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Allow servers / clients to advertise extensions in the capability object (#1630)

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Tapan Chugh 2026-03-23 17:37:05 -07:00 • committed by GitHub
commit 677511b5a7
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3 changed files with 66 additions and 4 deletions
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4
packages/core/src/types/spec.types.ts
View file

@ -586,7 +586,7 @@ export interface ClientCapabilities {
* @example Extensions — UI extension with MIME type support
* {@includeCode ./examples/ClientCapabilities/extensions-ui-mime-types.json}
*/
extensions?: { [key: string]: object };
extensions?: { [key: string]: JSONObject };
}
/**
@ -703,7 +703,7 @@ export interface ServerCapabilities {
* @example Extensions — UI extension support
* {@includeCode ./examples/ServerCapabilities/extensions-ui.json}
*/
extensions?: { [key: string]: object };
extensions?: { [key: string]: JSONObject };
}
/**

12
packages/core/src/types/types.ts
View file

@ -557,7 +557,11 @@ export const ClientCapabilitiesSchema = z.object({
/**
* Present if the client supports task creation.
*/
tasks: ClientTasksCapabilitySchema.optional()
tasks: ClientTasksCapabilitySchema.optional(),
/**
* Extensions that the client supports. Keys are extension identifiers (vendor-prefix/extension-name).
*/
extensions: z.record(z.string(), JSONObjectSchema).optional()
});
export const InitializeRequestParamsSchema = BaseRequestParamsSchema.extend({
@ -635,7 +639,11 @@ export const ServerCapabilitiesSchema = z.object({
/**
* Present if the server supports task creation.
*/
tasks: ServerTasksCapabilitySchema.optional()
tasks: ServerTasksCapabilitySchema.optional(),
/**
* Extensions that the server supports. Keys are extension identifiers (vendor-prefix/extension-name).
*/
extensions: z.record(z.string(), JSONObjectSchema).optional()
});
/**

54
test/integration/test/server/mcp.test.ts
View file

@ -338,6 +338,60 @@ describe('Zod v4', () => {
message: 'Completed step 3 of 3'
});
});
/***
* Test: Extensions capability registration
*/
test('should register and advertise server extensions capability', async () => {
const mcpServer = new McpServer({
name: 'test server',
version: '1.0'
});
const client = new Client({
name: 'test client',
version: '1.0'
});
mcpServer.server.registerCapabilities({
extensions: {
'io.modelcontextprotocol/test-extension': { listChanged: true }
}
});
const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
await Promise.all([client.connect(clientTransport), mcpServer.connect(serverTransport)]);
const capabilities = client.getServerCapabilities();
expect(capabilities?.extensions).toBeDefined();
expect(capabilities?.extensions?.['io.modelcontextprotocol/test-extension']).toEqual({ listChanged: true });
});
test('should advertise client extensions capability to server', async () => {
const mcpServer = new McpServer({
name: 'test server',
version: '1.0'
});
const client = new Client(
{
name: 'test client',
version: '1.0'
},
{
capabilities: {
extensions: {
'io.modelcontextprotocol/test-extension': { streaming: true }
}
}
}
);
const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
await Promise.all([client.connect(clientTransport), mcpServer.connect(serverTransport)]);
const capabilities = mcpServer.server.getClientCapabilities();
expect(capabilities?.extensions).toBeDefined();
expect(capabilities?.extensions?.['io.modelcontextprotocol/test-extension']).toEqual({ streaming: true });
});
});
describe('ResourceTemplate', () => {