mcp-omnienv-nix

MCP server that spins up Nix-backed, polyglot ephemeral environments. It uses nix shell to build disposable toolchains for interpreted stacks (Python, Node.js, Ruby, R, Lua; extendable) and runs your command inside that shell. Package availability depends on nixpkgs (e.g., python313Packages.requests, rPackages.misty, nodePackages.sloc).

Why

• Coding agents often need ad-hoc Python/Node/Ruby/R/Lua deps. Preloading everything is noisy; venvs clutter a system.
• With Nix on the host, this server asks for packages on demand, pulls them into the store, and leaves the rest of the environment clean—no venvs or global installs.
• Runs over MCP (stdio transport) so agent clients can call the tools directly.

Tools

• list_languages — enumerate supported languages and their base Nix packages.
• run_in_env(language, command, extra_packages?, timeout_seconds?) — launch a nix shell with base + extras and execute command. Returns JSON: stdout, stderr, exit_code.

Quick start

# Try it ad-hoc
nix shell github:StealthBadger747/mcp-omnienv-nix -c mcp-omnienv-nix

Hook into your MCP client (stdio transport). Example config shape:

{
  "mcpServers": {
    "mcp-omnienv-nix": {
      "command": "mcp-omnienv-nix"
    }
  }
}

Extending languages

• Edit SUPPORTED_LANGUAGES in mcp_omnienv_nix/server.py to add a language and its base packages.
• run_in_env validates extra packages against a simple regex and appends them to the nix shell invocation.

Development

# Nix dev shell with deps + pytest
nix develop . -c pytest
# Run integration tests (hit nix shell for real package resolution)
MCP_OMNIENV_INTEGRATION=1 nix develop . -c pytest -m integration

License

MIT.