Mcp Nixos

What is Mcp Nixos about?

Mcp Nixos delivers accurate, up‑to‑date information about the NixOS ecosystem—including over 130 000 packages, 22 000 configuration options, Home Manager settings, and macOS (nix‑darwin) options—through an MCP server. AI assistants can query this server to obtain concrete package details, version histories, and configuration suggestions without needing a local Nix/NixOS installation.

How to use Mcp Nixos?

Run the server using one of the supported methods:
- uvx (recommended) – uvx mcp-nixos
- pip – pip install mcp-nixos && mcp-nixos
- Nix – nix run github:utensils/mcp-nixos
- Docker – docker run --rm -i ghcr.io/utensils/mcp-nixos
Configure your AI client (e.g., Claude Code) with a .mcp.json pointing to the local server.
Call the provided MCP methods such as nixos_search, nixos_info, home_manager_search, or nixhub_package_versions to retrieve data.

Key features of Mcp Nixos

Async FastMCP 2.x for low‑latency, non‑blocking queries.
Stateless operation – no local caches or temporary files.
Comprehensive data sets:
- Packages (130 K+)
- NixOS options (22 K+)
- Home Manager options (4 K+)
- nix‑darwin macOS options (1 K+)
- Version history via NixHub.io.
Cross‑platform – works on Windows, macOS, and Linux.
Smart suggestions for misspelled option names.
Dynamic channel resolution – stable always points to the current stable channel.

Use cases of Mcp Nixos

AI‑assisted development: Let large language models suggest exact package names or configuration flags while writing Nix expressions.
Automated CI checks: Verify that a referenced package or option exists before committing.
Documentation generation: Pull live option descriptions to keep docs in sync with upstream NixOS.
Version audit: Retrieve historical package versions and commit hashes for security reviews.
Cross‑environment tooling: Provide consistent Nix data to both Linux and macOS developers.

FAQ from the Mcp Nixos

Do I need Nix/NixOS installed? No. The server queries public APIs and runs on any system with Python.
Which installation method is best? For most users, uvx mcp-nixos requires no setup. Pip works if you prefer a traditional installation.
How do I change the NixOS channel? Use the nixos_channels() method to list available channels and pass the desired channel name to other functions.
Can I query private package indexes? The server only accesses public endpoints (search.nixos.org and NixHub.io). Private indexes would require a custom implementation.
What environment variables are required? Only ELASTICSEARCH_URL can be overridden; it defaults to https://search.nixos.org/backend.
Why is everything async now? Async I/O improves responsiveness when multiple AI queries are in flight.
I get a sandbox error on Nix? Run with --option sandbox relaxed or set sandbox = relaxed in /etc/nix/nix.conf.

MCP-NixOS - Because Your AI Assistant Shouldn't Hallucinate About Packages

🎉 REFACTORED: Version 1.0.0 represents a complete rewrite that drastically simplified everything. We removed all the complex caching, abstractions, and "enterprise" patterns. Because sometimes less is more, and more is just showing off.

🚀 ASYNC UPDATE: Version 1.0.1 migrated to FastMCP 2.x for modern async goodness. Because who doesn't love adding await to everything?

Quick Start (Because You Want to Use It NOW)

🚨 No Nix/NixOS Required! This tool works on any system - Windows, macOS, Linux. You're just querying web APIs.

Option 1: Using uvx (Recommended for most users)

{
  "mcpServers": {
    "nixos": {
      "command": "uvx",
      "args": ["mcp-nixos"]
    }
  }
}

Option 2: Using Nix (For Nix users)

{
  "mcpServers": {
    "nixos": {
      "command": "nix",
      "args": ["run", "github:utensils/mcp-nixos", "--"]
    }
  }
}

Option 3: Using Docker (Container lovers unite)

{
  "mcpServers": {
    "nixos": {
      "command": "docker",
      "args": ["run", "--rm", "-i", "ghcr.io/utensils/mcp-nixos"]
    }
  }
}

That's it. Your AI assistant now has access to real NixOS data instead of making things up. You're welcome.

What Is This Thing?

MCP-NixOS is a Model Context Protocol server that gives your AI assistant accurate, real-time information about:

NixOS packages (130K+ packages that actually exist)
Configuration options (22K+ ways to break your system)
Home Manager settings (4K+ options for the power users)
nix-darwin configurations (1K+ macOS settings Apple doesn't want you to touch)
Package version history via NixHub.io (Find that ancient Ruby 2.6 with commit hashes)

The Tools You Actually Care About

🔍 NixOS Tools

nixos_search(query, type, channel) - Search packages, options, or programs
nixos_info(name, type, channel) - Get detailed info about packages/options
nixos_stats(channel) - Package and option counts
nixos_channels() - List all available channels
nixos_flakes_search(query) - Search community flakes
nixos_flakes_stats() - Flake ecosystem statistics

📦 Version History Tools (NEW!)

nixhub_package_versions(package, limit) - Get version history with commit hashes
nixhub_find_version(package, version) - Smart search for specific versions

🏠 Home Manager Tools

home_manager_search(query) - Search user config options
home_manager_info(name) - Get option details (with suggestions!)
home_manager_stats() - See what's available
home_manager_list_options() - Browse all 131 categories
home_manager_options_by_prefix(prefix) - Explore options by prefix

🍎 Darwin Tools

darwin_search(query) - Search macOS options
darwin_info(name) - Get option details
darwin_stats() - macOS configuration statistics
darwin_list_options() - Browse all 21 categories
darwin_options_by_prefix(prefix) - Explore macOS options

Installation Options

Remember: You DON'T need Nix/NixOS installed! This tool runs anywhere Python runs.

