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Agent skill

Aster Skill Authoring

by Zfinix in Zfinix/aster

Author skills for aster (and Claude Code): SKILL.md format, frontmatter rules, name/description validation limits, folder layout, scaffolding with aster skills init, and local testing with aster…

Apache-2.0Auto-check passedAgent Workflows

Install Aster Skill Authoring

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

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

GitHub CLI
$ gh skill install Zfinix/aster aster-skill-authoring --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/skills/aster-skill-authoring .claude/skills/aster-skill-authoring && 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
aster-skill-authoring
GitHub stars
113
Token cost
~769 tokens
SKILL.md length
315 words
Files
1
Skills in repo
19
Repo updated
First seen
Licence
Apache-2.0

At a glance

Author skills for aster (and Claude Code): SKILL.md format, frontmatter rules, name/description validation limits, folder layout, scaffolding with aster skills init, and local testing with aster…

  • Writing a new SKILL.md
  • SKILL.md covers Format, Writing a good description, Workflow and After writing a skill, plus 2 more sections
  • Calls npx
  • Fixing a skill that fails to load

What it does

Aster Skill Authoring is an agent skill from Zfinix/aster. Author skills for aster (and Claude Code): SKILL.md format, frontmatter rules, name/description validation limits, folder layout, scaffolding with aster skills init, and local testing with aster skills add -l. Use when writing a new SKILL.md, fixing a skill that fails to load, or publishing a skills repo.

Its SKILL.md is about 770 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 and Project scaffolding. The repository describes itself as: An open-source agent harness for software work. The licence is Apache-2.0.

When your agent uses it

  • Writing a new SKILL.md
  • Fixing a skill that fails to load
  • Publishing a skills repo

Example prompts

  • “/aster-skill-authoring”

Requirements

  • Node.js

What it can do on your machine

Read from SKILL.md and the folder at commit f77a5b4. 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:

    • npx

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

  • Network

    No URLs in SKILL.md. Its commands use npx, 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

Aster Skill Authoring loads about 769 tokens when it runs. Until then it costs about 83 tokens; SKILL.md has 315 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~83
When it runs · the whole SKILL.md, loaded when a task matches
~769

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 f77a5b4, republished under its Apache-2.0 licence (© Zfinix). 315 words, ~769 tokens.

Download SKILL.mdSave it as .claude/skills/aster-skill-authoring/SKILL.md (or your agent's skills folder).
name
aster-skill-authoring
description
Author skills for aster (and Claude Code): SKILL.md format, frontmatter rules, name/description validation limits, folder layout, scaffolding with `aster skills init`, and local testing with `aster skills add -l`. Use when writing a new SKILL.md, fixing a skill that fails to load, or publishing a skills repo.

Authoring skills

A skill is a directory containing a SKILL.md: YAML frontmatter with name and description, then a markdown body of instructions. The directory may bundle extra resources (scripts, references); the whole directory is copied on install.

Format

markdown
---
name: my-skill
description: One or two sentences saying what it does and when to use it.
---

# My skill

Instructions the agent follows when the skill triggers...

Validation rules enforced by aster's loader:

  • 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 only, max 64 characters.
  • The file must open with a --- frontmatter fence.

Writing a good description

The description is the trigger: agents read it to decide whether to load the skill. State what the skill covers AND when to use it, and name the concrete commands, files, or phrases that should trigger it. Vague descriptions never fire.

Workflow

sh
aster skills init my-skill      # scaffold my-skill/SKILL.md
# edit my-skill/SKILL.md
aster skills add ./my-skill -l  # validate: lists the skill if it parses, warns if not
aster skills add ./my-skill     # install into .aster/skills to try it

add -l against a local path is the fastest lint: a skill that doesn't appear in the listing failed frontmatter validation.

After writing a skill

Install it right away so it is live for the next turn, without waiting to be asked:

sh
aster skills add ./my-skill --all --yes --force      # user-global
aster skills add ./my-skill --all --yes --force -p   # this project only (.aster/skills)

Re-run the same command after every edit; --force replaces the installed copy, and --all is required when no terminal is attached (--yes alone is refused). Do not save a memory about the skill you wrote: the skill is the record, and a memory that repeats it is noise.

Repo layout for publishing

Host multiple skills under a skills/ directory, one subdirectory per skill:

text
skills/
  my-first-skill/SKILL.md
  my-second-skill/SKILL.md

Discovery walks up to 6 levels deep and skips .git, node_modules, target, dist, build. Consumers then install with aster skills add owner/repo or npx skills add owner/repo. Skill names must be unique within a repo; on collision the first found wins.

Body guidelines

  • Write for an agent, not a human tutorial: imperative instructions, exact commands, real flag names.
  • Keep it grounded: only document behavior you have verified against the tool's --help or source.
  • Prefer short sections with runnable code blocks over prose.

© 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 skills/aster-skill-authoring of Zfinix/aster.

Open the folder on GitHubat commit f77a5b4

Compare with similar skills

Aster Skill Authoring 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.

Aster Skill Authoring compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Aster Skill Authoring this skillZfinix/aster113—~769Automated safety check: PassApache-2.0
Claude Code Plugin Structureanthropics/claude-plugins-official38k10 repos~3.4kAutomated safety check: PassApache-2.0
Skill Creatorluongnv89/asm954—~5.3kAutomated safety check: PassMIT
Skill ForgeAgriciDaniel/skill-forge179—~1.9kAutomated safety check: NotesMIT
Create Skillmp-web3/claude-starter-kit109—~985Automated safety check: NotesMIT
Skill Forge BuildAgriciDaniel/skill-forge179—~1.3kAutomated safety check: PassMIT

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Categories

Questions about Aster Skill Authoring

What does Aster Skill Authoring do?

Author skills for aster (and Claude Code): SKILL.md format, frontmatter rules, name/description validation limits, folder layout, scaffolding with aster skills init, and local testing with aster…. Aster Skill Authoring is an agent skill from Zfinix/aster.md format, frontmatter rules, name/description validation limits, folder layout, scaffolding with aster skills init, and local testing with aster skills add -l.

When should I use Aster Skill Authoring?

Aster Skill Authoring fits situations like: writing a new SKILL.md; fixing a skill that fails to load; publishing a skills repo.

How do I install Aster Skill Authoring in Claude Code?

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

How do I install Aster Skill Authoring in Codex?

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

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

What does Aster Skill Authoring need to run?

Going by SKILL.md and its folder, Aster Skill Authoring needs the command-line tools its instructions call (npx). Our summary lists: Node.js.

Does Aster Skill Authoring access the network?

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

Is Aster Skill Authoring 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 Aster Skill Authoring use?

Aster Skill Authoring 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 Aster Skill Authoring use?

About 769 tokens (SKILL.md is roughly 3.1k 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 Aster Skill Authoring?

Skills that share tags, products or a category with Aster Skill Authoring: Claude Code Plugin Structure (anthropics/claude-plugins-official, 38k stars), Skill Creator (luongnv89/asm, 954 stars), Skill Forge (AgriciDaniel/skill-forge, 179 stars) and Create Skill (mp-web3/claude-starter-kit, 109 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Aster Skill Authoring?

Zfinix (a GitHub user) maintains it in Zfinix/aster, which has 113 GitHub stars. The repository holds 19 skills in this directory. The repository was last updated on October 9, 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.