Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add fredrikaverpil/dotfiles --skill nix-installgit clone --depth 1 https://github.com/fredrikaverpil/dotfilesWrote 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/fredrikaverpil/dotfiles/nix-install)<a href="https://agentmods.dev/skills/fredrikaverpil/dotfiles/nix-install"><img src="https://agentmods.dev/badge/skills/fredrikaverpil/dotfiles/nix-install/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/fredrikaverpil/dotfiles/nix-install"><img src="https://agentmods.dev/badge/skills/fredrikaverpil/dotfiles/nix-install.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00117 | $0.01111 |
| Opus 5.5 | $0.00047 | $0.00444 |
| Sonnet 5.5 | $0.00023 | $0.00222 |
| Haiku 4.5 | $0.00012 | $0.00111 |
Grade A, and why
nix-install scanned grade A with 1 finding 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 1mo 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.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
curl -sSI -o /dev/null -w "cache: %{http_code}\n" https://cache.nixos.org How it starts
The opening of the file, as written. The whole thing — 97 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Install Nix in the web sandbox
Nix is the most general way to install tools in the Claude Code web sandbox. The sandbox network is locked to package registries plus this session's GitHub repos, but two facts make Nix work anyway:
aptreaches the main Ubuntu archive, andnix-binis in it.cache.nixos.organdchannels.nixos.orgare reachable through the proxy, so Nix substitutes prebuilt binaries and pulls the nixpkgs expression without any GitHub access.
Scope: web sandbox only (CLAUDE_CODE_REMOTE=true). On a real machine Nix
is already the system package manager — do not run this there.
Step 0 — Verify the network path (usually already open)
curl -sSI -o /dev/null -w "cache: %{http_code}\n" https://cache.nixos.org
curl -sSI -o /dev/null -w "channels: %{http_code}\n" https://channels.nixos.org/nixpkgs-unstable/nixexprs.tar.xz
200/302 on both → proceed. If either is blocked, the environment's network
policy is stricter than default; widen it (claude.ai environment editor →
network / allowed hosts) to include cache.nixos.org and channels.nixos.org.
Step 1 — Install Nix (via apt)
Refresh the apt index, then install nix-bin:
apt-get update
apt-get install -y --no-install-recommends nix-bin
# Single-user (rootless-build) mode: the sandbox has no 'nixbld' build-users
# group, so disable multi-user builds or nix-env operations fail.
mkdir -p /etc/nix
grep -q '^build-users-group' /etc/nix/nix.conf 2>/dev/null \
|| echo 'build-users-group =' >> /etc/nix/nix.conf
nix --version
Step 2 — Install packages
Use classic nix-env against the channel tarball. Do not use flakes / nix run nixpkgs#pkg here: the nixpkgs flake reference resolves to
github.com/NixOS/nixpkgs, which the proxy blocks. The channel tarball is served
from the reachable channels.nixos.org, so this needs no GitHub:
TARBALL=https://channels.nixos.org/nixpkgs-unstable/nixexprs.tar.xz
nix-env -f "$TARBALL" -iA ripgrep # attribute name = nixpkgs attr path
export PATH="$HOME/.nix-profile/bin:$PATH"
rg --version
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.
- 1mo ago First seen · 97 lines · 117 tokens per session scan A 51e497eb1161
nix-install is a skill published in the GitHub repository fredrikaverpil/dotfiles (259 stars, last pushed yesterday), licensed MIT. It adds 117 tokens to every session and 1,111 once invoked, about $0.0005 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other skills, from other repositories
writing-skills
Use when creating new skills, editing existing skills, or verifying skills work before deployment.
executing-plans
Use when executing an implementation plan in the current session as the implementer yourself — your human partner chose inline execution, or no subagent tool is available.
brainstorming
You MUST use this before any creative work - creating features, building components, adding functionality, or modifying behavior. Explores user intent, requirements and design before implementation.
userscripts
Use when writing Tampermonkey/Violentmonkey/Greasemonkey userscripts, modifying website behavior or appearance, or working with .user.js files.
writing-plans
Use when you have a spec or requirements for a multi-step task, before touching code.
finishing-a-development-branch
Use when implementation is complete, all tests pass, and you need to decide how to integrate the work.