Copy Tell - AI Description Checker

Flags Gumroad/Substack copy reading like AI output. Runs locally. 88% accurate on AI-vs-docs text, untested on marketplace copy.

Copy Tell checks product descriptions and posts on Gumroad and Substack for the kind of stock phrasing an unedited AI writing tool tends to produce - "unlock the power of," "seamlessly," "whether you're a beginner or an expert," rule-of-three lists used as filler, and a few other patterns. When it finds enough of them, it shows a small notice above the text so you can decide for yourself whether it needs a second look. You can also paste any text into the extension's own popup to check it directly, without visiting a supported page at all. **How well it actually works, measured honestly:** 88% overall accuracy on a 100-sample test set - 50 AI-generated product descriptions (written by the same model that built this tool) versus 50 real human-written descriptions pulled from published npm package READMEs. That test set is AI-generated text versus real technical documentation, **not real Gumroad or Substack marketplace listing copy** - it has not yet been validated against real seller copy, which tends to carry more superlatives and rule-of-three phrasing than plain technical writing does, so real-world precision on marketplace listings specifically may run lower than the numbers below. Full source list: `CITATIONS.md`. Broken down: it correctly flagged AI text 97.5% of the time it made a positive call (1 false positive out of 40 positive calls), and caught 78% of the AI samples overall (missed 11 of 50). The 11 it missed were all written in a plainer, more literal register with no stock phrases to catch - a real and expected blind spot of a rule-based checker like this one. Treat this as one signal, never a verdict: a low score doesn't mean text is definitely human-written, and a flag doesn't mean it definitely isn't. **What it does with your data:** nothing leaves your browser. The check runs entirely in JavaScript on the page you're viewing or the text you paste; no network requests, no accounts, no analytics, no storage beyond what the page itself already has open. **Where it works:** built for Gumroad product pages and Substack posts. Spot-checked against real, live pages on 2026-08-20: the Substack selectors correctly find the post body on a real page. Gumroad's product description has no stable CSS class to target at all (confirmed against a live listing), so on Gumroad the extension always uses its largest-text-block fallback instead - confirmed on the same check to correctly find the real description text, with some surrounding price text the analyzer's phrase-matching tolerates fine. Either way - specific selector match or fallback - the extension finds something reasonable rather than doing nothing. ## Privacy practices disclosure (Chrome Web Store form fields) - Does this extension collect or transmit user data? No. - Does this extension use remote code? No - all code ships in the extension package.