mcp-golang mcp server generates schema error

[ullgren]

Trying to implement a mcp server (STDIO) using mcp-golang. It works in other LLM clients however in gemini-cli it gives a schema error.

I can reproduce it using this simple mcp server, is this a bug in gemini-cli ?
Using gemini-cli v0.13.0-nightly.20251029.cca41edc with Node.js v25.1.0

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│ x  zipcode (zipcode-mcp-server MCP Server) {"zip_code":"88034102"}                                              │
│                                                                                                                 │
│    no schema with key or ref "https://json-schema.org/draft/2020-12/schema"                                     │
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