vercel/ai · error · MCPClientError

Server does not support prompts

Error message

Server does not support prompts

What it means

MCPClientError thrown by assertCapability when 'prompts/list' or 'prompts/get' is requested but the server did not advertise the `prompts` capability during the initialize handshake. The client checks `this.serverCapabilities.prompts` before dispatching the request.

Source

Thrown at packages/mcp/src/tool/mcp-client.ts:741

        if (!this.serverCapabilities.tools) {
          throw new MCPClientError({
            message: `Server does not support tools`,
          });
        }
        break;
      case 'resources/list':
      case 'resources/read':
      case 'resources/templates/list':
        if (!this.serverCapabilities.resources) {
          throw new MCPClientError({
            message: `Server does not support resources`,
          });
        }
        break;
      case 'prompts/list':
      case 'prompts/get':
        if (!this.serverCapabilities.prompts) {
          throw new MCPClientError({
            message: `Server does not support prompts`,
          });
        }
        break;
      default:
        throw new MCPClientError({
          message: `Unsupported method: ${method}`,
        });
    }
  }

  private async request<T extends z.ZodType<object>>({
    request,
    resultSchema,
    options,
  }: {
    request: Request;
    resultSchema: T;

View on GitHub (pinned to 69428b1f8b)

Solutions

  1. Confirm the server advertises `prompts` in its initialize capabilities
  2. Call and await init() before prompts/* requests
  3. Use a server that implements the prompts capability, or refactor to retrieve prompts another way (e.g. resources or a local template store)
  4. Verify you are connecting to the intended MCP server URL

Example fix

// before
const prompts = await client.listPrompts({ params: {} });

// after
await client.init();
try {
  const prompts = await client.listPrompts({ params: {} });
} catch (error) {
  if (MCPClientError.isInstance(error)) {
    // handle prompts unsupported: fall back to local prompt templates
  }
}
Defensive patterns

Strategy: try-catch

Validate before calling

await client.init();
const promptsSupported = !!initResult.capabilities?.prompts;
if (!promptsSupported) throw new Error('Server does not expose prompts');

Type guard

function isPromptsUnsupported(error: unknown): error is MCPClientError {
  return MCPClientError.isInstance(error) && error.message.includes('does not support prompts');
}

Try / catch

try {
  const prompts = await client.listPrompts({ params: {} });
} catch (error) {
  if (MCPClientError.isInstance(error) && error.message.includes('does not support prompts')) {
    // fall back to local prompt templates
  } else {
    throw error;
  }
}

Prevention

When it happens

Trigger: Calling client.listPrompts() or a prompts/get request against a server whose initialize result omits `capabilities.prompts`, or calling before init() so serverCapabilities is still {}.

Common situations: Pointing prompt-template UI code at a tools-only MCP server (most MCP servers implement tools but not prompts); server was updated/rolled back and dropped prompt support; client connected to the wrong endpoint URL.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/04c20aae72275faa. Report an issue: GitHub.