agentmods.dev

mcp-nixos: Instructions file for GitHub Copilot

.github/copilot-instructions.md

mcp-nixos copilot-instructions.md is an instructions file for GitHub Copilot from utensils/mcp-nixos. It costs 1,510 tokens per session, scanned A, original, MIT.

Development instructions for MCP-NixOS, a server that provides current information about NixOS packages and configuration through the Model Context Protocol, a way for AI tools to call data services.

In plain words
What is it for?
Use them to develop, run, test, lint, format, type-check, and build MCP-NixOS with its required Nix flake environment.
Why use it?
They describe the server’s modules and require the Nix development environment, helping agents use the project’s intended setup and checks.

Instructions file for GitHub Copilot

Written for GitHub Copilot: a Copilot instructions file. Also seen: mentions AGENTS.md.

This is utensils/mcp-nixos's own configuration. It tells GitHub Copilot how to work on mcp-nixos itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything mcp-nixos configures →

not rated 876repo +8 changed 2mo ago A scan 1,510 tokens original MIT
View source ↗ utensils/mcp-nixos mcp-nixos.io
Reuse

Borrowing it

Nothing to install: this file belongs to utensils/mcp-nixos. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/utensils/mcp-nixos/main/.github/copilot-instructions.md
Clone the repo
git clone --depth 1 https://github.com/utensils/mcp-nixos

Made for: GitHub Copilot.

Wrote this? Show the measurements

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README.md
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Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

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<a href="https://agentmods.dev/instructions/utensils/mcp-nixos/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/utensils/mcp-nixos/copilot-instructions.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 1,510 This file is loaded in full into every session.
When invoked 1,510 The same file — it is already loaded in full.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.01510 $0.01510
Opus 5.5 $0.00604 $0.00604
Sonnet 5.5 $0.00302 $0.00302
Haiku 4.5 $0.00151 $0.00151

Measured 2mo ago against content hash 14155362f8b0, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

mcp-nixos copilot-instructions.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/copilot-instructions.md · 128 lines

How it starts

The opening of the file, as written. The whole thing — 128 lines — stays where its author put it; the contents beside it link to each section on GitHub.

GitHub Copilot Instructions for MCP-NixOS

Project Context

MCP-NixOS is a Model Context Protocol (MCP) server providing real-time information about NixOS packages, options, Home Manager, nix-darwin, and flakes. The server prevents AI hallucination by querying official APIs and documentation sources.

Architecture: Modular FastMCP 4.x async server exposing only 2 MCP tools (consolidated from 17 in v1.0 to reduce context window usage).

Key Modules:

  • mcp_nixos/server.py - MCP tools, routing, and entry point
  • mcp_nixos/sources/ - Per-source modules (nixos, home_manager, darwin, flakehub, wiki, etc.)
  • mcp_nixos/config.py - Configuration constants
  • mcp_nixos/caches.py - Cache implementations
  • mcp_nixos/utils.py - Shared utilities

Core Development Workflows

Build & Test Commands (Nix Flake Required)

nix develop              # Enter dev shell with Python venv
run                      # Start MCP server
run-tests               # Run all tests with coverage
lint                    # Check code with ruff
format                  # Format code with ruff
typecheck               # Run mypy type checker
build                   # Build package distributions

Python-only alternative: uv pip install -e ".[dev]" then uv run mcp-nixos

Testing Strategy

  • Markers: @pytest.mark.unit or @pytest.mark.integration (defined in tests/conftest.py)
  • Integration tests hit real APIs - no mocks, use @pytest.mark.flaky(reruns=3) for flaky network calls
  • Async everywhere: pytest-asyncio auto mode enabled, function-scoped event loops
  • Coverage: Always enabled (--cov=mcp_nixos)
  • Output validation: All tests verify plain text output (no XML/JSON leakage)

Run specific tests: pytest tests/test_server.py::test_nixos_search -v

Project-Specific Patterns

1. Plain Text Output Only

Critical: All MCP tool responses must return plain text formatted for LLM consumption. Never return raw JSON or XML to users.

Read the full file on GitHub · 128 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2mo ago Changed 14155362f8b0
  2. 2mo ago First seen · 128 lines · 1,510 tokens per session scan A 83e063cf698c

Subscribe to this mod's changes

mcp-nixos copilot-instructions.md is an instructions file published in the GitHub repository utensils/mcp-nixos (876 stars, last pushed 10d ago), licensed MIT. It adds 1,510 tokens to every session, about $0.0060 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

ai-assistantai-integrationai-toolsanthropicclaudedeveloper-tools
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