Add _meta support to registerPrompt

Prompts were the only primitive missing _meta passthrough. This adds
_meta to RegisteredPrompt, _createRegisteredPrompt, registerPrompt,
and the prompts/list handler, mirroring the existing tool pattern.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: chughtapan

packages/server/src/server/mcp.ts

@@ -538,7 +538,8 @@ export class McpServer {
                             name,
                             title: prompt.title,
                             description: prompt.description,
-                            arguments: prompt.argsSchema ? promptArgumentsFromSchema(prompt.argsSchema) : undefined
+                            arguments: prompt.argsSchema ? promptArgumentsFromSchema(prompt.argsSchema) : undefined,
+                            _meta: prompt._meta
                         };
                     })
             })
@@ -707,6 +708,7 @@ export class McpServer {
         title: string | undefined,
         description: string | undefined,
         argsSchema: AnySchema | undefined,
+        _meta: Record<string, unknown> | undefined,
         callback: PromptCallback<AnySchema | undefined>
     ): RegisteredPrompt {
         // Track current schema and callback for handler regeneration
@@ -717,6 +719,7 @@ export class McpServer {
             title,
             description,
             argsSchema,
+            _meta,
             handler: createPromptHandler(name, argsSchema, callback),
             enabled: true,
             disable: () => registeredPrompt.update({ enabled: false }),
@@ -729,6 +732,7 @@ export class McpServer {
                 }
                 if (updates.title !== undefined) registeredPrompt.title = updates.title;
                 if (updates.description !== undefined) registeredPrompt.description = updates.description;
+                if (updates._meta !== undefined) registeredPrompt._meta = updates._meta;
 
                 // Track if we need to regenerate the handler
                 let needsHandlerRegen = false;
@@ -929,20 +933,22 @@ export class McpServer {
             title?: string;
             description?: string;
             argsSchema?: Args;
+            _meta?: Record<string, unknown>;
         },
         cb: PromptCallback<Args>
     ): RegisteredPrompt {
         if (this._registeredPrompts[name]) {
             throw new Error(`Prompt ${name} is already registered`);
         }
 
-        const { title, description, argsSchema } = config;
+        const { title, description, argsSchema, _meta } = config;
 
         const registeredPrompt = this._createRegisteredPrompt(
             name,
             title,
             description,
             argsSchema,
+            _meta,
             cb as PromptCallback<AnySchema | undefined>
         );
 
@@ -1231,6 +1237,7 @@ export type RegisteredPrompt = {
     title?: string;
     description?: string;
     argsSchema?: AnySchema;
+    _meta?: Record<string, unknown>;
     /** @hidden */
     handler: PromptHandler;
     enabled: boolean;
@@ -1241,6 +1248,7 @@ export type RegisteredPrompt = {
         title?: string;
         description?: string;
         argsSchema?: Args;
+        _meta?: Record<string, unknown>;
         callback?: PromptCallback<Args>;
         enabled?: boolean;
     }): void;

test/integration/test/server/mcp.test.ts

@@ -4113,6 +4113,99 @@ describe('Zod v4', () => {
                 }
             ]);
         });
+
+        /***
+         * Test: Prompt Registration with _meta field
+         */
+        test('should register prompt with _meta field and include it in list response', async () => {
+            const mcpServer = new McpServer({
+                name: 'test server',
+                version: '1.0'
+            });
+            const client = new Client({
+                name: 'test client',
+                version: '1.0'
+            });
+
+            const metaData = {
+                author: 'test-author',
+                version: '1.2.3',
+                category: 'utility',
+                tags: ['test', 'example']
+            };
+
+            mcpServer.registerPrompt(
+                'test-with-meta',
+                {
+                    description: 'A prompt with _meta field',
+                    _meta: metaData
+                },
+                async () => ({
+                    messages: [
+                        {
+                            role: 'assistant',
+                            content: {
+                                type: 'text',
+                                text: 'Test response'
+                            }
+                        }
+                    ]
+                })
+            );
+
+            const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+
+            await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
+
+            const result = await client.request({ method: 'prompts/list' });
+
+            expect(result.prompts).toHaveLength(1);
+            expect(result.prompts[0]!.name).toBe('test-with-meta');
+            expect(result.prompts[0]!.description).toBe('A prompt with _meta field');
+            expect(result.prompts[0]!._meta).toEqual(metaData);
+        });
+
+        /***
+         * Test: Prompt Registration without _meta field should have undefined _meta
+         */
+        test('should register prompt without _meta field and have undefined _meta in response', async () => {
+            const mcpServer = new McpServer({
+                name: 'test server',
+                version: '1.0'
+            });
+            const client = new Client({
+                name: 'test client',
+                version: '1.0'
+            });
+
+            mcpServer.registerPrompt(
+                'test-without-meta',
+                {
+                    description: 'A prompt without _meta field'
+                },
+                async () => ({
+                    messages: [
+                        {
+                            role: 'assistant',
+                            content: {
+                                type: 'text',
+                                text: 'Test response'
+                            }
+                        }
+                    ]
+                })
+            );
+
+            const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+
+            await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
+
+            const result = await client.request({ method: 'prompts/list' });
+
+            expect(result.prompts).toHaveLength(1);
+            expect(result.prompts[0]!.name).toBe('test-without-meta');
+            expect(result.prompts[0]!._meta).toBeUndefined();
+        });
     });
 
     describe('Tool title precedence', () => {