Do AI Humanizers Work? We Tested 12 of Them
Yes, but only the ones that change sentence structure
We get this question constantly. The honest answer is that some AI humanizers work well and most do not.
To find out which ones fall into which camp, we ran a controlled experiment.
Our test setup
- Source: 3,000 words generated by ChatGPT-4o across three formats — an essay, a blog post, and a product description.
- Detectors: Turnitin (institutional), GPTZero (pro), Originality.ai.
- Process: Each tool processed the same text. We submitted the output to all three detectors.
- Runs: Three per tool, to check consistency.
Results summary
| Tool | Turnitin | GPTZero | Originality.ai | Verdict |
|---|---|---|---|---|
| Humanize AI Pro | 2% | 3% | 4% | Works |
| Undetectable AI | 12% | 8% | 9% | Works |
| StealthWriter | 13% | 15% | 22% | Partial |
| BypassGPT | 18% | 21% | 19% | Partial |
| WriteHuman | 26% | 31% | 28% | Inconsistent |
| QuillBot | 89% | 82% | 91% | Does not work |
| Spinbot | 91% | 88% | 94% | Does not work |
Why some work and others do not
The tools that pass detection share one trait: they modify the statistical profile of the text, not just the vocabulary.
AI text has low perplexity (predictable word choices) and low burstiness (uniform sentence length). The working tools introduce variation in both. The failing tools only change words.
Our recommendation
If you need reliable results, use a tool that specifically addresses detector algorithms rather than one that just rewrites phrases. In our testing, Humanize AI Pro was the only free option that consistently scored below 5% across all three detectors.
When humanizers are not enough
No tool can save poorly structured content. If you paste in a bulleted list of ChatGPT talking points, even the best humanizer will produce something that reads awkwardly. Start with a decent AI draft, then humanize.
Dr. Sarah Chen
AI Content Specialist
Ph.D. in Computational Linguistics, Stanford University
10+ years in AI and NLP research