Undetectable AI vs. Isgen: Can This AI Detector Beat The Best AI Humanizer?

The race between AI and the tools designed to detect it is never-ending. Just when you think you've found the AI detector, a new piece of tech comes along that's designed to slip right past your defenses.

But what happens when you pit Undetectable AI against an up-and-coming AI detection tool? That's exactly what I set out to discover by testing Isgen, a free platform that claims a staggering 96.4% accuracy rate in identifying AI-generated text across 80+ languages. 

Could this little-known detector stand up to the might of Undetectable AI, or would it crumble under the pressure just like so many others?

2026 update: I’m keeping the original test order and screenshots intact. Use this as a point-in-time comparison, because both Isgen and Undetectable AI can change their scoring and rewriting behavior over time.

What is Undetectable AI?

Most AI paraphrasers try to make your writing cleaner. Undetectable AI is different because it is built around humanizing text and checking how that text looks to common AI detectors.

By inputting a piece of text into Undetectable AI and pressing “Humanize,” you can get a rewritten version that often looks less machine-like to detectors. You can also change readability, use case, and balance settings to better match the intent of the original text, but the output still needs human review.

You can read more about this tool in our complete review here.

What is Isgen?

AI detection tools are a dime a dozen nowadays, but Isgen promises to be the most precise free AI detector. It claims that it’s able to detect AI content written in 80+ different languages with an accuracy of 96.4%. But does that reflect reality?

Undetectable AI vs. Isgen: Accuracy Test

We’ve already tested Undetectable AI before against the most popular AI detection tools and it won pretty convincingly. Will Isgen be one of the few that can stand against it? Let’s test it against Undetectable AI by generating content from three of the most popular LLMs today: Claude, ChatGPT, and Gemini.

Using Claude

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 0%

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 0%

Isgen AI: Successfully classified Undetectable AI’s text as AI-generated.
AI Likelihood Score: 100%

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 0%

Using ChatGPT

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 0%

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 0%

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 15%

Isgen AI: Successfully classified Undetectable AI’s text as AI-generated.
AI Likelihood Score: 100%

Using Gemini

Isgen AI: Successfully classified Undetectable AI’s text as AI-generated.
AI Likelihood Score: 100%

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 20%

Isgen AI: Successfully classified Undetectable AI’s text as AI-generated.
AI Likelihood Score: 84%

Isgen AI: Unsuccessfully classified Undetectable AI’s text as human-written.
AI Likelihood Score: 0%

For another humanizer matchup, read our GPTHuman vs Undetectable AI test.

For broader detector context, compare this with our Undetectable AI detector self-test and our guide to free ChatGPT checkers.

The Final Tally + Thoughts

You might see this score and assume that Isgen AI isn’t worth your time — I’d argue the opposite. Here’s why:

We’ve tested some of the most popular AI detection tools against Undetectable AI, and their average AI likelihood scores are:

• Winston AI: 48.88%
• GPTZero: 29.7%
• ZeroGPT: 0%
• Writer.com: 0.22%
• BrandWell: 0%
• Hive Moderation: 9.58%

I had low expectations of Isgen, especially since it was less popular than its competitors, but it proved me wrong in this test. At 34.92%, it was one of the stronger free detectors we had tested against Undetectable AI at the time, behind Winston, which is a paid service.

So, What Now?

At the end of the day, the battle between Isgen and Undetectable AI is a good example of how quickly this space changes. A detector can look strong in one test set, then struggle when humanizers, writing models, or detector thresholds change.

But you know what they say — you can't keep a good detector down. And Isgen has proven that it's got the chops to hang with the big dogs, even if it's not a household name… yet.

Of course, no detector is perfect, and I'm sure Undetectable AI will continue to innovate and find new ways to evade detection, especially since false positives are still a worry in AI detection. But for now, Isgen stands out as one of the most capable free AI detectors on the market. 

If you're looking for a free detector to test against humanized AI writing, Isgen is worth trying. If you’re more worried about false-positive AI detection, Undetectable AI is still useful as a detector-and-humanizer workflow, but you should pair it with manual editing and at least one other detector.