On one sample package.json it found 10 findings (6 errors, 3 warnings, 1 info): a beta version, an SVG icon, two bad badges and two Microsoft-only dependencies that return 404 on open-vsx.org.

Who it’s for
For VS Code extension authors who publish to the Visual Studio Marketplace and Open VSX.

What breaks, and when
The vsce docs say global Azure DevOps PATs are retired on December 1, 2026 — a release workflow that still uses one stops publishing — and Microsoft-only dependencies return 404 on open-vsx.org (checked 2026-09-30).

What you get
• Ask Claude “check my extension before I publish it” and it scans package.json…

See it first
The real output of the bundled example is on getreadystack.com/skills/vscode-extension-publish-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: “Can you check whether my VS Code extension will publish cleanly to the Marketplace and Open VSX? Don’t edit anything yet.”. Needs Node 16+.

What it does not do
It does not run vsce or ovsx, log in to a marketplace, read your tokens, or edit files until you agree.

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 “vscode-extension-publish-check.zip”.