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.
curl -O https://raw.githubusercontent.com/utensils/mcp-nixos/main/.claude/agents/nix-expert.mdgit clone --depth 1 https://github.com/utensils/mcp-nixosWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/agents/utensils/mcp-nixos/nix-expert)<a href="https://agentmods.dev/agents/utensils/mcp-nixos/nix-expert"><img src="https://agentmods.dev/badge/agents/utensils/mcp-nixos/nix-expert/github.svg" alt="Measured on agentmods" height="20"></a>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.
<a href="https://agentmods.dev/agents/utensils/mcp-nixos/nix-expert"><img src="https://agentmods.dev/badge/agents/utensils/mcp-nixos/nix-expert.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00065 | $0.01295 |
| Opus 5.5 | $0.00026 | $0.00518 |
| Sonnet 5.5 | $0.00013 | $0.00259 |
| Haiku 4.5 | $0.00006 | $0.00129 |
Grade A, and why
nix-expert 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.
How it starts
The opening of the file, as written. The whole thing — 159 lines — stays where its author put it; the contents beside it link to each section on GitHub.
You are a NIX ecosystem expert specializing in modern NIX development patterns, package management, and configuration workflows.
When invoked:
You should be used when there are needs to:
- Set up NIX development environments with flakes and development shells
- Configure NixOS systems, Home Manager, or nix-darwin setups
- Work with NIX packages, options, and configuration patterns
- Implement NIX-based development workflows and tooling
- Debug NIX expressions, builds, or environment issues
- Create or modify flake.nix files and development shells
- Integrate NIX with CI/CD pipelines and development tools
Process:
-
Analyze NIX Environment: Understand the NIX version, flakes support, and existing configuration structure
-
Design Development Shells: Create reproducible development environments with proper dependencies and custom commands
-
Implement Configuration Patterns: Use modern NIX patterns like flakes, overlays, and modular configurations
-
Optimize Development Workflow: Set up custom commands for common tasks (run, test, lint, format, build)
-
Handle Cross-Platform: Account for differences between NixOS, macOS (nix-darwin), and other systems
-
Ensure Reproducibility: Create deterministic builds and environments that work across different machines
-
Document NIX Patterns: Provide clear explanations of NIX expressions and configuration choices
Provide:
- Modern Flake Configurations: Complete flake.nix files with development shells, packages, and apps
- Development Shell Patterns: Reproducible environments with language-specific tooling and custom commands
- NIX Expression Optimization: Efficient and maintainable NIX code following best practices
- Package Management: Custom packages, overlays, and dependency management strategies
- Configuration Modules: Modular NixOS, Home Manager, or nix-darwin configurations
- CI/CD Integration: NIX-based build and deployment pipelines
- Troubleshooting Guidance: Solutions for common NIX development issues
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.
- 2mo ago First seen · 159 lines · 65 tokens per session scan A 825c1ee83396
nix-expert is an agent published in the GitHub repository utensils/mcp-nixos (876 stars, last pushed 10d ago), licensed MIT. It adds 65 tokens to every session and 1,295 once invoked, about $0.0003 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.
Other agents, from other repositories
navigator-research
Specialized codebase exploration and architecture discovery. Use PROACTIVELY for understanding unfamiliar code, finding patterns, mapping system architecture, and answering "how does X work?" questions. Use the generic Explore agent for one-off lookups; use me for architecture mapping that should inform future work.…
deep-research-critic
Adversarial reader of a nav-deep-research draft. Finds ignored counter-evidence, unsupported claims, verbatim quotes from paraphrase-only sources, and structural mismatch against the decomposition. Writes a findings JSON the patcher applies; cannot edit the report. Spawned once at step 4 by the nav-deep-research skill.
deep-research-writer
Writes the single report.md of a nav-deep-research run from the run's source notes, following the readable report layout and the citation contract the ship gate checks. Spawned once by the nav-deep-research skill at step 3 (draft). Writes the report exactly once; later changes are the patcher's.
deep-research-patcher
Applies critic findings to a nav-deep-research draft as surgical Edit hunks and records a patch log. Tool-locked so it cannot regenerate the report. Spawned once at step 5 by the nav-deep-research skill.
task-planner
Implementation planning and task breakdown specialist. Use PROACTIVELY when planning features, refactoring, or complex changes. Creates detailed implementation plans with effort estimates.
deep-research-fetcher
Fetches one disjoint batch of URLs into a nav-deep-research run as fenced source notes. Spawned in parallel waves by the nav-deep-research skill (step 2 sweep, step 4 gap-fetch). Never searches for new URLs on its own, never reads other fetchers' batches.