feat(compat): registerTool/registerPrompt accept raw Zod shape, auto-wrap with z.object()

.changeset/register-rawshape-compat.md

@@ -0,0 +1,6 @@
+---
+'@modelcontextprotocol/core': patch
+'@modelcontextprotocol/server': patch
+---
+
+`registerTool`/`registerPrompt` accept a raw Zod shape (`{ field: z.string() }`) for `inputSchema`/`outputSchema`/`argsSchema` in addition to a wrapped Standard Schema. Raw shapes are auto-wrapped with `z.object()`. The raw-shape overloads are `@deprecated`; prefer wrapping with `z.object()`.

packages/core/src/util/standardSchema.ts

@@ -6,6 +6,8 @@
 
 /* eslint-disable @typescript-eslint/no-namespace */
 
+import * as z from 'zod/v4';
+
 // Standard Schema interfaces — vendored from https://standardschema.dev (spec v1, Jan 2025)
 
 export interface StandardTypedV1<Input = unknown, Output = Input> {
@@ -136,6 +138,45 @@ export function isStandardSchemaWithJSON(schema: unknown): schema is StandardSch
     return isStandardJSONSchema(schema) && isStandardSchema(schema);
 }
 
+function isZodSchema(v: unknown): v is z.ZodType {
+    if (typeof v !== 'object' || v === null) return false;
+    if ('_def' in v) return true;
+    return isStandardSchema(v) && (v as StandardSchemaV1)['~standard'].vendor === 'zod';
+}
+
+/**
+ * Detects a "raw shape" — a plain object whose values are Zod field schemas,
+ * e.g. `{ name: z.string() }`. Powers the auto-wrap in
+ * {@linkcode normalizeRawShapeSchema}, which wraps with `z.object()`, so only
+ * Zod values are supported.
+ *
+ * @internal
+ */
+export function isZodRawShape(obj: unknown): obj is Record<string, z.ZodType> {
+    if (typeof obj !== 'object' || obj === null) return false;
+    if (isStandardSchema(obj)) return false;
+    // [].every() is true, so an empty object is a valid raw shape (matches v1).
+    return Object.values(obj).every(v => isZodSchema(v));
+}
+
+/**
+ * Accepts either a {@linkcode StandardSchemaWithJSON} or a raw Zod shape
+ * `{ field: z.string() }` and returns a {@linkcode StandardSchemaWithJSON}.
+ * Raw shapes are wrapped with `z.object()` so the rest of the pipeline sees a
+ * uniform schema type; already-wrapped schemas pass through unchanged.
+ *
+ * @internal
+ */
+export function normalizeRawShapeSchema(
+    schema: StandardSchemaWithJSON | Record<string, z.ZodType> | undefined
+): StandardSchemaWithJSON | undefined {
+    if (schema === undefined) return undefined;
+    if (isZodRawShape(schema)) {
+        return z.object(schema) as StandardSchemaWithJSON;
+    }
+    return schema;
+}
+
 // JSON Schema conversion
 
 /**

packages/core/test/util/standardSchema.test.ts

@@ -1,6 +1,37 @@
 import * as z from 'zod/v4';
 
