# External (non-OpenAI) Pull Request Requirements Currently, mcp server fail to start with: ``` 🖐 MCP client for `<CLIENT>` failed to start: missing field `user_agent` ```` It isn't clear to me yet why this is happening. My understanding is that this struct is simply added as a new field to the response but this should fix it until I figure out the full story here. <img width="714" height="262" alt="CleanShot 2025-09-10 at 13 58 59" src="https://github.com/user-attachments/assets/946b1313-5c1c-43d3-8ae8-ecc3de3406fc" />
mcp-types
Types for Model Context Protocol. Inspired by https://crates.io/crates/lsp-types.
As documented on https://modelcontextprotocol.io/specification/2025-06-18/basic:
- TypeScript schema is the source of truth: https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/2025-06-18/schema.ts
- JSON schema is amenable to automated tooling: https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/2025-06-18/schema.json