Agent skill

Nix Debug

Deep debugging of Nix expressions, evaluation, and derivations

No licenceAuto-check: notesDevelopment

Install Nix Debug

skills CLI

$ npx skills add r17x/universe --skill nix-debug -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install r17x/universe nix-debug --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/r17x/universe.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.claude/skills/nix/debug .claude/skills/nix-debug && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "nix-debug" agent skill from https://github.com/r17x/universe/tree/main/.claude/skills/nix/debug into .claude/skills/nix-debug/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "nix-debug", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/r17x/universe/tree/main/.claude/skills/nix/debug

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add r17x/universe --skill nix-debug -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install r17x/universe nix-debug --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/r17x/universe.git skills-src && mkdir -p .agents/skills && cp -r skills-src/.claude/skills/nix/debug .agents/skills/nix-debug && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "nix-debug" agent skill from https://github.com/r17x/universe/tree/main/.claude/skills/nix/debug into .agents/skills/nix-debug/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "nix-debug", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add r17x/universe --skill nix-debug -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install r17x/universe nix-debug --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/r17x/universe.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/.claude/skills/nix/debug .cursor/skills/nix-debug && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "nix-debug" agent skill from https://github.com/r17x/universe/tree/main/.claude/skills/nix/debug into .cursor/skills/nix-debug/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "nix-debug", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/r17x/universe.git --path .claude/skills/nix/debug

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add r17x/universe --skill nix-debug -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install r17x/universe nix-debug --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/r17x/universe.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/.claude/skills/nix/debug .gemini/skills/nix-debug && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "nix-debug" agent skill from https://github.com/r17x/universe/tree/main/.claude/skills/nix/debug into .gemini/skills/nix-debug/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "nix-debug", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install r17x/universe nix-debug

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add r17x/universe --skill nix-debug -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/r17x/universe.git skills-src && mkdir -p .github/skills && cp -r skills-src/.claude/skills/nix/debug .github/skills/nix-debug && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "nix-debug" agent skill from https://github.com/r17x/universe/tree/main/.claude/skills/nix/debug into .github/skills/nix-debug/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "nix-debug", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add r17x/universe --skill nix-debug -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install r17x/universe nix-debug --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/r17x/universe.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/.claude/skills/nix/debug .opencode/skills/nix-debug && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "nix-debug" agent skill from https://github.com/r17x/universe/tree/main/.claude/skills/nix/debug into .opencode/skills/nix-debug/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "nix-debug", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: nix-debug
GitHub stars: 151
Token cost: ~1.6k tokens
SKILL.md length: 69 words
Files: 1
Skills in repo: 5
Repo updated: Oct 4, 2026
First seen: Oct 7, 2026
Licence: None found

At a glance

Deep debugging of Nix expressions, evaluation, and derivations

Tasks that involve Debugging
SKILL.md covers nix eval - Complete Reference, nix repl - Interactive Debugging, Built-in Debug Functions and Interactive Debugger (Nix 2.9+), plus 6 more sections
Calls nix and jq

What it does

Nix Debug is an agent skill from r17x/universe. Deep debugging of Nix expressions, evaluation, and derivations

Its SKILL.md is about 1.6k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Development, covering Debugging. The repository describes itself as: let universe speak itself ❄️ ƛ.

When your agent uses it

Tasks that involve Debugging

Example prompts

“/nix-debug”

Requirements

Pre-approved tools (allowed-tools): Bash, Read

What it can do on your machine

Read from SKILL.md and the folder at commit 489dbda. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves these tools, so the agent can use them without asking each time:
- Bash
- Read
From allowed-tools in the SKILL.md frontmatter.
Runs code
Shell commands in SKILL.md call:
- nix
- jq
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Nix Debug loads about 1.6k tokens when it runs. Until then it costs about 18 tokens; SKILL.md has 69 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~18
When it runs · the whole SKILL.md, loaded when a task matches: ~1.6k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check: notes

The automated check noted patterns worth knowing about, such as sudo or a known installer.

NotePre-approves every shell command (allowed-tools: Bash)SKILL.md
```
allowed-tools: Bash, Read
```

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

Without a licence we can't republish the file, so here is its outline and opening line. It has 69 words (~1,593 tokens).

name: nix-debug
allowed-tools: Bash, Read

Outline of SKILL.md

Nix Deep Debugging
nix eval - Complete Reference
nix repl - Interactive Debugging
REPL Commands
REPL Introspection Patterns
Built-in Debug Functions
builtins.trace
lib.debug Functions
Debugging Assertions
Interactive Debugger (Nix 2.9+)
Debugger Commands
Trigger Debugger Programmatically
nix-instantiate - Deep Evaluation
Derivation Debugging
Error Diagnosis Cookbook
"infinite recursion encountered"
"attribute 'x' missing"
"called with unexpected argument 'x'"
"cannot coerce X to string"
"is not a function"
Module System Debugging
Performance Debugging
Quick Debug Snippets

Read the full SKILL.md on GitHub

Files

Just SKILL.md in .claude/skills/nix/debug of r17x/universe.

