ByteAid.b4.Roslyn 0.3.0

b4.Roslyn

MCP (Model Context Protocol) server that lets AI agents work with .NET solutions efficiently through Roslyn: persistent in-memory semantic models, solution pre-compilation, code navigation, safe refactoring, diagnostics, file edits, builds and test execution — everything you would do with an IDE, over stdio (IPC).

Built on the official ModelContextProtocol C# SDK and .NET 10.

Install

dotnet tool install -g ByteAid.b4.Roslyn

This installs the b4-roslyn command. Optionally install the ByteAid.b4 dispatcher for the unified family entry point (b4 roslyn start → b4-roslyn start):

dotnet tool install -g ByteAid.b4

Start

cd path/to/your/repo
b4-roslyn start          # or, with the dispatcher: b4 roslyn start

The server takes the current working directory as root and uses the single .sln/.slnx file found at that level as entry point. When there is more than one (or none), it fails asking for an explicit solution:

b4-roslyn start --solution MyApp.sln

The solution loads in the background at startup, and its semantic models stay alive in memory for the whole session — repeated queries are fast.

MCP client configuration

Claude Code:

claude mcp add b4-roslyn -- b4-roslyn start

Generic .mcp.json:

{
  "mcpServers": {
    "b4-roslyn": {
      "command": "b4-roslyn",
      "args": ["start"]
    }
  }
}

Tools

Edit-validate-save workflow

Edits (update_document, replace_in_document, apply_text_edits, rename_symbol, format_document, create_document) are applied to an in-memory overlay and immediately return the resulting compiler diagnostics, so an agent can validate a change before touching disk. save_changes persists everything; discard_changes reverts. build/run_tests run against disk state and warn when unsaved overlay changes exist.

Notes

• Logs go to stderr; stdout is reserved for the MCP stdio protocol.
• Requires the .NET 10 SDK (project loading uses the MSBuild build host of the installed SDK).