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SkillPicked

Skill Creator

Skill Creator (skill-creator) is a skill by Anthropic that helps you write a new agent skill, test it against real prompts, and improve it, including the description that decides when the skill triggers.

Notes by Lior Pesoa · Updated · Works with Claude Code

Made by Anthropic.

Source: github.com/anthropics/skills · Apache-2.0 license. Everything below is my review: I tested it myself.

Original ↗ (opens in a new tab)
npx skills add anthropics/skills --skill skill-creator

Raw for agents: /library/skill-creator.md

Verdict

7/10

My score

It makes the agent test what it builds and write a description that triggers reliably. Its full evaluation loop is built for an interactive session, so a one-shot request only gets part of the value.

Tested

Pros

  • Tested the skill's helper script against four cases (no tags, nothing new, normal commits, a bad path) before handing it over.
  • Wrote a description that lists the ways people actually ask, so the skill triggers even when you don't say "release notes".
  • Shorter skill file for the same coverage: 62 lines against 92.
  • Made by Anthropic and free under the Apache-2.0 license.

Cons

  • In a one-shot run it didn't do its signature step: running test prompts with and without the new skill and comparing them.
  • The skill without it was already good. Both had the same structure, rules and helper script.
  • Its full loop runs extra agent sessions, which adds time and cost when you use it properly.
Best for
Turning a workflow you repeat into a skill, especially when you'll iterate on it in a live session.
Skip it if
You only need a quick SKILL.md for yourself and don't mind tuning it by hand.

The test

Same task, both runs

Create an agent skill that writes short App Store release notes from the git log since the last tag. Put the skill folder in ./release-notes/ in the current directory.

Without the skill48 s · $0.16
  • SKILL.md: 92 lines, plus a commits-since-tag script
  • Description: names 4 kinds of request
  • Helper script not tested (test commands were blocked)
With skill-creator54 s · $0.19
  • SKILL.md: 62 lines, plus a commits-since-tag script
  • Description: names 8 kinds of request, including "what changed since the last version"
  • Helper script tested on 4 cases, all passed

What I found

  • Both runs produced a working skill with the same plan: collect commits, drop internal changes, write 3–6 plain-text bullets.
  • With the skill, the agent wrote its tests as a single script it was allowed to run, so it actually tested its work. Without it, the agent's test commands were blocked and it handed over untested code.
  • The biggest visible difference is the description, which decides when a skill loads. skill-creator's version covers far more of the ways people ask.

How I ran it: Claude Code 2.1.306 with Claude Opus, run headless twice with only Claude Code's built-in skills loaded (no user skills, plugins or MCP servers). The second run had skill-creator installed in the project and its prompt started with "Use the skill-creator skill." Both runs could run git and shell scripts in the test folder.

What it does

  • Interviews you about what the skill should do, then drafts the SKILL.md.
  • Writes test prompts and runs them with the skill loaded, so you can see what it actually does.
  • Grades and compares the runs, and shows the results in a review page you can read side by side.
  • Rewrites the skill's description so it triggers on the right requests and stays quiet on the wrong ones.

When to use it

Use it when you've explained the same workflow to your agent more than twice, or when a skill you already have triggers at the wrong times.

How it works

  1. 01Decide what the skill should do and roughly how.
  2. 02Draft the skill.
  3. 03Run a few test prompts with the skill loaded.
  4. 04Review the results, qualitatively and with simple evals.
  5. 05Rewrite and repeat, then widen the test set.

Questions

Who made skill-creator?

Anthropic. It's published in github.com/anthropics/skills under the Apache-2.0 license. This page is my review of it.

How do I install skill-creator in Claude Code?

Run this in your project:

npx skills add anthropics/skills --skill skill-creator

Or, inside Claude Code, run:

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

Do I need it to write a skill?

No. A skill is a folder with a SKILL.md file, and you can write one by hand. skill-creator helps you test it and tune when it triggers.