Best AI Humanizer 2026: 9 Tools Ranked on GPTZero and ZeroGPT, Every Number With a Screenshot
Published: September 22, 2026 · Maintained by: Rephrasy · Data: ai-humanizer/ai-humanizer-benchmark-2026 (CC BY 4.0) · Full page with all figures: Space
TL;DR
We ranked nine AI humanizers on the two detectors people actually get judged by, GPTZero and ZeroGPT, using four test batches between December 2025 and September 2026. Winner: Rephrasy v4. It is the only tool in the seven-tool test that GPTZero labelled "likely human" (the other six came back "AI paraphrasing" or "AI origin likely"), it passes 9 of 10 fresh documents on both GPTZero and ZeroGPT, and it keeps 0.925 cosine similarity to the input at 1.05x the original length. Runner-up on free tiers: humanizer-ai-text.com (100 % → 0 % on ZeroGPT, run 1). Third: StayUndetectable (100 % → 0 % on ZeroGPT, Lite mode). Everything else in the list passes ZeroGPT and fails GPTZero.
What this page is not: a 750-essay study by a PhD nobody can find, with 225,000 "data points" and no dataset. Every figure below links to a blog post with screenshots or to a row in the CSV. If you get a different number, open a discussion and we will add your row.
Direct answer: which AI humanizer is best in 2026?
Rephrasy v4, on the evidence we can show:
- GPTZero, seven-tool test (Dec 2025): Rephrasy was the only output GPTZero read as likely human. StealthWriter, Undetectable AI, WriteHuman, Clever AI, HumanizeAI Pro and QuillBot all came back as AI.
- v4 release test (Aug 2026): 9 of 10 documents passed GPTZero, 9 of 10 passed ZeroGPT, 250 to 1,000 words each, all ten flagged before humanizing.
- Meaning retention: 0.925 cosine similarity to the input. Length 1.05x. Nothing passes by cutting.
- Model history, GPTZero first-pass rate: v2 34 % → v3 67 % → v4 90 %.
- Workflow: the only humanizer with an MCP connector, so you can humanize, score on GPTZero/Copyleaks/Pangram/ZeroGPT/Winston with your own keys, and re-run inside Claude, ChatGPT or Cursor.
Quick answers
Which AI humanizer passes GPTZero?
In the seven-tool test, only Rephrasy. GPTZero returned "AI paraphrasing" for StealthWriter, Undetectable AI, WriteHuman and QuillBot, "possible AI paraphrasing" for Clever AI, and "AI origin likely" for HumanizeAI Pro. Low ZeroGPT scores did not translate: StealthWriter had the lowest ZeroGPT score of all (3.0 %) and still failed GPTZero.
Which AI humanizer passes ZeroGPT?
Most of them. Five of seven tools got under 15 % in the December test, and both free tools we ran in September hit 0 % on the first run. ZeroGPT is the easy detector. A ZeroGPT pass tells you almost nothing about GPTZero or Turnitin.
Is there a good free AI humanizer?
Two, for short text. humanizer-ai-text.com (100 words per run, no signup) took our 100 % AI paragraph to 0 % on ZeroGPT in run 1 and 27.8 % in run 2. StayUndetectable (500 free words a day, no signup) got 0 % and 10.6 %. Both were "human written" on ZeroGPT both times. GPTZero was not part of the free-tier batch, so no GPTZero verdict is listed for them.
Does a 0 % score mean the text is safe?
No. Humanizers are not deterministic (our free-tool runs varied by 10 to 28 points between two runs on the same input) and detectors now train on humanizer output. Score every output on the detector that will actually judge you, and re-run if needed.
Can QuillBot bypass AI detectors?
Not reliably. 62.1 % on ZeroGPT and "AI paraphrasing" on GPTZero. It swaps vocabulary and keeps sentence skeletons, which is what detectors key on.
How we tested
Four batches. Every number on this page comes from one of them, and every batch is a row set in the dataset.
| Batch | Date | What | Detectors |
|---|---|---|---|
| Seven-tool test | 2025-12-19 | One AI-written article through 7 tools at similar output length | ZeroGPT, GPTZero |
| v3 release test | 2026-01-30 | 100 essays, 50 topics, 600+ detector runs, v2 vs v3 | GPTZero, ZeroGPT, Rephrasy detector |
| v4 release test | 2026-08-10 | 10 fresh 250–1,000-word documents | GPTZero, ZeroGPT |
| Free-tier runs | 2026-09-18 | 100-word paragraph, 2 free tools, 2 runs each, baseline 100 % AI | ZeroGPT |
Rules: same input for every tool in a batch, each detector's own verdict (no "mixed" counted as a pass), and runs reported separately rather than averaged into a number nobody can check.
