9 Best AI Detectors Tested and Reviewed

Introduction

AI writing tools like ChatGPT, Claude, and Gemini have revolutionized the way people write. But with this revolution comes a growing demand for AI detection tools, software that determines whether a piece of text was written by a human or AI.

In 2025, educators, employers, publishers, and businesses are relying on AI detectors to verify the authenticity of written content. But are these tools reliable? Which ones work best? And is it even possible to bypass them?

We tested and reviewed the 9 best AI detectors on the market:

GPTZero, ZeroGPT, Turnitin, Copyleaks, TwainGPT, QuillBot, Grammarly, Scribbr, and Originality AI.

This guide will break down:

• How AI detectors work
• Which tools are most accurate
• How they perform on GPT-5 content
• Whether they can be bypassed
• Which one is best for your needs

Let’s dive in.

1. How Do AI Detectors Work?

AI detectors analyze patterns in text to determine whether it was written by a human or generated by AI. They look for specific linguistic fingerprints left by large language models.

Common detection signals include:

• Perplexity: How predictable the words in a sentence are
• Burstiness: Variation in sentence length and structure
• Repetition: LLMs often repeat ideas in similar formats

Different tools use different techniques, but nearly all rely on statistical analysis of the text — comparing it to known AI outputs to make a decision.

The issue? Even human writers can sometimes “look” like AI based on how formulaic their writing is, and ChatGPT is getting more human-sounding every month.

2. The 9 Best AI Detectors in 2025

Here are the most widely used and trusted AI detectors this year:

🥇 GPTZero

Considered the most popular AI detector. Offers sentence-by-sentence breakdowns and overall probability scores. Excellent interface and reporting, widely used in education.

🥈 Turnitin

The gold standard in schools and universities. Difficult to bypass and widely feared by students. Provides originality + AI analysis in one report.

🥉 ZeroGPT

Simple to use and often accurate, but sometimes misclassifies well-edited AI content. Free, no downtime, and fast results.

✅ Copyleaks

Used by businesses and schools. High accuracy and low false-positive rates. Strong enterprise features.

✅ TwainGPT

Although best known as an AI humanizer, TwainGPT includes a reliable AI detector to scan your content post-rewrite.

✅ QuillBot

QuillBot’s AI detector is built right into its writing suite, making it easy to access. Its results are reliable and continue to improve with each update.

✅ Scribbr

Scribbr’s AI detector is a QuillBot embed. It runs on the exact same engine, so the accuracy, weaknesses, and results are identical.

✅ Grammarly

A recent addition to their platform, still being refined. Decent accuracy but useful if you already use Grammarly Premium.

✅ Originality AI

Popular among web publishers and SEO writers. Offers both AI detection and plagiarism checking.

3. GPT-5 Detection Results

We tested a variety of AI detectors using GPT-5-generated content. The goal was to see whether the top tools could reliably flag advanced AI output.

Here’s what we found:

• Turnitin, GPTZero, ZeroGPT, TwainGPT, and Copyleaks performed the best.
• QuillBot and Scribbr did well in most cases.
• Grammarly and Originality.ai showed weaker detection

Most importantly, none of them were perfect — especially when the writing was humanized using TwainGPT's AI humanizer.

4. Can AI Detectors Be Bypassed?

Yes, AI detectors can be bypassed, even in 2025.

A common myth is that simple paraphrasing can bypass AI detection. In reality, tools like Turnitin and GPTZero are trained to flag that kind of robotic rewriting.

To bypass AI detectors, your text needs to be restructured, reworded, and stripped of AI patterns — something that AI humanizers specialize in.

One tool stands out in this category: TwainGPT.

Unlike AI paraphrasers, TwainGPT was built specifically to bypass AI detection.

5. Real-World Examples of Bypassing Detection

To test this, we ran AI-generated text through popular detectors, then humanized that text with TwainGPT, and ran it again.

Before humanizing:

• GPTZero: 100% AI
• Turnitin: 100% AI
• ZeroGPT: 98% AI
• Copyleaks: 96% AI

After TwainGPT:

• GPTZero: 1% AI
• Turnitin: 0% AI
• ZeroGPT: 1% AI
• Copyleaks: 0% AI

You can see the real screenshots below from our testing:

6. Which AI Detector Should You Use?

Here’s a quick breakdown:

Based on our testing, GPTZero, Copyleaks, ZeroGPT, TwainGPT, and Turnitin are the best AI detectors.

Originality.ai, Scribbr, Grammarly, and QuillBot are also reliable.

Final Verdict: AI Detectors Are Evolving, But So Are AI Humanizers

AI detectors are getting more advanced every day. But they’re not perfect, and they’re definitely not unbeatable.

Writers using AI are choosing TwainGPT to humanize their text to bypass AI detection.

If you're serious about bypassing AI detectors in school, publishing, or business:

👉 Try TwainGPT Now — the best AI humanizer to bypass AI detectors today.