Accept raw zod shapes in registerAppTool as a deprecated overload

SDK v2 registerTool takes Standard JSON Schema objects (z.object(...))
and keeps a deprecated overload for the v1 raw-shape form. Mirror that
here so existing servers passing { field: z.string() } keep compiling;
the call is forwarded to the SDK, which auto-wraps the shape. Tests
exercise both forms end to end through a real McpServer and Client.

src/server/index.test.ts

@@ -7,7 +7,13 @@ import {
   getUiCapability,
   EXTENSION_ID,
 } from "./index.js";
-import type { McpServer } from "@modelcontextprotocol/server";
+import {
+  InMemoryTransport,
+  McpServer as RealMcpServer,
+  type McpServer,
+} from "@modelcontextprotocol/server";
+import { Client } from "@modelcontextprotocol/client";
+import { z } from "zod/v4";
 
 describe("registerAppTool", () => {
   it("should pass through config to server.registerTool", () => {
@@ -197,6 +203,119 @@ describe("registerAppTool", () => {
   });
 });
 
+describe("registerAppTool schema forms", () => {
+  /** Registers tools on a fresh server, then connects a client to it. */
+  async function connect(register: (server: RealMcpServer) => void) {
+    const server = new RealMcpServer({ name: "test", version: "0.0.0" });
+    register(server);
+    const client = new Client({ name: "client", version: "0.0.0" });
+    const [clientTransport, serverTransport] =
+      InMemoryTransport.createLinkedPair();
+    await server.connect(serverTransport);
+    await client.connect(clientTransport);
+    return client;
+  }
+
+  it("accepts a z.object() input schema and validates arguments", async () => {
+    const client = await connect((server) =>
+      registerAppTool(
+        server,
+        "greet",
+        {
+          inputSchema: z.object({ name: z.string() }),
+          _meta: { ui: { resourceUri: "ui://greet/view.html" } },
+        },
+        async ({ name }) => ({
+          content: [{ type: "text", text: `hello ${name}` }],
+        }),
+      ),
+    );
+
+    const { tools } = await client.listTools();
+    expect(tools).toHaveLength(1);
+    expect(tools[0].inputSchema).toMatchObject({
+      type: "object",
+      properties: { name: { type: "string" } },
+    });
+    expect(tools[0]._meta).toMatchObject({
+      ui: { resourceUri: "ui://greet/view.html" },
+      [RESOURCE_URI_META_KEY]: "ui://greet/view.html",
+    });
+
+    const result = await client.callTool({
+      name: "greet",
+      arguments: { name: "world" },
+    });
+    expect(result.content).toEqual([{ type: "text", text: "hello world" }]);
+
+    const invalid = await client.callTool({
+      name: "greet",
+      arguments: { name: 42 },
+    });
+    expect(invalid.isError).toBe(true);
+  });
+
+  it("accepts a raw zod shape (deprecated form) and wraps it with z.object()", async () => {
+    const client = await connect((server) =>
+      registerAppTool(
+        server,
+        "greet",
+        {
+          inputSchema: { name: z.string() },
+          outputSchema: { greeting: z.string() },
+          _meta: { ui: { resourceUri: "ui://greet/view.html" } },
+        },
+        async ({ name }) => ({
+          content: [{ type: "text", text: `hello ${name}` }],
+          structuredContent: { greeting: `hello ${name}` },
+        }),
+      ),
+    );
+
+    const { tools } = await client.listTools();
+    expect(tools[0].inputSchema).toMatchObject({
+      type: "object",
+      properties: { name: { type: "string" } },
+    });
+    expect(tools[0].outputSchema).toMatchObject({
+      type: "object",
+      properties: { greeting: { type: "string" } },
+    });
+
+    const result = await client.callTool({
+      name: "greet",
+      arguments: { name: "world" },
+    });
+    expect(result.structuredContent).toEqual({ greeting: "hello world" });
+
+    const invalid = await client.callTool({
+      name: "greet",
+      arguments: { name: 42 },
+    });
+    expect(invalid.isError).toBe(true);
+  });
+
+  it("accepts the raw-shape form without an input schema", async () => {
+    const client = await connect((server) =>
+      registerAppTool(
+        server,
+        "ping",
+        {
+          outputSchema: { ok: z.boolean() },
+          _meta: { ui: { resourceUri: "ui://ping/view.html" } },
+        },
+        async () => ({
+          content: [{ type: "text", text: "pong" }],
+          structuredContent: { ok: true },
+        }),
+      ),
+    );
+
+    const result = await client.callTool({ name: "ping", arguments: {} });
+    expect(result.structuredContent).toEqual({ ok: true });
+  });
+});
+
 describe("registerAppResource", () => {
   it("should register a resource with default MIME type", () => {
     let capturedName: string | undefined;

src/server/index.ts

@@ -39,31 +39,69 @@ import {
 } from "../spec.types.js";
 import { RESOURCE_URI_META_KEY, RESOURCE_MIME_TYPE } from "../constants.js";
 import type {
+  CallToolResult,
   ClientCapabilities,
+  InputRequiredResult,
   McpServer,
   ReadResourceResult,
   RegisteredTool,
   ResourceMetadata,
+  ServerContext,
   StandardSchemaWithJSON,
   ToolAnnotations,
   ToolCallback,
   ReadResourceCallback as _ReadResourceCallback,
   RegisteredResource,
 } from "@modelcontextprotocol/server";
+import type { z } from "zod/v4";
 
