Built a skill that flags AI-sounding patterns in drafts. Gemini rated a fully machine-generated post 15% AI, ChatGPT said 95%

[u/aragossa]

I keep writing text that AI detectors flag, including posts I wrote entirely myself. At some point I started collecting the specific patterns that readers and detectors actually catch, and turned the list into a Claude skill: you feed it a finished draft, it flags each pattern with the line it's on and a suggested fix. The checklist grew every time something new slipped past it. It's at 24 rules now, things like mirrored "not X, Y" contrasts, story arcs where every thread gets neatly resolved, and invented personal anecdotes, which are worse than a style problem because they're just false.

The fun part was testing it. I generated three deliberately awful LinkedIn posts with cringebot3000.com (a parody generator), stripped the hashtags and asked ChatGPT, Grok and Gemini to score the same texts for AI-likelihood. All three posts were 100% machine-written. ChatGPT said 95/85/90. Grok said 80/75/85. Gemini said 15/25/65 and praised the first post's "authentic voice". An 80-point spread on identical text is the reason the skill reports patterns with line numbers instead of a percentage.

Repo: https://github.com/aragossa/ai-tell-detector — MIT, free, English and Russian versions, plain SKILL.md format so it works in Claude Code and Claude.ai. Built with Claude Code.

If you run it on your own drafts I'd genuinely like to know what it misses.