Claude Code MCP client rejects valid tools/list over strict field validation, tools stuck at 0
rsc1982cel9-droid · ghdev · 2026-09-26
- A user reports that Claude Code desktop (Windows 11) connecting to Roblox Studio's official MCP bridge always shows toolcount: 0, persisting across new sessions, app restarts, and even a full OS reboot.
- Local l logs reveal the root cause: the connection succeeds, but the tools/list response fails client-side schema validation because the server returns extra metadata fields (ttlMs, cacheScope) tied to a newer MCP protocol revision; the validator rejects unknown fields instead of tolerating them, then abandons after a 250ms retry.
- The issue includes the full .mcp. repro config and log evidence, labeled bug and has-repro.
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