I have been converting OpenAPI documents into function calling schemas and doing tool calling since function calling first came out in 2023, but it's not easy to recreate a backend server to fit MCP.
Also, these days, I'm making a compiler-driven function calling specialized framework, but I'm a little cautious about whether MCP will support it. It enables zero-cost tool calling for TypeScript classes based on the compiler, and it also supports OpenAPI.
However, in the case of MCP, in order to fit this to the compiler-driven philosophy, I need to create a backend framework for MCP development first, or create an add-on library for a famous framework like NestJS. I can do the development, but there's so much more to do compared to OpenAPI tool calling, so it's a bit like that.