The 8 Best AI Detectors, Tested and Compared

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AI writing tools are becoming more common every day. But with this rise, it’s getting harder to know what’s written by a human and what’s created by AI. That’s where AI detectors come in. These tools help check if a piece of content was written by a person or generated by AI. If you’re a teacher, student, content creator, or editor, using an AI detector can save time and help you trust your content. In this blog, we’ve tested and compared 8 of the best AI detectors to help you choose the right one.

The Best AI Detectors

Based on our testing, Ahrefs’ AI Detector and Copyleaks worked the best. GPTZero and Originality.ai also gave strong results. On the other hand, Grammarly and Writer did not do well in our tests.

Good news — false positives were not a big problem. Only 2 out of 24 tests marked human-written text as AI by mistake. All tools had the most trouble with content that mixed human and AI writing. (We’ll explain more on this below.)

Ahrefs’ AI Detector

Ahrefs’ AI Detector gave accurate results in most tests. It didn’t wrongly flag any human-written text and could spot AI content clearly. It even showed which AI models were used, like GPT-4o and Meta’s Llama.

Copyleaks

Score: 13/18

Website: https://copyleaks.com/ai-content-detector

Copyleaks had the highest score. It was great at spotting clear AI writing, but sometimes got confused when the content was mixed or not obvious.

GPTZero

Score: 12/18

Website: https://gptzero.me

GPTZero gave steady and trustworthy results. It worked well when AI content was easy to spot. But it wasn’t always confident with mixed or mid-level AI content, which lowered its overall score a bit.

Originality.ai

Score: 12/18

Website: https://originality.ai/ai-checker

Originality.ai did a good job in most tests. It caught strong AI writing well but sometimes thought polished AI text was written by a human.

Scribbr

Score: 10/18

Website: https://www.scribbr.com/ai-detector/

Scribbr gave okay results. It handled clear AI content fine but had problems with more detailed or tricky text. Sometimes, its answers were too careful or didn’t match well with the actual content.

ZeroGPT

Score: 9/18

URL: https://zerogpt.com

ZeroGPT gave mixed results. Sometimes it caught clear AI writing, but often it got confused with content that had just a little AI or was partly human. The tool seemed better at spotting extreme cases and missed the ones in between.

Grammarly

Score: 6/18

URL: https://www.grammarly.com/ai-detector

Grammarly’s free AI tool had trouble giving accurate results. Many times, it gave low-confidence guesses or got the results wrong. It often missed signs of AI writing and didn’t do well with mixed content.

Writer

Score: 4/18

URL: https://writer.com/ai-content-detector/

Writer’s free AI checker scored the lowest in our tests. It often gave wrong results or missed AI writing completely. Even when the text was fully AI-written, the tool gave little helpful feedback.

How AI Detectors Work

All AI detectors work in a similar way. They look for writing patterns that are different from how people usually write.

To do this, the tools need two things:

A lot of samples of both human and AI writing
A model to compare and study those samples

The chart above shows some writing styles that AI tools look for. AI and human writing often look different, and that’s what the tools try to find.

Most detectors today use systems called neural networks. These systems act like a simple brain. They have fake “neurons” that get better through training.

Even small tools can detect AI well, as long as they’re trained with enough examples—at least a few thousand. Many studies show that these tools can get over 80% right. But AI detectors work with probabilities, not clear yes or no answers. That means even the best tools can sometimes be wrong or give false alerts.

The Limits of AI Detectors

Even the top tools, like Ahrefs’ AI detector and Copyleaks, have limits:

If AI writing is changed or edited by a person, the tool may miss it. When we edit AI content, it breaks the patterns the tool looks for.
Free versions or basic tools may not be very accurate. They may also miss new types of AI writing unless updated often.
Some tools don’t work well with less common languages or unusual writing styles. That’s because they are trained mostly on certain types of writing or only one language.
It’s hard to know what counts as AI-written. What if a person writes the content, but AI checks or improves it? What if AI gives the outline, and a person writes the rest? These cases are hard to label, and most tools don’t handle them well.

This matters because most companies don’t publish full AI content. In our research, we found that only 4.04% of online content was 100% written by AI. Most of the time, there’s at least some human editing, which makes detection harder.

Ethical Considerations

Because these tools aren’t perfect, we need to use them carefully. Here are some good tips we follow, with help from the data scientists who built our tool:

Learn about how the tool was trained. Make sure it matches the kind of writing you’re checking.
Test several pieces of writing from the same person. If one article is flagged as AI, check more of their work before making any significant decisions.
Don’t use AI tools to decide things that could affect someone’s job or school work. Use them along with other checks.
Always stay cautious. No tool is perfect, and false alerts can happen.

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Final Thoughts

We used our AI detector to check 900,000 web pages posted in April 2025. We found that 74% of them had some AI-generated content.

AI writing is not going away. That’s why it’s smart to use tools. It helps us understand how AI affects our website and its performance.

FAQs

AI detectors are software tools designed to analyze text patterns and determine the likelihood of AI-generated content. They compare writing styles against known human and AI models to flag potential machine-written text.

AI detection accuracy varies by tool and model. Leading detectors can reach 80%+ accuracy, but results are probabilistic rather than definitive and often struggle with nuanced or edited content.

Based on comprehensive testing, Ahrefs’ AI Detector and Copyleaks performed best, consistently identifying AI-generated text while minimizing false positives compared to other tools.

Mixed content disrupts predictable AI patterns. When humans heavily edit AI drafts, natural variability is introduced, making AI writing detection significantly more difficult.

AI detectors rely on neural networks trained on large datasets of human and AI text. They analyze structure, predictability (burstiness), and complexity to generate a probability score.

Key limitations include difficulty detecting heavily edited AI text, reduced accuracy for non-English languages, and constraints in free versions. These tools suggest probability, not definitive authorship.

Heavily edited AI content is difficult to detect, as human revisions reduce algorithmic signals. However, subtle edits may still be identified by advanced tools like Copyleaks.

False positives can occur, though accuracy is improving. In testing, only 2 out of 24 human-written texts were incorrectly flagged, highlighting the need for human review in critical decisions.

Educators, editors, and digital marketers benefit most from AI writing detection tools to verify authenticity, uphold integrity standards, and ensure content quality.

Because AI detection is not 100% accurate, using it as sole evidence for punishment is ethically risky. These tools should be treated as screening aids, not definitive proof.