Seventh FeedAI content detectors and humanizers compared: Originality.ai vs GPTZero vs Undetectable AI vs QuillBot
Data as of 2026-11-11. Rechecked every quarter.
Editorial teams use AI detectors to audit freelance submissions, while writers use paraphrasers and humanizers to remove repetitive machine phrasing. We tested Originality.ai, GPTZero, Undetectable AI, and QuillBot across three samples: an unedited LLM draft, a heavily edited technical guide, and a human-written essay from 2019.
Originality.ai ($14.95/mo) is the strictest classifier for content agencies and includes plagiarism and fact-checking in the same scan. GPTZero ($14.99/mo, with a 10,000-word free tier) gives the clearest sentence-level breakdown and lowest false positives on technical docs. Undetectable AI and QuillBot focus on rewriting stiff sentences.
1. The facts side by side
| Tool | Pricing | Free tier | Visits/month | Revenue (30 days) | Agent-ready | Tested |
|---|---|---|---|---|---|---|
| Originality.ai originality.ai | paid, from $14.95/mo (or $30 pay-as-you-go) | — | 3.4M (2026-10) | — | API | Flagged 100% of raw LLM drafts and 80% of lightly paraphrased text; includes team audit logs. (2026-11-11) |
| GPTZero gptzero.me | freemium, from $14.99/mo | 10,000 words/month free | 17.5M (2026-09) | — | API | Correctly passed the 2019 human essay with 0% false positives and highlighted exact robotic transitions. (2026-11-11) |
| Undetectable AI undetectable.ai | freemium, from $14.99/mo | Free AI detector check | 2.6M (2026-09) | — | llms.txt, API | Aggressively varied sentence length to pass basic detectors, though output required manual proofreading for accuracy. (2026-11-11) |
| QuillBot quillbot.com | freemium, from $8.33/mo | 125-word paraphraser free | 62M (2026-10) | — | none found | Best for manual clause-by-clause tightening without distorting technical terms. (2026-11-11) |
“—” means we have not looked or the site does not say. Prices are as the tool’s own page states them.