For Regular Humans (Windows/Mac/Linux)

# Run directly with uvx (no installation needed)
uvx mcp-nixos

# Or install globally
pip install mcp-nixos
uv pip install mcp-nixos

For Nix Users (You Know Who You Are)

# Run without installing
nix run github:utensils/mcp-nixos

# Install to profile
nix profile install github:utensils/mcp-nixos

Features Worth Mentioning

🚀 Version 1.0.1: The Async Revolution (After The Great Simplification)

Drastically less code - v1.0.0 removed thousands of lines, v1.0.1 made them async
100% functionality - Everything still works, now with more await
0% cache corruption - Because we removed the cache entirely (still gone!)
Stateless operation - No files to clean up (async doesn't change this)
Direct API access - No abstraction nonsense (but now it's async nonsense)
Modern MCP - FastMCP 2.x because the old MCP was too synchronous

📊 What You Get

Real-time data - Always current, never stale
Plain text output - Human and AI readable
Smart suggestions - Helps when you typo option names
Cross-platform - Works on Linux, macOS, and yes, even Windows
No configuration - It just works™

🎯 Key Improvements

Dynamic channel resolution - stable always points to current stable
Enhanced error messages - Actually helpful when things go wrong
Deduped flake results - No more duplicate spam
Version-aware searches - Find that old Ruby version you need
Category browsing - Explore options systematically

For Developers (The Brave Ones)

Local Development Setup

Want to test your changes in Claude Code or another MCP client? Create a .mcp.json file in your project directory:

{
  "mcpServers": {
    "nixos": {
      "type": "stdio",
      "command": "uv",
      "args": [
        "run",
        "--directory",
        "/home/hackerman/Projects/mcp-nixos",
        "mcp-nixos"
      ]
    }
  }
}

Replace /home/hackerman/Projects/mcp-nixos with your actual project path (yes, even you, Windows users with your C:\Users\CoolDev\... paths).

This .mcp.json file:

Automatically activates when you launch Claude Code from the project directory
Uses your local code instead of the installed package
Enables real-time testing - just restart Claude Code after changes
Already in .gitignore so you won't accidentally commit your path

With Nix (The Blessed Path)

nix develop
menu  # Shows all available commands

# Common tasks
run        # Start the server (now with FastMCP!)
run-tests  # Run all tests (now async!)
lint       # Format and check code (ruff replaced black/flake8)
typecheck  # Check types (mypy still judges you)
build      # Build the package
publish    # Upload to PyPI (requires credentials)

Without Nix (The Path of Pain)

# Install development dependencies
uv pip install -e ".[dev]"  # or pip install -e ".[dev]"

# Run the server locally
uv run mcp-nixos  # or python -m mcp_nixos.server

# Development commands
pytest tests/          # Now with asyncio goodness
ruff format mcp_nixos/ # black is so 2023
ruff check mcp_nixos/  # flake8 is for boomers
mypy mcp_nixos/        # Still pedantic as ever

# Build and publish
python -m build        # Build distributions
twine upload dist/*    # Upload to PyPI

Testing Philosophy

367 tests that actually test things (now async because why not)
Real API calls because mocks are for cowards (await real_courage())
Plain text validation ensuring no XML leaks through
Cross-platform tests because Windows users deserve pain too
15 test files down from 29 because organization is a virtue

Environment Variables

Just one. We're minimalists now:

Variable	Description	Default
`ELASTICSEARCH_URL`	NixOS API endpoint	https://search.nixos.org/backend

Troubleshooting

Nix Sandbox Error

If you encounter this error when running via Nix:

error: derivation '/nix/store/...-python3.11-watchfiles-1.0.4.drv' specifies a sandbox profile, 
but this is only allowed when 'sandbox' is 'relaxed'

Solution: Run with relaxed sandbox mode:

nix run --option sandbox relaxed github:utensils/mcp-nixos --

Why this happens: The watchfiles package (a transitive dependency via MCP) requires custom sandbox permissions for file system monitoring. This is only allowed when Nix's sandbox is in 'relaxed' mode instead of the default 'strict' mode.

Permanent fix: Add to your /etc/nix/nix.conf:

sandbox = relaxed

Acknowledgments

This project queries data from several amazing services:

NixHub.io - Provides package version history and commit tracking
search.nixos.org - Official NixOS package and option search
Jetify - Creators of Devbox and NixHub

Note: These services have not endorsed this tool. We're just grateful API consumers.

License

MIT - Because sharing is caring, even if the code hurts.

Created by James Brink and maintained by masochists who enjoy Nix and async/await patterns.

Special thanks to the NixOS project for creating an OS that's simultaneously the best and worst thing ever.

Mcp Nixos Overview