By Aryan Gupta · October 19, 2026
Many AI humanizers claim that they can make ChatGPT writing "100% undetectable." I wanted to find out whether this is true, so I tested five popular free humanizers myself.
In my testing, humanizers were sometimes able to get past regular AI detectors, but they did not make the writing look like a person wrote it. Every humanizer I tested left signs behind, and some of them made the writing worse.
I wrote a paragraph in the style of a typical ChatGPT essay and put it through the free version of each humanizer. Then I checked each result with Optimal, the humanizer checker that I made. I counted a result as caught if it scored 40% or higher.
| Humanizer | Score | Result |
|---|---|---|
| ZeroGPT | 85–95% | Caught every time. Missing words and commas, plus a hyphen character you can't type on a keyboard |
| SuperHumanizer | 95% | Caught every time. Some phrases didn't make sense and the last sentence was cut off |
| Clever AI Humanizer | 75–85% | Caught every time. Weird word choices, and some ideas were different from the original |
| Grammarly (3 full essays) | 75–95% | Caught every time. It mixed British and American spelling and used "carry out" over and over |
| Humanize AI (humanizeai.pro) | 86–100% | Caught every time. It used six different stiff phrases, like "Firstly," "It should be noted that," and "but are not limited to" |
Since part of the score comes from an AI review that can answer differently each time, I ran every sample more than once, and the table shows the range of scores. Every humanizer was caught each time. Grammarly was the hardest to catch because it changes very little, but in longer essays it mixed British and American spelling, which Optimal now checks for. Later, I also tested a basic free humanizer on two short paragraphs, one about volleyball and one about tennis. Optimal missed both of them at first, because that humanizer adds small grammar mistakes and splits sentences into pieces so the writing looks like a younger student wrote it. After I updated Optimal to check for these methods, it scored both paragraphs at 85% or higher. The full results are on the Test Results page.
A humanizer can change the wording of an essay, but it cannot change the content. The original AI essay still has the same structure, the same even coverage of the topic, and the same lack of a real opinion. Because of this, the humanizer can only add changes on top of the essay, and these changes can be found once you know what to look for. The most common ones I saw were:
I explain each of these in more detail in How to Tell if an Essay Was Run Through a Humanizer.
I did not expect how often the humanized versions were worse than the original. In some of them, words were missing and sentences no longer made sense. In others, ideas were replaced with less specific ones, and one humanizer removed the end of the last sentence. A student who turned in some of these versions would likely receive a lower grade even if no one suspected AI use.
I only tested the free versions of these humanizers. Most of them also offer paid versions that may leave fewer signs, and I have not tested those. I also tested a small number of samples, so these results are not final. I plan to test more samples and will update the Test Results page when the numbers change.
Based on my testing, AI humanizers can get past some detectors some of the time, but they still leave enough evidence that a careful teacher or a tool designed to find humanized text can usually notice it. For students, writing the essay yourself may take less effort than fixing the problems a humanizer creates.
To check a piece of writing, you can paste it into Optimal for free.