This week in Claude Code · Apr 26, 2026

MCP TypeScript SDK Alpha 2 Lands with Export Fixes Across All Packages

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TLDR;

The MCP TypeScript SDK dropped two waves of 2.0.0 alpha releases this week. Alpha.1 introduced breaking changes including spec-compliant error codes for unknown tools, removal of WebSocketClientTransport, and a new Fastify middleware adapter. Alpha.2 follows immediately with a tsdown exports resolution fix across all six packages (server, client, node, express, hono, fastify). On the stable 1.x track, v1.28.0 and v1.29.0 deliver OAuth improvements, a disallowed null TTL, and a missing ResourceSchema size field. If you are building MCP servers, audit your error-handling logic for the -32602 code change and drop any WebSocket transport usage before promoting to production.

MCP Ecosystem

MCP TypeScript SDK 2.0.0-alpha.2: tsdown Exports Fix Across All Six Packages

Released as a coordinated patch, alpha.2 corrects a tsdown exports resolution regression that affected server, client, node, express, hono, and fastify packages simultaneously.
Upgrade all six packages together to avoid mismatched resolution at runtime.

MCP TypeScript SDK 2.0.0-alpha.1: Breaking Error Codes and WebSocket Transport Removal

Alpha.1 is a major release that aligns error handling with the MCP spec: unknown or disabled tool calls now reject with JSON-RPC code -32602 (InvalidParams) rather than returning a CallToolResult with isError set to true.
The WebSocketClientTransport has been removed entirely; callers must migrate to stdio or Streamable HTTP.

MCP TypeScript SDK 2.0.0-alpha.1: Fastify Middleware Adapter Added

The alpha.1 cycle introduces a first-class Fastify adapter for MCP servers, following the same pattern already established by the Express and Hono adapters.
Teams running Fastify-based backends can now integrate MCP without a custom transport wrapper.

MCP TypeScript SDK 2.0.0-alpha.1: WebSocket Client Transport Dropped from Client Package

The client alpha removes WebSocketClientTransport because WebSocket is not a spec-defined transport in MCP.
The Transport interface remains exported for custom implementations, so teams can build their own transport if needed.

MCP TypeScript SDK v1.29.0: Typings Exports, Null TTL Disallowed, ResourceSchema Size Field

The stable 1.x track receives a batch of fixes: infinite (null) requested TTL values are now rejected, a missing size field is added to ResourceSchema, and typings exports are wired up correctly.
The v1.x branch is also re-established as the target for the npm latest tag.

MCP TypeScript SDK v1.28.0: OAuth Scope Discovery and Plain JSON Schema Rejection

v1.28.0 defaults to reading scopes_supported from resource metadata for OAuth flows and falls back to client_secret_basic when the server omits token_endpoint_auth_methods_supported.
A separate fix rejects plain JSON Schema objects passed as inputSchema, catching a common authoring mistake.

MCP TypeScript SDK 2.0.0-alpha.1: Hono Adapter Switches to pnpm, Fixes Peer Dependencies

The hono and node alpha packages clean up package manager references (all pnpm now) and add the missing hono peer dependency that was previously only declared at the workspace root.
This resolves silent runtime resolution failures when consuming the node adapter in isolated projects.

Action Items

Immediate

Audit all tool-call error handling: replace result.isError checks for unknown tools with try/catch on rejected promises and handle JSON-RPC code -32602 (applies to any project targeting the 2.x alpha series).
Remove any usage of WebSocketClientTransport from client code and migrate to stdio or Streamable HTTP transport before adopting the 2.0.0-alpha packages.
If upgrading to 2.0.0-alpha.2, update all six packages together (server, client, node, express, hono, fastify) to avoid the tsdown exports resolution mismatch.
For Fastify-based MCP servers, evaluate the new @modelcontextprotocol/fastify 2.0.0-alpha adapter as a drop-in replacement for any custom transport wrapper.
On the stable 1.x track, upgrade to v1.29.0 to pick up the null TTL rejection, ResourceSchema size field fix, and corrected npm latest tag behavior.
Check that inputSchema definitions do not pass plain JSON Schema objects; v1.28.0 now rejects them, so validate your tool schemas before deploying.

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