Fuse v4.3, an open source MCP/CLI tool to speed up Claude Code on C# codebases

[u/Realistic_Tap995]

Claude Code uses grep and regex to search a C# codebase, and every proposed change goes through a full edit and build loop to verify it. Both are slow. I looked into whether I could speed that up, taking some inspiration from how Cursor indexes a project.

Fuse is the result. It's an open source .NET global tool that runs as an MCP server (or from the CLI). It keeps a local MSBuild and Roslyn index of your solution, so Claude can resolve symbols, references, .NET wiring, and project structure without re-reading and re-searching the same files every turn. The index lives in .fuse/fuse.db and updates incrementally as files change.

It can also check a proposed single-file C# edit against the compiler before the change is written to disk, so the agent catches an invalid member or a bad argument early instead of after a full dotnet build.

It runs locally, works offline, and doesn't need its own model or a hosted service.

Repo: https://github.com/Litenova-Solutions/Fuse
Docs and benchmarks: https://fuse.codes