-import { standardSchemaToJsonSchema } from '../../src/util/standardSchema.js';
+import { isZodRawShape, normalizeRawShapeSchema, standardSchemaToJsonSchema } from '../../src/util/standardSchema.js';
+
+describe('isZodRawShape', () => {
+    test('treats empty object as a raw shape (matches v1)', () => {
+        expect(isZodRawShape({})).toBe(true);
+    });
+    test('detects raw shape with zod fields', () => {
+        expect(isZodRawShape({ a: z.string() })).toBe(true);
+    });
+    test('rejects a Standard Schema instance', () => {
+        expect(isZodRawShape(z.object({ a: z.string() }))).toBe(false);
+    });
+    test('rejects a shape with non-Zod Standard Schema fields', () => {
+        const nonZod = { '~standard': { version: 1, vendor: 'arktype', validate: () => ({ value: 'x' }) } };
+        expect(isZodRawShape({ a: nonZod })).toBe(false);
+    });
+});
+
+describe('normalizeRawShapeSchema', () => {
+    test('wraps empty raw shape into z.object({})', () => {
+        const wrapped = normalizeRawShapeSchema({});
+        expect(wrapped).toBeDefined();
+        expect(standardSchemaToJsonSchema(wrapped!, 'input').type).toBe('object');
+    });
+    test('passes through an already-wrapped Standard Schema unchanged', () => {
+        const schema = z.object({ a: z.string() });
+        expect(normalizeRawShapeSchema(schema)).toBe(schema);
+    });
+    test('returns undefined for undefined input', () => {
+        expect(normalizeRawShapeSchema(undefined)).toBeUndefined();
+    });
+});
 
 describe('standardSchemaToJsonSchema', () => {
     test('emits type:object for plain z.object schemas', () => {

packages/server/src/server/mcp.ts

@@ -30,6 +30,7 @@ import type {
 import {
     assertCompleteRequestPrompt,
     assertCompleteRequestResourceTemplate,
+    normalizeRawShapeSchema,
     promptArgumentsFromStandardSchema,
     ProtocolError,
     ProtocolErrorCode,
@@ -39,6 +40,7 @@ import {
     validateStandardSchema
 } from '@modelcontextprotocol/core';
 
+import type * as z from 'zod/v4';
 import type { ToolTaskHandler } from '../experimental/tasks/interfaces.js';
 import { ExperimentalMcpServerTasks } from '../experimental/tasks/mcpServer.js';
 import { getCompleter, isCompletable } from './completable.js';
@@ -873,6 +875,31 @@ export class McpServer {
             _meta?: Record<string, unknown>;
         },
         cb: ToolCallback<InputArgs>
+    ): RegisteredTool;
+    /** @deprecated Wrap with `z.object({...})` instead. Raw-shape form: `inputSchema`/`outputSchema` may be a plain `{ field: z.string() }` record; it is auto-wrapped with `z.object()`. */
+    registerTool<InputArgs extends ZodRawShape, OutputArgs extends ZodRawShape | StandardSchemaWithJSON | undefined = undefined>(
+        name: string,
+        config: {
+            title?: string;
+            description?: string;
+            inputSchema?: InputArgs;
+            outputSchema?: OutputArgs;
+            annotations?: ToolAnnotations;
+            _meta?: Record<string, unknown>;
+        },
+        cb: LegacyToolCallback<InputArgs>
+    ): RegisteredTool;
+    registerTool(
+        name: string,
+        config: {
+            title?: string;
+            description?: string;
+            inputSchema?: StandardSchemaWithJSON | ZodRawShape;
+            outputSchema?: StandardSchemaWithJSON | ZodRawShape;
+            annotations?: ToolAnnotations;
+            _meta?: Record<string, unknown>;
+        },
+        cb: ToolCallback<StandardSchemaWithJSON | undefined> | LegacyToolCallback<ZodRawShape>
     ): RegisteredTool {
         if (this._registeredTools[name]) {
             throw new Error(`Tool ${name} is already registered`);
@@ -884,8 +911,8 @@ export class McpServer {
             name,
             title,
             description,
-            inputSchema,
-            outputSchema,
+            normalizeRawShapeSchema(inputSchema),
+            normalizeRawShapeSchema(outputSchema),
             annotations,
             { taskSupport: 'forbidden' },
             _meta,
@@ -928,6 +955,27 @@ export class McpServer {
             _meta?: Record<string, unknown>;
         },
         cb: PromptCallback<Args>
+    ): RegisteredPrompt;
+    /** @deprecated Wrap with `z.object({...})` instead. Raw-shape form: `argsSchema` may be a plain `{ field: z.string() }` record; it is auto-wrapped with `z.object()`. */
+    registerPrompt<Args extends ZodRawShape>(
+        name: string,
+        config: {
+            title?: string;
+            description?: string;
+            argsSchema?: Args;
+            _meta?: Record<string, unknown>;
+        },
+        cb: LegacyPromptCallback<Args>
+    ): RegisteredPrompt;
+    registerPrompt(
+        name: string,
+        config: {
+            title?: string;
+            description?: string;
+            argsSchema?: StandardSchemaWithJSON | ZodRawShape;
+            _meta?: Record<string, unknown>;
+        },
+        cb: PromptCallback<StandardSchemaWithJSON> | LegacyPromptCallback<ZodRawShape>
     ): RegisteredPrompt {
         if (this._registeredPrompts[name]) {
             throw new Error(`Prompt ${name} is already registered`);
@@ -939,7 +987,7 @@ export class McpServer {
             name,
             title,
             description,
-            argsSchema,
+            normalizeRawShapeSchema(argsSchema),
             cb as PromptCallback<StandardSchemaWithJSON | undefined>,
             _meta
         );
@@ -1062,6 +1110,26 @@ export class ResourceTemplate {
     }
 }
 
