Claude Code: MCP server connects but shows no tools (or every tool call fails)

The error

Why it happens

The MCP spec released on July 28, 2026 (protocol version 2026-07-28) changed the shape of server replies. Claude Code versions before 2.1.302 could show no tools, or fail every tool call, when a server negotiated that new version but left out the fields resultType, ttlMs or cacheScope. Claude Code 2.1.302 (released October 16, 2026) fixed this.

How to fix it

1. Check your Claude Code version
   If the number is below 2.1.302, you have the affected version.

   claude --version

2. Update Claude Code
   The native installer updates with claude update. If you installed with npm, reinstall the latest package instead.

   claude update
   # or, for npm installs:
   npm install -g @anthropic-ai/claude-code@latest

3. Restart and re-check
   Start a new Claude Code session and run /mcp to confirm the server now lists its tools.
4. If you build the server
   Make sure every result includes the fields the 2026-07-28 spec requires (for example resultType: "complete"), so older clients and other tools also work. See the spec changelog below.

Related servers

Sources

• https://github.com/anthropics/claude-code/blob/main/CHANGELOG.md
• https://modelcontextprotocol.io/specification/2026-07-28/changelog
• https://code.claude.com/docs/en/setup