I built a local heuristic to catch AI sounding product copy. Here is what it actually catches and what it misses.

This week I packaged a small analyzer I had been testing as a Chrome extension: Copy Tell. It checks product descriptions and posts on Gumroad and Substack for the kind of stock phrasing an unedited AI writing tool tends to produce, and shows a small notice if enough of it shows up.

No ML model. Pure lexical and stylometric scoring: stock phrase density, symmetric list framing used as filler, sentence length uniformity, a few other signals. Everything runs in the page's own JavaScript context. Nothing is sent anywhere.

I tested it against a 100 sample labeled set: 50 AI generated product descriptions, 50 real human written descriptions pulled from published npm package READMEs.

Results:

tp 39, fp 1, tn 49, fn 11