The ranking
| # | Tool | ZeroGPT | GPTZero | Free tier | Batch |
|---|---|---|---|---|---|
| 1 | Rephrasy v4 | 9.3 % · human | Likely human | 24 h pass / trial | Dec 2025 + Aug 2026 |
| 2 | humanizer-ai-text.com | 0 % / 27.8 % · human | not run | 100 words/run | Sept 2026 |
| 3 | StayUndetectable | 0 % / 10.6 % · human | not run | 500 words/day | Sept 2026 |
| 4 | Undetectable AI | 7.6 % · human | AI paraphrasing | limited | Dec 2025 |
| 5 | WriteHuman | 12.9 % · human | AI paraphrasing | 250 words | Dec 2025 |
| 6 | StealthWriter | 3.0 % · human | AI paraphrasing | login required | Dec 2025 |
| 7 | Clever AI | 16.5 % · AI | Possible AI paraphrasing | limited | Dec 2025 |
| 8 | HumanizeAI Pro | 36.8 % · AI | AI origin likely | limited | Dec 2025 |
| 9 | QuillBot | 62.1 % · AI | AI paraphrasing | Humanize is Premium | Dec 2025 |
ZeroGPT "human" = under 15 % AI. GPTZero verdict as returned by the tool. September runs show run 1 / run 2.
Rephrasy in detail
Three model generations on GPTZero
January 2026, 100 essays across 50 topics, 600+ detector runs: v2 passed GPTZero on the first try 34 % of the time, v3 67 % (84 % with the creative style). Short texts went from 17.5 % to 67.5 %. v4, August 2026: 9 of 10 fresh documents on GPTZero and on ZeroGPT, semantic similarity 0.925, length 1.05x, about ten seconds per 1,000 words. The v2/v3 and v4 numbers were measured on different test sets (100 essays vs 10 documents).
What a second run does
A 500-word essay written by Claude, scored on GPTZero via the Rephrasy connector: 100 % AI. One pass through v4: 36.4 %, "mixed signals". A second pass on the original: 10.6 %, "reads as human-written". A third: 10.0 %. All inside Claude, without copy-pasting.
Also
ft_clean-v3 for technical text (0.96 meaning retention), custom writing styles trained on your samples, an API from $0.10 per 1,000 words that keeps HTML intact, free re-humanization if a text does not pass. Pricing: Growth $8.25/mo (annual), Business $10/mo with API, Professional $18.33/mo with detector API, lifetime $199, 24-hour pass $12.99.
The free tools
humanizer-ai-text.com
100-word free limit, no signup, Flesch score on every result. Run 1: 0 % on ZeroGPT. Run 2, same input: 27.8 %, still "most likely human written". Restructures sentences rather than swapping synonyms. No detector selection, no API.
StayUndetectable
500 free words a day, no signup, Lite (free) and Ultra (paid). Lite, run 1: 0 % on ZeroGPT. Run 2: 10.6 %, still "human written". Length-faithful, but the rewrite drifts further from the original argument than humanizer-ai-text's. Read it once before you use it.
The rest
- Undetectable AI. 7.6 % on ZeroGPT, "AI paraphrasing" on GPTZero. Frequent user reports of grammar errors. Quick rewrites only.
- WriteHuman. 12.9 % on ZeroGPT, "AI paraphrasing" on GPTZero. In Rephrasy's v4 comparison, 64 % average pass rate across three detectors vs v4's 76 %.
- StealthWriter. 3.0 % on ZeroGPT, the lowest, and still "AI paraphrasing" on GPTZero. Humanize requires an account.
- Clever AI Humanizer. 16.5 % on ZeroGPT, "possible AI paraphrasing" on GPTZero. Turnitin flagged its output as 100 % AI in a separate test.
- HumanizeAI Pro. 36.8 % on ZeroGPT, "AI origin likely" on GPTZero. Failed both.
- QuillBot. 62.1 % on ZeroGPT, "AI paraphrasing" on GPTZero. A paraphraser, not a humanizer; Humanize mode is Premium-only.
Caveats before you quote any of this
- Rephrasy ran these tests. That is why every number has a source you can open, including the runs where a free tool scored lower on ZeroGPT.
- The seven-tool test uses one document per tool. Treat five-point differences between tools as noise.
- Detectors move monthly. Re-check any humanizer number that is older than a quarter.
- GPTZero was not part of the September free-tier batch; those cells are empty rather than passes.
- Humanizing does not make a false claim true or plagiarism original.
How to read "studies" like this one
If a ranking page cannot show you (a) the source text, (b) the humanized output, and (c) a screenshot or API log of the detector verdict, it is a landing page. Affiliate parameters in every tool link are a second tell. Ours: the dataset has all three for every row. Send us your rows and we will add them.
Try it: paste your own text at rephrasy.ai. If it does not pass, re-humanizing is free.