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Agent skill

Skill Creator

by Zfinix in Zfinix/aster

Turning a workflow this session learned into a reusable skill.

Apache-2.0Auto-check passedAgent Workflows

Install Skill Creator

skills CLI
$ npx skills add Zfinix/aster --skill skill-creator -a claude-code

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

GitHub CLI
$ gh skill install Zfinix/aster skill-creator --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/Zfinix/aster.git skills-src && mkdir -p .claude/skills && cp -r skills-src/crates/aster-skills/builtins/skill-creator .claude/skills/skill-creator && 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/

Facts

Skill name
skill-creator
GitHub stars
112
Token cost
~999 tokens
SKILL.md length
533 words
Files
1
Skills in repo
19
Repo updated
First seen
Licence
Apache-2.0

At a glance

Turning a workflow this session learned into a reusable skill.

  • Works in 9 steps: Check the index first. If an existing… → Confirm before creating. A skill is a… → Pick the root by scope. Project-specific… → …
  • The user says save this as a skill
  • Calls git
  • Make a skill for this

What it does

Skill Creator is an agent skill from Zfinix/aster. Turning a workflow this session learned into a reusable skill. Use when the user says save this as a skill or make a skill for this, when they repeat the same correction or instructions a second time, or when a multi-step procedure just worked and will clearly recur.

Its SKILL.md is about 1000 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 Agent Workflows, covering Skill authoring. The repository describes itself as: An open-source agent harness for software work. The licence is Apache-2.0.

When your agent uses it

  • The user says save this as a skill
  • Make a skill for this
  • They repeat the same correction
  • Instructions a second time

Example prompts

  • “/skill-creator”

Workflow steps

9 steps, taken from the first numbered list in SKILL.md.

  1. Check the index first. If an existing skill already covers the
  2. Confirm before creating. A skill is a repo or config file; say what
  3. Pick the root by scope. Project-specific workflow
  4. The description is the trigger, so write it as one. The index shows
  5. Body format: numbered imperative rules with counter-examples. Each
  6. Capture the evidence, not the theory. Put in the exact commands that
  7. Keep it small. A few hundred to a couple thousand words. Past that,
  8. Frontmatter is exactly name and description between --- fences,
  9. Corrections are skill fuel. When the user corrects the same thing a

What it can do on your machine

Read from SKILL.md and the folder at commit 3fbb67c. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Shell commands in SKILL.md call:

    • git

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md. Its commands use git, which can reach the network depending on how they are called.

    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

Skill Creator loads about 999 tokens when it runs. Until then it costs about 70 tokens; SKILL.md has 533 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~70
When it runs · the whole SKILL.md, loaded when a task matches
~999

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 passed

The automated check found no risky patterns in SKILL.md.

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

The full file from Zfinix/aster at commit 3fbb67c, republished under its Apache-2.0 licence (© Zfinix). 533 words, ~999 tokens.

Download SKILL.mdSave it as .claude/skills/skill-creator/SKILL.md (or your agent's skills folder).
name
skill-creator
description
Turning a workflow this session learned into a reusable skill. Use when the user says save this as a skill or make a skill for this, when they repeat the same correction or instructions a second time, or when a multi-step procedure just worked and will clearly recur.

Skill creator

  1. Check the index first. If an existing skill already covers the workflow, extend that skill's file instead of creating a near-duplicate.
  2. Confirm before creating. A skill is a repo or config file; say what you are about to write and where, and get a yes. Exception: the user already asked for the skill in this turn.
  3. Pick the root by scope. Project-specific workflow: .aster/skills/<name>/SKILL.md in the repo. Personal preference that applies everywhere: <aster home>/skills/<name>/SKILL.md. Kebab-case name, under 64 characters.
  4. The description is the trigger, so write it as one. The index shows only name and description; the body loads when a request matches. State what the skill does, then the concrete situations that should fire it: "Use when the user asks to X, mentions Y, or a Z fails."
  5. Body format: numbered imperative rules with counter-examples. Each rule is one behavior, stated as a command, with a literal do-this and never-this where it helps. Write "Stage named files: git add src/a.rs. Never git add -A." Never write essays about philosophy.
  6. Capture the evidence, not the theory. Put in the exact commands that worked this session, the failure that motivated the rule, and the check that proves the workflow succeeded. A skill mined from a real session beats one written from imagination.
  7. Keep it small. A few hundred to a couple thousand words. Past that, split into two skills with distinct triggers.
  8. Frontmatter is exactly name and description between --- fences, then the markdown body. Verify after writing: the skill should appear in the index next session, and read_skill should return the body now.
  9. Corrections are skill fuel. When the user corrects the same thing a second time, that is the signal: offer to fold it into a skill or a remember note so they never repeat it again.
Show full SKILL.md (225 more words)Show less

