Serena.DotNet

A code-aware MCP (Model Context Protocol) coding agent for C# / .NET, with Roslyn LSP integration. Targets .NET 10. Inspired by and indebted to oraios/serena.

Distributed as the global tool Serena.DotNet (executable serena-dotnet).

Status: 0.1.0 — public preview. API surface is stable enough for daily use; expect minor tool-schema tweaks before 1.0.

Origin

I built this because I wanted the symbol-aware MCP experience of oraios/serena without the Python/uv/uvx install dance on every dev machine. On Windows-heavy .NET shops, dotnet tool install -g is already the established way developers ship CLI tooling — one binary, one PATH entry, predictable updates, no per-project venv. This project is a from-scratch reimplementation of the agent-facing tool surface in .NET, optimized for C# codebases as the primary target. It is not a fork — no Python code was translated — but the tool naming, the symbol-aware approach, the project-activation model, and the memory system all come from oraios/serena's design.

Acknowledgements

oraios/serena by Oraios AI is the original. Their design — symbol-level tools, project-based workflow, memory system, language-server backend abstraction — is the foundation this project builds on. If you work in Python, Java, Rust, Go, TypeScript, or any of the 40+ languages they support, use theirs. They've put years of work into a polished, multi-language product. This project exists to serve a narrower audience — C# developers who already have the .NET SDK installed and want a single-binary install — and may be the right fit for that case.

Installation

dotnet tool install -g Serena.DotNet

Update an existing install:

dotnet tool update -g Serena.DotNet

No Python, no uv, no virtualenv. If you have the .NET 10 SDK, you already have everything you need.

How Serena.DotNet differs from oraios/serena

CLI

serena-dotnet serve                        # Start the MCP server over stdio
serena-dotnet config show                  # Print current config
serena-dotnet config init                  # Write default ~/.serena/config.yml
serena-dotnet register <name> <path>       # Register a project
serena-dotnet list-projects                # Show registered projects
serena-dotnet setup                        # Initialize .serena/ in current dir
serena-dotnet doctor                       # Check LSP prerequisites
serena-dotnet project index .              # Build the symbol cache for this repo
serena-dotnet version                      # Show version info

MCP Client Configuration

Minimal stdio entry for VS Code (.vscode/mcp.json) or any MCP client:

{
  "servers": {
    "serena-dotnet": {
      "type": "stdio",
      "command": "serena-dotnet",
      "args": ["serve"],
      "env": {
        "SERENA_TOOL_TIMEOUT_SECONDS": "600",
        "SERENA_LSP_REQUEST_TIMEOUT_SECONDS": "600",
        "SERENA_LSP_PARALLELISM": "2"
      }
    }
  }
}

The MCP client launches serena-dotnet serve with the workspace folder as its working directory, and Serena auto-activates whatever repo is at that path — so the same config works in every workspace, no per-repo edits. The env vars are optional but recommended for large solutions where Roslyn warmup or per-request work can exceed the lower defaults.

Tools (38)

Symbol-tool ergonomics (v1.0.34)

• find_symbol returns outline-first when include_body=true: a compact name-path/line-range index for every match precedes the bodies, so even when the MCP client spills the response to a sidecar file, the inline header still tells the agent where everything is. Bodies that exceed the per-body cap are replaced with a <body omitted: N chars; re-call ... include_body=true> hint that includes the exact arguments to fetch them.
• find_symbol with match_overloads: true returns every symbol whose leaf name matches the pattern's last segment, regardless of parent path — purpose-built for enumerating method overloads in a single call.
• When find_symbol finds no exact match, it auto-suggests symbols with the same leaf name as a "did you mean" list (using the cache it already loaded — no extra LSP calls).
• get_symbols_overview auto-descends past pure container kinds (Namespace, Module, Package). C# files almost always have a single wrapping namespace, so depth=0 now returns the actual class/method outline instead of the namespace span. Pass auto_descend_containers: false to opt out.

File-write behavior

All edit tools (replace_content, create_text_file, insert_at_line, replace_lines, delete_lines, and the symbol-edit tools) preserve the target file's existing UTF-8 BOM state. Files without a BOM stay BOM-free; files with one keep theirs. Newly created files are written without a BOM.

Performance on Large Repos

For repos with thousands of source files (e.g. monorepos with hundreds of projects), find_symbol is cache-first by default. Build the cache once per repo:

serena-dotnet project index .

After that, every find_symbol call:

1. Serves results from the on-disk symbol cache (no LSP traffic).
2. Runs a debounced parallel fingerprint check on cached files.
3. Auto-reindexes up to 10 stale files inline so subsequent calls stay fresh.

If more than 10 cached files have changed since the last index (e.g. after a git pull), the refresher logs a warning and skips inline reindex — re-run serena-dotnet project index . to refresh the bulk.

The cache lives under .serena/cache/<lang>/symbols.json in the repo and is fingerprinted by file size + LastWriteTimeUtc.

Tunable env vars

Building from source

dotnet build
dotnet test
dotnet pack -c Release src/Serena.Cli/Serena.Cli.csproj -o nupkg
dotnet tool update -g Serena.DotNet --add-source ./nupkg

See BUILD.md for additional notes.

License

MIT