Use extensions capability, add prompt grouping

- Switch capability registration from experimental to extensions
- Add prompt registrations with group membership to example server
- Add prompt grouping to mixed-group test
- Update README capability section

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

Author: chughtapan

sdk/typescript/README.md

@@ -3,7 +3,7 @@
 Organize MCP tools, resources, and other primitives into named groups. This package implements the [Grouping Extension specification](../../specification/draft/grouping.mdx) as an add-on for the
 [`@modelcontextprotocol/sdk`](https://github.com/modelcontextprotocol/typescript-sdk).
 
-> **Status:** Experimental. The capability is registered under `experimental["io.modelcontextprotocol/grouping"]` until the SDK ships the `extensions` field on `ServerCapabilities`.
+> **Status:** Experimental. This is an Interest Group exploration, not an official extension.
 
 ## Install
 
@@ -197,16 +197,14 @@ The extension registers its capability at:
 
 ```json
 {
-    "experimental": {
+    "extensions": {
         "io.modelcontextprotocol/grouping": {
             "listChanged": true
         }
     }
 }
 ```
 
-When the MCP SDK adds the `extensions` field to `ServerCapabilities`, this will move to `capabilities.extensions["io.modelcontextprotocol/grouping"]`.
-
 ## Running the examples
 
 ```bash

sdk/typescript/examples/server.ts

@@ -353,7 +353,117 @@ mcpServer.registerResource(
     }
 );
 
-// TODO: add prompts once SDK registerPrompt supports _meta passthrough
+// ===== Prompts =====
+
+mcpServer.registerPrompt(
+    'email_thank_contributor',
+    {
+        description: 'Compose an email thanking someone for their recent contributions.',
+        argsSchema: {
+            name: z.string().describe('Recipient name')
+        },
+        ...metaForGroup('email')
+    },
+    async ({ name }) => ({
+        messages: [
+            {
+                role: 'user' as const,
+                content: {
+                    type: 'text' as const,
+                    text: `Compose an email thanking ${name} for their recent contributions. Keep it warm, specific, and concise.`
+                }
+            }
+        ]
+    })
+);
+
+mcpServer.registerPrompt(
+    'calendar_meeting_agenda',
+    {
+        description: 'Draft a short agenda for an upcoming meeting.',
+        argsSchema: {
+            topic: z.string().describe('Meeting topic')
+        },
+        ...metaForGroup('calendar')
+    },
+    async ({ topic }) => ({
+        messages: [
+            {
+                role: 'user' as const,
+                content: {
+                    type: 'text' as const,
+                    text: `Draft a short meeting agenda for a meeting about: ${topic}. Include goals, timeboxes, and expected outcomes.`
+                }
+            }
+        ]
+    })
+);
+
+mcpServer.registerPrompt(
+    'spreadsheets_quick_analysis',
+    {
+        description: 'Suggest a simple spreadsheet layout for tracking a metric.',
+        argsSchema: {
+            metric: z.string().describe('The metric to track')
+        },
+        ...metaForGroup('spreadsheets')
+    },
+    async ({ metric }) => ({
+        messages: [
+            {
+                role: 'user' as const,
+                content: {
+                    type: 'text' as const,
+                    text: `Suggest a simple spreadsheet layout for tracking: ${metric}. Include column headers and a brief note on how to use it.`
+                }
+            }
+        ]
+    })
+);
+
+mcpServer.registerPrompt(
+    'documents_write_outline',
+    {
+        description: 'Create an outline for a document on a topic.',
+        argsSchema: {
+            topic: z.string().describe('Document topic')
+        },
+        ...metaForGroup('documents')
+    },
+    async ({ topic }) => ({
+        messages: [
+            {
+                role: 'user' as const,
+                content: {
+                    type: 'text' as const,
+                    text: `Create a clear outline for a document about: ${topic}. Use headings and a short description under each heading.`
+                }
+            }
+        ]
+    })
+);
+
+mcpServer.registerPrompt(
+    'todos_plan_day',
+    {
+        description: 'Turn a list of tasks into a simple day plan.',
+        argsSchema: {
+            tasks: z.array(z.string()).describe('Tasks to plan')
+        },
+        ...metaForGroup('todos')
+    },
+    async ({ tasks }) => ({
+        messages: [
+            {
+                role: 'user' as const,
+                content: {
+                    type: 'text' as const,
+                    text: `Create a simple plan for the day from these tasks:\n- ${tasks.join('\n- ')}\n\nPrioritize and group similar tasks.`
+                }
+            }
+        ]
+    })
+);
 
 // --- Start server ---
 async function main() {

sdk/typescript/src/server.ts

@@ -39,8 +39,7 @@ export interface RegisteredGroup {
 /**
  * Extension that adds group support to an McpServer.
  *
- * Registers `groups/list` request handler and capability via the `experimental`
- * path (until the SDK ships the `extensions` field).
+ * Registers `groups/list` request handler and capability under `extensions`.
  */
 export class GroupingExtension {
     private _groups = new Map<string, RegisteredGroup>();
@@ -56,7 +55,7 @@ export class GroupingExtension {
         if (this._handlersInitialized) return;
 
         this._mcpServer.server.registerCapabilities({
-            experimental: {
+            extensions: {
                 [GROUPING_EXTENSION_ID]: { listChanged: true }
             }
         });

sdk/typescript/test/groups.test.ts

@@ -113,7 +113,21 @@ describe('Server Groups', () => {
             content: [{ type: 'text', text: 'hi' }]
         }));
 
-        // TODO: add prompt grouping once SDK registerPrompt supports _meta passthrough
+        // Add a prompt to the same group
+        mcpServer.registerPrompt(
+            'prompt1',
+            {
+                description: 'Test prompt 1',
+                _meta: {
+                    [GROUPS_META_KEY]: ['mixed-group']
+                }
+            },
+            async () => ({ messages: [] })
+        );
+
+        mcpServer.registerPrompt('prompt-no-group', { description: 'Prompt with no group' }, async () => ({
+            messages: []
+        }));
 
         // Add a resource to the same group
         mcpServer.registerResource(
@@ -137,8 +151,6 @@ describe('Server Groups', () => {
             })
         );
 
-        // TODO: add task-tool grouping once SDK experimental.tasks is available
-
         await Promise.all([client.connect(clientTransport), mcpServer.connect(serverTransport)]);
 
         // Verify tools
@@ -161,6 +173,15 @@ describe('Server Groups', () => {
         if (resourceNoGroup?._meta) {
             expect(resourceNoGroup._meta).not.toHaveProperty(GROUPS_META_KEY);
         }
+
+        // Verify prompts
+        const promptsResult = await client.listPrompts();
+        const prompt1 = promptsResult.prompts.find(p => p.name === 'prompt1');
+        const promptNoGroup = promptsResult.prompts.find(p => p.name === 'prompt-no-group');
+        expect(prompt1?._meta?.[GROUPS_META_KEY]).toEqual(['mixed-group']);
+        if (promptNoGroup?._meta) {
+            expect(promptNoGroup._meta).not.toHaveProperty(GROUPS_META_KEY);
+        }
     });
 
     test('should add a group to another group', async () => {