Using ui-mcp-proxy in Llama-cpp

A developer created a simple MCP server for local LLMs to call Rust-coded tools, but encountered CORS errors. The llama-cpp feature ui-mcp-proxy, passed as an argument to llama-server, sets up a proxy that eliminates CORS errors by placing the MCP server on the same server as llama-cpp, simplifying code by removing CORS middleware.

Yesterday I developed a simple MCP server , which allows local LLMs to call tools that I have written in Rust code. This worked well, but I ran into CORS errors —CORS is a security feature on web browsers. I found that llama-cpp has a special feature to avoid these issues. With ui-mcp-proxy , passed as an argument to llama-server , a proxy server is set up so that the MCP server is on the same server as llama-cpp . This eliminates the CORS errors altogether. I was able to remove the middleware logic that set up CORS headers—it wasn't a huge win, but anything that simplifies code is a benefit . After all, code is a burden and having the minimal amount of necessary code will make life easier. According to the Model Context Protocol specification, JSON-encoded messages must be used, so there will always be some complexity due to decoding and encoding messages. That is essential complexity here.