skill-creator-plus

A free Claude skill that audits, builds and improves other skills against Anthropic's own skill-writing rules, including what changed for the newest Claude models.

Point it at a skill (or a whole folder of skills) and it gives you a findings report first: every rule marked pass, fail or not applicable, with the file and line as evidence and a proposed fix. It changes nothing until you say which fixes to apply.

Why this matters now

A skill is a folder with a SKILL.md file that teaches Claude how to do a job the same way each time. Anthropic publishes clear rules for writing them, and it is easy to break several without noticing: descriptions that never trigger, reference files Claude only half reads, rules buried where compaction cuts them.

The core rules on Anthropic's skill authoring page have been stable for about a year. What changed is the models:

• The prompting guide for Claude Fable 5 says skills written for older models are often too prescriptive and can make output worse. Review them and remove what the model now does better on its own, but test before you delete.
• The guides for Fable 5, Opus 5.5 and Sonnet 5.5 all list a reasoning_extraction refusal: asking Claude to write out its reasoning in the reply can be declined. A short explanation of the answer is fine.
• The Fable 5 guide also says to give the reason, not only the request, to steer with brief instructions instead of long lists, and to make checking explicit, preferring a fresh Claude as the checker over self-review.

Claude Code adds its own: put the most important instructions at the top of SKILL.md (compaction keeps only the first 5,000 tokens), and move any rule that has to hold on every run into a hook.

This skill checks all of that, and the validator script checks the mechanical parts in a second.

Install

Claude Code. Put the folder in your skills folder and name it skill-creator-plus:

# for all your projects
git clone https://github.com/robonuggets/skill-creator-plus ~/.claude/skills/skill-creator-plus

# or for one project only, from the project folder
git clone https://github.com/robonuggets/skill-creator-plus .claude/skills/skill-creator-plus

On Windows, ~/.claude is the .claude folder inside your user folder. Downloading the ZIP from GitHub and copying the folder there works too.

claude.ai. Zip the folder (SKILL.md, references/, scripts/ and LICENSE; you can leave out examples/) and upload it under Skills in claude.ai settings. The frontmatter uses only the fields claude.ai accepts. The validator needs code execution turned on.

Use it

Just ask in plain words. Three modes:

"Improve my skill for Opus 5.5" runs AUDIT, then REFINE with the fixes you approve.

See examples/pdf-helper-report.md for a full audit of a deliberately broken sample skill.

The validator

scripts/validate_skill.py checks the rules a script can check. Python 3.8 or newer, standard library only, works on Windows, Mac and Linux.

python3 scripts/validate_skill.py path/to/my-skill              # one skill
python3 scripts/validate_skill.py --all ~/.claude/skills         # every skill in a folder, one table
python3 scripts/validate_skill.py path/to/my-skill --json       # machine-readable
python3 scripts/validate_skill.py path/to/my-skill --ban-em-dash # also flag em dashes
python3 scripts/init_skill.py my-new-skill --path ~/.claude/skills --refs --scripts

Exit codes: 0 no errors (warnings and notes are fine), 1 errors found, 2 could not run. Each finding carries a rule ID from the table below.

Part of the real output for the sample skill in examples/pdf-helper/:

Skill: examples/pdf-helper (name: Claude_PDF_Helper)

ERROR  FM1    SKILL.md:4  'description' has an unquoted ': ' (or ends with ':'), which YAML reads as a new key, so the frontmatter will not parse. Wrap the value in double quotes.
ERROR  ST4    reference/advanced.md:3  reference/details.md is reached only through other reference files (reference/advanced.md:3), never from SKILL.md. Claude may only preview files it reaches that way (for example with head -100). Link it from SKILL.md, or fold its content into the file that needs it.
ERROR  ST5    reference/api.md  reference/api.md is 124 lines with no contents list in its first 50 lines. Add a '## Contents' list at the top so a partial read still shows everything the file covers.
WARN   DS2    SKILL.md:4  description is not in third person (found "I can"). It is injected into the system prompt; write "Processes Excel files", not "I can help" or "You can use this".
WARN   NM2    SKILL.md:20  asks Claude to write out its reasoning ("Think step by step and write"). Newer models (Claude Fable 5, Opus 5.5, Sonnet 5.5) may decline this with the reasoning_extraction refusal. Ask for the answer, or a short explanation of it, instead.
NOTE   HK1    SKILL.md:11,31  words like "must always" mark a rule that must hold every time, and the frontmatter has no hooks. Prose can be skipped or cut by compaction; if the rule truly must hold, enforce it with a hook (frontmatter hooks:).
...
Result: 8 errors, 11 warnings, 6 notes - fix the errors first.

The full output is in examples/pdf-helper-validator-output.txt. With --all you get one table:

Skill       Errors  Warnings  Notes  Rules with errors or warnings
----------  ------  --------  -----  -----------------------------
pdf-helper       8        11      6  FM1 FM2 ST4 ST5

The rules

46 rules. Script means the validator decides. Script + read means the validator flags candidates and Claude confirms in context. Read means Claude judges it during an audit and cites the evidence. "Advice" marks rules from practice rather than from Anthropic's docs.

Rules were checked against Anthropic's pages on 2026-10-05.

What is in the box

SKILL.md                      the skill: rules, the three modes, links to the rest
references/audit-checklist.md every rule with why, how to check, and the report format
references/authoring-guide.md how to write each part of a skill
references/testing.md         evaluations, baselines, model sweeps, test before you delete
scripts/validate_skill.py     the validator
scripts/init_skill.py         scaffolds a new skill that passes the validator
examples/                     a broken sample skill, its validator output and its audit report

Credits and license

The failure-mode names used in audits (no-op, duplication, sediment, sprawl, premature completion) come from Matt Pocock's "writing-great-skills". Not affiliated with Anthropic. MIT license, see LICENSE.

Made by RoboNuggets