Loader rules and tooling

Validation enforced by aster's loader: the file must open with a --- frontmatter fence; description is required, non-empty, max 1024 characters; name is optional (falls back to the directory name) but when present must be lowercase letters, digits, and hyphens, max 64 characters.

always: true is for a skill with no "when": one that governs every message of a session, such as a harness where the device is the whole subject. Its body goes into the system prompt once, it is left out of the list the model scans, and read_skill on it just says it is already loaded. Everything else stays on-demand: an always-on skill spends its tokens on every turn whether or not the turn needs it.

Scaffold and lint from the CLI:

sh
aster skills init my-skill                            # scaffold my-skill/SKILL.md
aster skills add ./my-skill -l                        # validate: listed if it parses, warns if not
aster skills add ./my-skill --all --yes --force       # install user-global, live next turn
aster skills add ./my-skill --all --yes --force -p    # or into this project only

add -l against a local path is the fastest check: a skill that does not appear in the listing failed frontmatter validation.

Install a skill the moment it is written, and again after every edit; --all is required when no terminal is attached and --force replaces the installed copy. Do not save a memory about a skill you wrote: the skill is the record.

To publish a skills repo, host one subdirectory per skill under skills/ (skills/my-skill/SKILL.md); consumers install with aster skills add owner/repo. Names must be unique within a repo; on collision the first found wins.

© Zfinix, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in crates/aster-skills/builtins/skill-creator of Zfinix/aster.

Open the folder on GitHubat commit 3fbb67c

Compare with similar skills

Skill Creator 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.

Skill Creator compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Skill Creator this skillZfinix/aster112—~999Automated safety check: PassApache-2.0
Skill CreatorAzure/azqr79589 repos~8.2kAutomated safety check: PassApache-2.0
Claude Code Skill Developer Guidediet103/claude-code-infrastructure-showcase10k11 repos~3.5kAutomated safety check: PassMIT
Darwin Skill Optimizeralchaincyf/darwin-skill6.2k1 repos~4.7kAutomated safety check: PassMIT
Claude Code Command Developmentanthropics/claude-plugins-official38k10 repos~4.8kAutomated safety check: PassApache-2.0
Claude Code Plugin Structureanthropics/claude-plugins-official38k10 repos~3.4kAutomated safety check: PassApache-2.0

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Categories

Questions about Skill Creator

What does Skill Creator do?

Turning a workflow this session learned into a reusable skill. Skill Creator is an agent skill from Zfinix/aster. Turning a workflow this session learned into a reusable skill.

When should I use Skill Creator?

Skill Creator fits situations like: the user says save this as a skill; make a skill for this; they repeat the same correction; instructions a second time.

How do I install Skill Creator in Claude Code?

Run `npx skills add Zfinix/aster --skill skill-creator -a claude-code`. Or copy the skill folder (crates/aster-skills/builtins/skill-creator in Zfinix/aster) into .claude/skills/skill-creator in your project. Claude Code loads it when a task matches its description.

How do I install Skill Creator in Codex?

Run `npx skills add Zfinix/aster --skill skill-creator -a codex`. Or copy the skill folder (crates/aster-skills/builtins/skill-creator in Zfinix/aster) into .agents/skills/skill-creator in your project. Codex loads it when a task matches its description.

Can I use Skill Creator 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 Zfinix/aster --skill skill-creator -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/skill-creator, .gemini/skills/skill-creator, .github/skills/skill-creator and .opencode/skills/skill-creator in your project.

What does Skill Creator need to run?

Going by SKILL.md and its folder, Skill Creator needs the command-line tools its instructions call (git).

Does Skill Creator access the network?

SKILL.md contains no URLs. Its commands use git, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is Skill Creator safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Skill Creator use?

Skill Creator is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Skill Creator use?

About 999 tokens (SKILL.md is roughly 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 Skill Creator?

Skills that share tags, products or a category with Skill Creator: Skill Creator (Azure/azqr, 795 stars), Claude Code Skill Developer Guide (diet103/claude-code-infrastructure-showcase, 10k stars), Darwin Skill Optimizer (alchaincyf/darwin-skill, 6.2k stars) and Claude Code Command Development (anthropics/claude-plugins-official, 38k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Skill Creator?

Zfinix (a GitHub user) maintains it in Zfinix/aster, which has 112 GitHub stars. The repository holds 19 skills in this directory. The repository was last updated on October 6, 2026.

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