Wollmilchsau

License: MIT Platforms: Windows, macOS, Linux

Stop making the LLM think — give it a V8 sandbox and let it write code.

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// Features

Why choose Wollmilchsau.

V8-Powered Performance

Embeds the V8 JavaScript engine directly via CGO — near-native TypeScript execution in the same memory space.

Secure Sandbox

No network, no filesystem, no Node.js APIs. Scripts run fully isolated with configurable timeouts.

Instant TypeScript

In-process esbuild compiles and bundles TypeScript on the fly — no pre-build steps, no subprocess.

Source Maps

Errors point to the exact TypeScript line. The agent can read, fix, and retry automatically.

Artifact Integration

Large outputs are automatically saved via openArtifact() — keeping tool responses lean.

stdio + SSE Transport

Works locally with Claude Desktop (stdio) and remotely over SSE — one binary, both modes.

// The LLM Writes Code — Wollmilchsau Runs It

The LLM Writes Code — Wollmilchsau Runs It

Instead of reasoning through data transformations step by step, the agent writes a small TypeScript program. Wollmilchsau runs it in an isolated V8 sandbox and returns a deterministic result in milliseconds.

Self-correcting: errors with source maps are fed back to the agent
In-process esbuild — no subprocess overhead
Structured JSON output for reliable tool parsing

The LLM Writes Code — Wollmilchsau Runs It

Wollmilchsau is a high-performance TypeScript execution engine designed specifically for Model Context Protocol (MCP) servers.

What it does

Executing TypeScript logic within an MCP server usually requires a full Node.js or Deno runtime, which adds significant overhead and complexity. Wollmilchsau solves this by embedding the powerful V8 JavaScript engine directly into a Go binary. This allows it to run TypeScript tools with near-native performance, zero external dependencies, and a minimal memory footprint.

Key features

V8 Engine Performance: By using the same engine that powers Chrome and Node.js, Wollmilchsau ensures your MCP tools run as fast as possible.
Embedded esbuild: Automatically bundles and transpiles your TypeScript files on the fly, so you don't need a complex build pipeline.
Seamless Go Integration: Designed to be the scriptable heart of Go-based MCP servers, allowing you to define tool logic in TypeScript while maintaining the robustness of Go for the server transport.
Artifact Support: Built-in connection to the mlcartifact service, allowing your scripts to produce and manage persistent results easily.

Quick Setup

Claude Desktop

Add the following to your claude_desktop_config.json:

{
  "mcpServers": {
    "wollmilchsau": {
      "command": "wollmilchsau",
      "args": ["-enable-artifacts"]
    }
  }
}

Gemini-CLI

Add to your ~/.gemini/settings.json:

{
  "mcpServers": {
    "wollmilchsau": {
      "command": "wollmilchsau",
      "args": ["-enable-artifacts"]
    }
  }
}

MCP-Tester

Add a new profile:

mcp-tester profile add wollmilchsau -c "wollmilchsau --enable-artifacts"