+/**
+ * A plain record of Zod field schemas, e.g. `{ name: z.string() }`. Accepted by
+ * `registerTool`/`registerPrompt` as a shorthand; auto-wrapped with `z.object()`.
+ * Zod schemas only — `z.object()` cannot wrap other Standard Schema libraries.
+ */
+export type ZodRawShape = Record<string, z.ZodType>;
+
+/** Infers the parsed-output type of a {@linkcode ZodRawShape}. */
+export type InferRawShape<S extends ZodRawShape> = { [K in keyof S]: z.output<S[K]> };
+
+/** {@linkcode ToolCallback} variant used when `inputSchema` is a {@linkcode ZodRawShape}. */
+export type LegacyToolCallback<Args extends ZodRawShape | undefined> = Args extends ZodRawShape
+    ? (args: InferRawShape<Args>, ctx: ServerContext) => CallToolResult | Promise<CallToolResult>
+    : (ctx: ServerContext) => CallToolResult | Promise<CallToolResult>;
+
+/** {@linkcode PromptCallback} variant used when `argsSchema` is a {@linkcode ZodRawShape}. */
+export type LegacyPromptCallback<Args extends ZodRawShape | undefined> = Args extends ZodRawShape
+    ? (args: InferRawShape<Args>, ctx: ServerContext) => GetPromptResult | Promise<GetPromptResult>
+    : (ctx: ServerContext) => GetPromptResult | Promise<GetPromptResult>;
+
 export type BaseToolCallback<
     SendResultT extends Result,
     Ctx extends ServerContext,

