On the bundled sample: 14 findings (8 errors, 5 warnings, 1 info) in 1 file from 19 rules, including “Apache 2.0” for Apache-2.0 and a setuptools>=61.0 pin.

Who it’s for
For Python library maintainers and teams who publish to PyPI and are moving license metadata to PEP 639.

What breaks, and when
Under PEP 639 setuptools refuses an SPDX license next to a License :: classifier and the build stops; Python 3.8 support ended 2024-10-07 and Python 3.10 reaches end of life on 2026-10-31.

What you get
• SKILL.md, an offline Node scanner and the 19-rule table

See it first
The real output of the bundled example is on getreadystack.com/skills/pyproject-pep-639-release-check/ — free, no sign-up, so you see what it finds before you pay.

Install in 30 seconds
Unzip into ~/.claude/skills/, then ask Claude Code: “I’m about to publish a new release of our Python library to PyPI. Can you check our pyproject.toml packaging metadata for anything the build or PyPI will reject, especially the license fields? Don’t edit anything yet.”. Needs Node 16+.

What it does not do
Does not build your package, run pip or call PyPI; not license advice.

FAQ
Q: How is this different from asking Claude without the skill?
A: The skill carries a dated rule table and a scanner that reads every file, so Claude quotes the exact date and line instead of guessing from memory.
Q: How do I get the files?
A: In your Whop library after paying: the lesson “pyproject-pep-639-release-check.zip”.