Open the folder on GitHubat commit 489dbda

Compare with similar skills

Nix Debug next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Nix Debug compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Nix Debug this skillr17x/universe	151	—	~1.6k	Automated safety check: Notes	None	4 days ago
Trellis Session Insightmindfold-ai/Trellis	15k	4 repos	~1.7k	Automated safety check: Pass	AGPL-3.0	9 days ago
Native Data FetchingCherryHQ/cherry-studio-app	4k	6 repos	~2.9k	Automated safety check: Notes	MIT	today
Debugging Executionsn8n-io/n8n	207k	—	~2.6k	Automated safety check: Pass	Custom licence	today
Aoti Debugpytorch/pytorch	104k	1 repos	~1.7k	Automated safety check: Pass	Custom licence	today
Herdr Throwaway Reproductionherdrdev/herdr	43k	—	~2.4k	Automated safety check: Pass	Apache-2.0	today

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Trellis Session Insight
mindfold-ai/Trellis
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15k GitHub starsUsed in 4 repos~1.7k tokens
DevelopmentAuto-check passed
Native Data Fetching
CherryHQ/cherry-studio-app
A skill your agent uses when implementing or debugging ANY network request, API call, or data fetching.
4k GitHub starsUsed in 6 repos~2.9k tokens
DevelopmentAuto-check: notes
Debugging Executions
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Official
Debug failed or wrong-output workflow executions using executions tools.
207k GitHub stars~2.6k tokensUpdated today
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Aoti Debug
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Debug AOTInductor (AOTI) errors and crashes. An agent skill from pytorch/pytorch.
104k GitHub starsUsed in 1 repo~1.7k tokens
DevelopmentAuto-check passed
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43k GitHub stars~2.4k tokensUpdated today
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Questions about Nix Debug

What does Nix Debug do?

Deep debugging of Nix expressions, evaluation, and derivations. Nix Debug is an agent skill from r17x/universe.

When should I use Nix Debug?

Nix Debug fits situations like: tasks that involve Debugging.

How do I install Nix Debug in Claude Code?

Run `npx skills add r17x/universe --skill nix-debug -a claude-code`. Or copy the skill folder (.claude/skills/nix/debug in r17x/universe) into .claude/skills/nix-debug in your project. Claude Code loads it when a task matches its description.

How do I install Nix Debug in Codex?

Run `npx skills add r17x/universe --skill nix-debug -a codex`. Or copy the skill folder (.claude/skills/nix/debug in r17x/universe) into .agents/skills/nix-debug in your project. Codex loads it when a task matches its description.

Can I use Nix Debug in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add r17x/universe --skill nix-debug -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/nix-debug, .gemini/skills/nix-debug, .github/skills/nix-debug and .opencode/skills/nix-debug in your project.

What does Nix Debug need to run?

Going by SKILL.md and its folder, Nix Debug needs the command-line tools its instructions call (nix and jq). Its frontmatter pre-approves these tools: Bash, Read.

Does Nix Debug access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Nix Debug safe to install?

Our automated static check of SKILL.md found notes only (pre-approves every shell command (allowed-tools: bash)), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.

What licence does Nix Debug use?

No licence was found for Nix Debug or its repository. Without one, default copyright applies: ask the author before reusing or redistributing it.

How many tokens does Nix Debug use?

About 1.6k tokens (SKILL.md is roughly 6.4k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Nix Debug?

Skills that share tags, products or a category with Nix Debug: Trellis Session Insight (mindfold-ai/Trellis, 15k stars), Native Data Fetching (CherryHQ/cherry-studio-app, 4k stars), Debugging Executions (n8n-io/n8n, 207k stars) and Aoti Debug (pytorch/pytorch, 104k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Nix Debug?

r17x (a GitHub user) maintains it in r17x/universe, which has 151 GitHub stars. The repository holds 5 skills in this directory. The repository was last updated on October 4, 2026.

Source: r17x/universe on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Nix Debug

Install Nix Debug

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Files

Compare with similar skills

Similar skills

Trellis Session Insight

Native Data Fetching

Debugging Executions

Aoti Debug

Herdr Throwaway Reproduction

Systematic Debugging

More from r17x/universe

Nix

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Questions about Nix Debug

Install Nix Debug

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Files

Compare with similar skills

Similar skills

More from r17x/universe

Related

Questions about Nix Debug