Undetectable AI vs. Scribbr: Which One Detects AI Writing More Accurately?

AI detectors have gotten loud lately. Every week there’s a new tool promising “near-perfect accuracy,” a dashboard full of colored bars, and a shiny demo that somehow always looks more impressive than what you get in real use. 

But here’s the reality: most people don’t need another sales pitch — they need a detector that actually understands modern AI writing, especially now that tools like ChatGPT, Claude, and humanizers have made things harder to catch.

That’s why the matchup between Undetectable AI and Scribbr’s AI Detector is well overdue.

Two detectors. Two different philosophies. One question: which one actually performs better when the writing isn’t easy to judge?

What is Undetectable AI?

Undetectable AI made waves as an AI humanizer: a tool that can transform any AI-written content into something more human. However, they’ve built tons of new features on top of that they’ve created a full-blown AI writing assistant.

One of those is their AI detection tool. This detector leans more toward technical accuracy, readability scoring, and assessing how “AI-like” a piece of text feels based on patterns. It’s simple, straightforward, and tuned for the modern AI-writing landscape — meaning it’s built to detect newer model outputs, not just GPT–like text.

What is Scribbr?

Scribbr’s detector is built for academics — not marketers, not bloggers, not content writers.

Students make up the bulk of their user base, and you can feel it.

The tool is meant to:

• Scan essays, research papers, and assignments
• Highlight AI-written segments in a clean, report-style layout
• Give professors or students a quick way to evaluate authenticity
• Provide a “confidence level” that reads more like a Turnitin-style checkup

Unlike UD, Scribbr’s vibe is slower, more methodical, and very “academic tool”—the kind of interface that looks like it could be linked inside a university portal.

It excels at:

• Sentence-level highlighting
• Showing transparency (why it thinks something is AI)
• Providing downloadable reports
• Helping students avoid accidental plagiarism or AI overreliance

Undetectable AI vs. Scribbr: AI Detection

Test #1

AI-generated Text:

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 99%

Scribbr: Incorrectly identified text as human-written.
AI Likelihood Score: 0%

Test #2

AI-generated Text:

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 99%

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 100%

Test #3

AI-generated Text:

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 91%

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 100%

Test #4

AI-generated Text:

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 99%

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 62%

Test #5

AI-generated Text:

Undetectable AI: Correctly identified text as AI-generated.
AI Likelihood Score: 99%

Undetectable AI: Detector confused!
AI Likelihood Score: 53%

Average Score

The Bottom Line

After running both tools through the same batch of AI-written and human-written samples, the gap became impossible to ignore: Undetectable AI’s detector hit 97.4% accuracy, while Scribbr landed at 63%.

And honestly, that tracks.

Undetectable AI has always been built around understanding the texture of AI writing — the pacing, the cadence, the little tells that newer models still struggle to mask. Their whole ecosystem revolves around spotting (or hiding) those patterns, so the detector feels sharper, faster, and way more in tune with how modern AI actually writes.

Scribbr, on the other hand, is still good — especially in an academic setting. It highlights sentences cleanly, it gives structured reports, and it’s built for classrooms, not high-speed content analysis. But when it comes to raw accuracy, especially with newer LLM outputs, it just can’t keep up with UD’s more evolved detection style.

Both tools still have their lanes, but based on performance alone, Undetectable AI is the clear winner in this matchup.