools[0].mcp._meta).to.deep.equal({
         requiresAuth: false,
         requiresProject: true,
         feature: "auth",
       });
       expect(clientRequestStub).to.have.been.calledOnce;
       expect(clientRequestStub.firstCall.args[0].headers).to.deep.include({
         "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
         "Mcp-Method": "tools/list",
       });
@@ -104,7 +106,7 @@
   });
 
   describe("callTool", () => {
     const mockContext: any = {
       projectId: "test-project",
     };
 
@@ -122,11 +124,11 @@
         body: { result: mockCallResult },
       });
 
       const result = await tool.fn({ arg: "val" }, mockContext);
 
       expect(result).to.deep.equal(mockCallResult);
       expect(ensureStub).to.have.been.calledOnceWith(
         mockContext.projectId,
         serverUrl,
         feature,
         true,
@@ -143,7 +145,7 @@
           id: 1,
         },
       });
       expect(clientRequestStub.secondCall.args[0].headers).to.deep.include({
         "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
         "Mcp-Method": "tools/call",
         "Mcp-Name": "test_tool",
@@ -178,9 +180,9 @@
         body: { result: { content: [] } },
       });
 
       await tool.fn({ region: "us-west1", query: "SELECT 1" }, mockContext);
 
       expect(clientRequestStub.secondCall.args[0].headers).to.deep.include({
         "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
         "Mcp-Method": "tools/call",
         "Mcp-Name": "execute_sql",
@@ -202,10 +204,10 @@
         body: { result: { content: [] } },
       });
 
       await tool.fn({ arg: "val" }, { ...mockContext, projectId: undefined });
 
       expect(clientRequestStub.secondCall.args[0].headers?.["x-goog-user-project"]).to.be.undefined;
       expect(clientRequestStub.secondCall.args[0].headers).to.deep.equal({
         "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
         "Mcp-Method": "tools/call",
         "Mcp-Name": "test_tool",

src/mcp/tool.spec.ts

@@ -33,12 +33,15 @@ describe("tool", () => {
         name: "test_tool",
         description: "A test tool",
         inputSchema: z.object({}),
+        outputSchema: z.object({ result: z.string() }),
       },
       testFn,
     );
 
     expect(testTool.mcp.name).to.equal("test_tool");
     expect(testTool.mcp.description).to.equal("A test tool");
+    expect(testTool.mcp.outputSchema).to.not.be.undefined;
+    expect(testTool.mcp.outputSchema.properties.result.type).to.equal("string");
     expect(testTool.fn).to.equal(testFn);
   });
 

src/mcp/tool.ts

@@ -24,6 +24,7 @@ export interface ServerTool<InputSchema extends ZodTypeAny = z.ZodAny> {
     name: string;
     description?: string;
     inputSchema: any;
+    outputSchema?: any;
     annotations?: {
       title?: string;
 
@@ -47,10 +48,11 @@ export interface ServerTool<InputSchema extends ZodTypeAny = z.ZodAny> {
   isAvailable: (ctx: McpContext) => Promise<boolean>;
 }
 
-export function tool<InputSchema extends ZodTypeAny>(
+export function tool<InputSchema extends ZodTypeAny, OutputSchema extends ZodTypeAny = z.ZodAny>(
   feature: ServerFeature,
-  options: Omit<ServerTool<InputSchema>["mcp"], "inputSchema"> & {
+  options: Omit<ServerTool<InputSchema>["mcp"], "inputSchema" | "outputSchema"> & {
     inputSchema: InputSchema;
+    outputSchema?: OutputSchema;
     isAvailable?: (ctx: McpContext) => Promise<boolean>;
   },
   fn: ServerTool<InputSchema>["fn"],
@@ -63,6 +65,13 @@ export function tool<InputSchema extends ZodTypeAny>(
       inputSchema: cleanSchema(
         z.toJSONSchema(options.inputSchema, { target: "draft-7", io: "input" }),
       ),
+      ...(options.outputSchema
+        ? {
+            outputSchema: cleanSchema(
+              z.toJSONSchema(options.outputSchema, { target: "draft-7", io: "output" }),
+            ),
+          }
+        : {}),
     },
     fn,
     isAvailable: (ctx: McpContext) => {