What’s New

MCP TypeScript SDK 2.0.0-alpha.1

2.0.0-alpha.1Pre-release
Major Changes

  • #1389 108f2f3 Thanks @DePasqualeOrg! - Fix error handling for unknown tools and resources per MCP spec.

    Tools: Unknown or disabled tool calls now return JSON-RPC protocol errors with code -32602 (InvalidParams) instead of CallToolResult with isError: true. Callers who checked result.isError for unknown tools should catch rejected promises instead.

    Resources: Unknown resource reads now return error code -32002 (ResourceNotFound) instead of -32602 (InvalidParams).

    Added ProtocolErrorCode.ResourceNotFound.

Minor Changes

  • #1673 462c3fc Thanks @KKonstantinov! - refactor: extract task orchestration from Protocol into TaskManager

    Breaking changes:

    • taskStore, taskMessageQueue, defaultTaskPollInterval, and maxTaskQueueSize moved from ProtocolOptions to capabilities.tasks on ClientOptions/ServerOptions

  • #1689 0784be1 Thanks @felixweinberger! - Support Standard Schema for tool and prompt schemas

    Tool and prompt registration now accepts any schema library that implements the Standard Schema spec: Zod v4, Valibot, ArkType, and others. RegisteredTool.inputSchema, RegisteredTool.outputSchema, and RegisteredPrompt.argsSchema now use StandardSchemaWithJSON (requires both ~standard.validate and ~standard.jsonSchema) instead of the Zod-specific AnySchema type.

    Zod v4 schemas continue to work unchanged — Zod v4 implements the required interfaces natively.

    import { type } from 'arktype';

server.registerTool(
    'greet',
    {
        inputSchema: type({ name: 'string' })
    },
    async ({ name }) => ({ content: [{ type: 'text', text: `Hello, ${name}!` }] })
);

    For raw JSON Schema (e.g. TypeBox output), use the new fromJsonSchema adapter:

    import { fromJsonSchema, AjvJsonSchemaValidator } from '@modelcontextprotocol/core';

server.registerTool(
    'greet',
    {
        inputSchema: fromJsonSchema({ type: 'object', properties: { name: { type: 'string' } } }, new AjvJsonSchemaValidator())
    },
    handler
);

    Breaking changes:

    • experimental.tasks.getTaskResult() no longer accepts a resultSchema parameter. Returns GetTaskPayloadResult (a loose Result); cast to the expected type at the call site.
    • Removed unused exports from @modelcontextprotocol/core: SchemaInput, schemaToJson, parseSchemaAsync, getSchemaShape, getSchemaDescription, isOptionalSchema, unwrapOptionalSchema. Use the new standardSchemaToJsonSchema and validateStandardSchema instead.
    • completable() remains Zod-specific (it relies on Zod's .shape introspection).
Patch Changes

  • #1758 e86b183 Thanks @KKonstantinov! - tasks - disallow requesting a null TTL

  • #1363 0a75810 Thanks @DevJanderson! - Fix ReDoS vulnerability in UriTemplate regex patterns (CVE-2026-0621)

  • #1372 3466a9e Thanks @mattzcarey! - missing change for fix(client): replace body.cancel() with text() to prevent hanging

  • #1824 fcde488 Thanks @felixweinberger! - Drop zod from peerDependencies (kept as direct dependency)

    Since Standard Schema support landed, zod is purely an internal runtime dependency used for protocol message parsing. User-facing schemas (registerTool, registerPrompt) accept any Standard Schema library. zod remains in dependencies and auto-installs; users no longer need to install it alongside the SDK.

  • #1761 01954e6 Thanks @felixweinberger! - Convert remaining capability-assertion throws to SdkError(SdkErrorCode.CapabilityNotSupported, ...). Follow-up to #1454 which missed Client.assertCapability(), the task capability helpers in experimental/tasks/helpers.ts, and the sampling/elicitation capability checks in experimental/tasks/server.ts.

  • #1433 78bae74 Thanks @codewithkenzo! - Fix transport errors being silently swallowed by adding missing onerror callback invocations before all createJsonErrorResponse calls in WebStandardStreamableHTTPServerTransport. This ensures errors like parse failures, invalid headers, and session validation errors are properly reported via the onerror callback.

  • #1660 689148d Thanks @rechedev9! - fix(server): propagate negotiated protocol version to transport in _oninitialize

  • #1568 f1ade75 Thanks @stakeswky! - Handle stdout errors (e.g. EPIPE) in StdioServerTransport gracefully instead of crashing. When the client disconnects abruptly, the transport now catches the stdout error, surfaces it via onerror, and closes.

  • #1419 dcf708d Thanks @KKonstantinov! - remove deprecated .tool, .prompt, .resource method signatures

  • #1388 f66a55b Thanks @mattzcarey! - reverting application/json in notifications

  • #1534 69a0626 Thanks @josefaidt! - remove npm references, use pnpm

  • #1534 69a0626 Thanks @josefaidt! - clean up package manager usage, all pnpm

  • #1419 dcf708d Thanks @KKonstantinov! - deprecated .tool, .prompt, .resource method removal

  • #1279 71ae3ac Thanks @KKonstantinov! - Initial 2.0.0-alpha.0 client and server package

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