Claude skill-creator

Writing a skill is easy. Writing one that triggers at the right moment and produces the same quality every time takes testing. Anthropic's skill-creator is a Claude skill builder that turns that testing into a process Claude runs with you. Its description starts plainly: create new skills, modify and improve existing skills, and measure skill performance. If you have not written a skill before, read how Claude Skills work first.

What the skill does

The SKILL.md in Anthropic's repository walks Claude through these stages:

1. Capture intent. Claude asks what the skill should do, when it should trigger, what the output looks like and whether test cases make sense. It looks into edge cases and formats before writing.
2. Write the SKILL.md. Claude drafts the front matter and instructions. The guide asks for a description that names both the job and the situations that should trigger it, and a body under 500 lines, with longer material moved into bundled files.
3. Write test cases. Two or three realistic prompts go into evals/evals.json.
4. Run and compare. In Claude Code, Claude starts two subagents per test, one with the skill and one without, then grades both against the checks it drafted.
5. Review. A bundled viewer shows the outputs, grades, pass rates, time and tokens side by side, and saves your feedback.
6. Iterate. Claude revises the skill from your feedback and reruns the tests into a new folder, until you are satisfied.
7. Tune the description (optional). Claude writes 20 trigger queries, roughly half that should fire the skill and half that should not, and runs a loop that rewrites the description to fire on the right ones.
8. Package. A script bundles the finished skill into a .skill file you can install.

The guide pushes against overfitting. A skill that only works on its test examples is useless, so fixes should address patterns that repeat across the feedback.

Who publishes it

Anthropic. It is in the anthropics/skills repository as part of the example-skills set, and in Anthropic's official Claude Code plugin directory as a standalone skill-creator plugin.

Where it works

The SKILL.md describes three environments, and the full workflow runs only in one of them:

Description tuning needs the claude -p command line. The guide says it works in Claude Code and Cowork, and tells Claude to skip it on Claude.ai.

How to install it

To use it as a Claude Code skill builder, install it from Anthropic's official marketplace:

/plugin install skill-creator@claude-plugins-official

Or install Anthropic's full example set:

/plugin marketplace add anthropics/skills
/plugin install example-skills@anthropic-agent-skills

In Claude.ai, the anthropics/skills README says the example skills are already available on paid plans. Turn on "Code execution and file creation" under Settings > Capabilities, then check Customize > Skills.

Use the skill-creator skill. I want a skill that [what the skill should do].

It should trigger when I [situations or phrases].
It should not trigger when I [similar requests that are a different job].
A good output looks like this: [paste one example].

Interview me about anything unclear before you write the SKILL.md, then propose three test prompts.

When it helps

• You have a routine you explain to Claude over and over: a report format, a review checklist, a house style.
• An existing skill fires on the wrong requests, or never fires.
• You want evidence that a skill improves results, measured against the same prompts without it.

For simpler cases you may not need it. A one-page SKILL.md written from the template in our Claude Skills manual is often enough. If what you need is a better single prompt and not a reusable skill, try our Claude prompt generator.

Limits

• Claude.ai gets a reduced version. Without subagents, there is no with-and-without comparison and no automated description tuning.
• Short requests may not trigger skills. The guide notes that simple one-step queries may not trigger a skill even when the description matches, so test prompts should be substantive.
• Testing costs usage. In Claude Code every test runs twice, once with and once without the skill, and description tuning runs several rounds.

Once you have a skill, keep the commands for running it handy with our Claude Code cheat sheet, and browse other skills in the Claude Skills catalog.

FAQ

Is skill-creator built into Claude?

In Claude Code you install it as a plugin. In Claude.ai, Anthropic's repository says the example skills, which include skill-creator, are available on paid plans.

Can skill-creator improve a skill I already have?

Yes. Its description covers modifying and improving existing skills, and the test and iterate loop works on any SKILL.md you give it.

What file does it produce?

A skill folder with SKILL.md and any bundled files, which its packaging script can bundle into a .skill file.

Is there a skill creator for Codex?

Codex has its own, made by OpenAI. Its docs say to invoke $skill-creator in Codex, which guides you through the skill's purpose, triggers and scripts. Because both tools read the same SKILL.md format, a skill built with either one can usually be copied to the other. Check each tool's docs for fields only it reads.