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.