packages/server/test/server/mcp.compat.test.ts

@@ -0,0 +1,101 @@
+import type { JSONRPCMessage } from '@modelcontextprotocol/core';
+import { InMemoryTransport, isStandardSchema, LATEST_PROTOCOL_VERSION } from '@modelcontextprotocol/core';
+import { describe, expect, it, vi } from 'vitest';
+import * as z from 'zod/v4';
+import { McpServer } from '../../src/index.js';
+
+describe('registerTool/registerPrompt accept raw Zod shape (auto-wrapped)', () => {
+    it('registerTool accepts a raw shape for inputSchema and auto-wraps it', () => {
+        const server = new McpServer({ name: 't', version: '1.0.0' });
+
+        server.registerTool('a', { inputSchema: { x: z.number() } }, async ({ x }) => ({
+            content: [{ type: 'text' as const, text: String(x) }]
+        }));
+        server.registerTool('b', { inputSchema: { y: z.number() } }, async ({ y }) => ({
+            content: [{ type: 'text' as const, text: String(y) }]
+        }));
+
+        const tools = (server as unknown as { _registeredTools: Record<string, { inputSchema?: unknown }> })._registeredTools;
+        expect(Object.keys(tools)).toEqual(['a', 'b']);
+        // raw shape was wrapped into a Standard Schema (z.object)
+        expect(isStandardSchema(tools['a']?.inputSchema)).toBe(true);
+    });
+
+    it('registerTool accepts a raw shape for outputSchema and auto-wraps it', () => {
+        const server = new McpServer({ name: 't', version: '1.0.0' });
+
+        server.registerTool('out', { inputSchema: { n: z.number() }, outputSchema: { result: z.string() } }, async ({ n }) => ({
+            content: [{ type: 'text' as const, text: String(n) }],
+            structuredContent: { result: String(n) }
+        }));
+
+        const tools = (server as unknown as { _registeredTools: Record<string, { outputSchema?: unknown }> })._registeredTools;
+        expect(isStandardSchema(tools['out']?.outputSchema)).toBe(true);
+    });
+
+    it('registerTool with z.object() inputSchema also works (passthrough, no auto-wrap)', () => {
+        const server = new McpServer({ name: 't', version: '1.0.0' });
+
+        server.registerTool('c', { inputSchema: z.object({ x: z.number() }) }, async ({ x }) => ({
+            content: [{ type: 'text' as const, text: String(x) }]
+        }));
+
+        const tools = (server as unknown as { _registeredTools: Record<string, { inputSchema?: unknown }> })._registeredTools;
+        expect(isStandardSchema(tools['c']?.inputSchema)).toBe(true);
+    });
+
+    it('registerPrompt accepts a raw shape for argsSchema', () => {
+        const server = new McpServer({ name: 't', version: '1.0.0' });
+
+        server.registerPrompt('p', { argsSchema: { topic: z.string() } }, async ({ topic }) => ({
+            messages: [{ role: 'user' as const, content: { type: 'text' as const, text: topic } }]
+        }));
+
+        const prompts = (server as unknown as { _registeredPrompts: Record<string, { argsSchema?: unknown }> })._registeredPrompts;
+        expect(Object.keys(prompts)).toContain('p');
+        expect(isStandardSchema(prompts['p']?.argsSchema)).toBe(true);
+    });
+
+    it('callback receives validated, typed args end-to-end via tools/call', async () => {
+        const server = new McpServer({ name: 't', version: '1.0.0' });
+
+        let received: { x: number } | undefined;
+        server.registerTool('echo', { inputSchema: { x: z.number() } }, async args => {
+            received = args;
+            return { content: [{ type: 'text' as const, text: String(args.x) }] };
+        });
+
+        const [client, srv] = InMemoryTransport.createLinkedPair();
+        await server.connect(srv);
+        await client.start();
+
+        const responses: JSONRPCMessage[] = [];
+        client.onmessage = m => responses.push(m);
+
+        await client.send({
+            jsonrpc: '2.0',
+            id: 1,
+            method: 'initialize',
+            params: {
+                protocolVersion: LATEST_PROTOCOL_VERSION,
+                capabilities: {},
+                clientInfo: { name: 'c', version: '1.0.0' }
+            }
+        } as JSONRPCMessage);
+        await client.send({ jsonrpc: '2.0', method: 'notifications/initialized' } as JSONRPCMessage);
+        await client.send({
+            jsonrpc: '2.0',
+            id: 2,
+            method: 'tools/call',
+            params: { name: 'echo', arguments: { x: 7 } }
+        } as JSONRPCMessage);
+
+        await vi.waitFor(() => expect(responses.some(r => 'id' in r && r.id === 2)).toBe(true));
+
+        expect(received).toEqual({ x: 7 });
+        const result = responses.find(r => 'id' in r && r.id === 2) as { result?: { content: Array<{ text: string }> } };
+        expect(result.result?.content[0]?.text).toBe('7');
+
+        await server.close();
+    });
+});