 // Re-exports for convenience
 export { RESOURCE_URI_META_KEY, RESOURCE_MIME_TYPE };
 export type { ResourceMetadata, ToolCallback };
 
+/**
+ * A plain `{ field: z.string() }` record accepted by the deprecated raw-shape
+ * form of {@link registerAppTool `registerAppTool`}; the SDK auto-wraps it with `z.object()`.
+ *
+ * @deprecated Wrap with `z.object({...})` instead.
+ */
+export type ZodRawShape = Record<string, z.ZodType>;
+
+/**
+ * {@link ToolCallback `ToolCallback`} variant used when `inputSchema` is a {@link ZodRawShape `ZodRawShape`}.
+ * Mirrors the callback type of the SDK's deprecated `registerTool` overload.
+ *
+ * @deprecated Wrap with `z.object({...})` instead and use {@link ToolCallback `ToolCallback`}.
+ */
+export type LegacyToolCallback<Args extends ZodRawShape | undefined> =
+  Args extends ZodRawShape
+    ? (
+        args: z.infer<z.ZodObject<Args>>,
+        ctx: ServerContext,
+      ) =>
+        | CallToolResult
+        | InputRequiredResult
+        | Promise<CallToolResult | InputRequiredResult>
+    : (
+        ctx: ServerContext,
+      ) =>
+        | CallToolResult
+        | InputRequiredResult
+        | Promise<CallToolResult | InputRequiredResult>;
+
 /**
  * Base tool configuration matching the standard MCP server tool options.
  * Extended by {@link McpUiAppToolConfig `McpUiAppToolConfig`} to add UI metadata requirements.
+ *
+ * `inputSchema`/`outputSchema` accept any Standard JSON Schema (zod v4, ArkType,
+ * Valibot, ...). A raw zod shape (`{ field: z.string() }`) is still accepted for
+ * backward compatibility but deprecated.
  */
 export interface ToolConfig {
   title?: string;
   description?: string;
-  inputSchema?: StandardSchemaWithJSON;
-  outputSchema?: StandardSchemaWithJSON;
+  inputSchema?: ZodRawShape | StandardSchemaWithJSON;
+  outputSchema?: ZodRawShape | StandardSchemaWithJSON;
   annotations?: ToolAnnotations;
   _meta?: Record<string, unknown>;
 }
@@ -217,6 +255,31 @@ export function registerAppTool<
     outputSchema?: OutputArgs;
   },
   cb: ToolCallback<InputArgs>,
+): RegisteredTool;
+/**
+ * @deprecated Wrap with `z.object({...})` instead. Raw-shape form:
+ * `inputSchema`/`outputSchema` may be a plain `{ field: z.string() }` record;
+ * the SDK auto-wraps it with `z.object()`.
+ */
+export function registerAppTool<
+  InputArgs extends ZodRawShape,
+  OutputArgs extends ZodRawShape | StandardSchemaWithJSON | undefined =
+    undefined,
+>(
+  server: Pick<McpServer, "registerTool">,
+  name: string,
+  config: McpUiAppToolConfig & {
+    inputSchema?: InputArgs;
+    outputSchema?: OutputArgs;
+  },
+  cb: LegacyToolCallback<InputArgs>,
+): RegisteredTool;
+export function registerAppTool(
+  server: Pick<McpServer, "registerTool">,
+  name: string,
+  config: McpUiAppToolConfig,
+  // Widest callback shape accepted by either overload above.
+  cb: (...args: never[]) => unknown,
 ): RegisteredTool {
   // Normalize metadata for backward compatibility:
   // - If _meta.ui.resourceUri is set, also set the legacy flat key
@@ -234,7 +297,16 @@ export function registerAppTool<
     normalizedMeta = { ...meta, ui: { ...uiMeta, resourceUri: legacyUri } };
   }
 
-  return server.registerTool(name, { ...config, _meta: normalizedMeta }, cb);
+  // The public overloads above guarantee `config`/`cb` match one of the SDK's
+  // own registerTool overloads; the union-typed implementation cannot select
+  // between them, so widen for the forwarding call.
+  return server.registerTool(
+    name,
+    { ...config, _meta: normalizedMeta } as Parameters<
+      McpServer["registerTool"]
+    >[1],
+    cb as ToolCallback<StandardSchemaWithJSON>,
+  );
 }
 
 export type McpUiReadResourceResult = ReadResourceResult & {