Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/rikdc/ai-skillsnpx agentmods add skills/rikdc/ai-skills/nix-expertWrote 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/skills/rikdc/ai-skills/nix-expert)<a href="https://agentmods.dev/skills/rikdc/ai-skills/nix-expert"><img src="https://agentmods.dev/badge/skills/rikdc/ai-skills/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/skills/rikdc/ai-skills/nix-expert"><img src="https://agentmods.dev/badge/skills/rikdc/ai-skills/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 | $0.00169 | $0.03713 |
| Opus 5 | $0.00084 | $0.01857 |
| Sonnet 5 | $0.00034 | $0.00743 |
| Haiku 4.5 | $0.00017 | $0.00371 |
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 12d 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 — 501 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Nix Expert
Advisory guidance on Nix, NixOS, and home-manager. This skill answers questions, explains patterns, and reviews Nix code.
Scope
Use this skill for:
- Explaining or reviewing Nix expressions and module definitions
- Authoring derivations and overlays
- Flake input management and lockfile hygiene
- Debugging build and evaluation failures
- home-manager configuration
- Secrets management patterns
- NixOS security hardening
When the task is to author or change .nix files for a specific host, check
whether the target repository ships its own config-generation skill and prefer
it — it will know that flake's layout, secrets backend, and conventions, which
this skill deliberately does not assume. Failing that, read the existing tree
before writing anything, and conform to what is already there.
Routing
Read the matching reference file rather than answering from this file when the request is specific. Each one is a task-oriented procedure, not passive background:
| Topic | Trigger | Reference |
|---|---|---|
| Build | "build nix package", "nixos-rebuild build", "compile nix" | references/Build.md |
| Debug | "debug nix", "nix error", "evaluation error", "infinite recursion" | references/Debug.md |
| Develop | "development shell", "nix develop", "devShell", "direnv" | references/Develop.md |
| Deploy | "deploy nixos", "nixos-rebuild switch", "remote deployment" | references/Deploy.md |
| Package | "create package", "derivation", "buildGoModule", "package app" | references/Package.md |
| Flakes | "create flake", "flake.lock", "update inputs", "flake outputs" | references/Flakes.md |
| Secrets | "manage secrets", "agenix", "encrypt secrets", "age encryption" | references/Secrets.md |
| Security | "harden nixos", "apparmor", "firewall", "security hardening" | references/Security.md |
| Troubleshoot | "hash mismatch", "nix failing", "common errors" | references/Troubleshoot.md |
What ships with it
9 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 12d ago First seen · 501 lines · 169 tokens per session scan A 311ff483e07e
nix-expert is a skill published in the GitHub repository rikdc/ai-skills (2 stars, last pushed 6d ago), licensed MPL-2.0. It adds 169 tokens to every session and 3,713 once invoked, about $0.0008 per session on Opus 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 2026-08-31.
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