Free AI Detector
Check if text was written by ChatGPT or another AI. Get an AI score and see which sentences read as AI. 800 words free, no sign-up.
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What is an AI detector?
An AI detector estimates whether a piece of text was written by a person or produced by an AI model like ChatGPT. HumanizerPRO's free AI detector gives your text an overall AI score and scores each sentence, so you can see exactly which lines read as AI instead of guessing from a single number.
AI writing tends to be smooth and predictable: similar sentence lengths, safe word choices and the same transitions again and again. That's what the detector looks for. It can't prove who wrote something, but it points out the parts that sound like a machine wrote them, which is what you need to fix a text or to ask better questions about it.
- Free
- 800 words per check, no sign-up
- Paid plans
- Up to 5,000 words per check
- Results
- Overall AI score plus sentence-by-sentence highlights
- History
- Your last 30 checks, saved only in your browser
How the AI detector works
Click a step to see what happens to your text.
How to check if text is AI-generated
It only takes a few seconds to check a text. Here's how to do it in HumanizerPRO.
- 1
Paste your text
Paste or type at least 50 characters, or upload a file. Without an account you can check up to 800 words at a time.
- 2
Click Detect AI
Or press Ctrl+Enter. Most checks finish in a few seconds.
- 3
Review the highlights
Check the overall score, then filter to the sentences marked as AI to see what triggered it.
- 4
Fix and check again
Rewrite flagged sentences in your own words, or click Humanize this text to open them in our AI humanizer, then run the check again.
How accurate is it? We tested it
In October 2026, the HumanizerPRO team ran 60 texts written by ChatGPT (GPT-4.1) and 30 texts written by people through the AI detector. Blog posts, essays, articles, emails and product descriptions were among the 60 ChatGPT texts. The human texts came from an open research dataset.
ChatGPT texts flagged as AI or mixed. None was rated likely human.
Average AI score on the ChatGPT texts (57 of 60 rated likely AI).
Human texts rated likely human. The other 7 were rated mixed, and none was rated likely AI.
No AI detector is 100% accurate, ours included. Read more about why in are AI detectors accurate?
How to read your AI score
The overall score is an estimate of how much of your text appears to be AI-written, not how likely it is that someone cheated. The sentence highlights matter more than the number: they show you where to look.
Under 30%: Likely human-written
Few or no sentences look AI-generated.
30% to 69%: Mixed
Parts look AI-generated. Common for AI drafts that were edited, and for formal human writing.
70% and over: Likely AI-generated
Most sentences match AI writing patterns. Check the highlighted lines first.
What you get with this AI checker
Everything you need to find AI-sounding writing and fix it, in one place.
Sentence-by-sentence highlights
Every sentence is colour-coded in line, so you can see what's contributing to the score.
Filter by result
Show only AI or only human sentences, and click one to jump to it in your text.
One click to humanize
Send flagged text to our free AI humanizer and check it again.
Check history
Your last 30 checks are stored in your browser, with a search box. Nothing is stored in an account.
Paste, type or upload
Upload .txt and .md files, or try the sample text to get an idea of how it works.
Free, no sign-up
Check up to 800 words at a time for free. Paid plans raise the limit to 5,000 words.
What an AI detector can't tell you
AI detectors look at patterns, not intent. Formal, simple or heavily edited human writing can score as AI, and AI text reworked by a person can pass for human. In our test, 7 of 30 human texts were rated mixed.
Never treat one score as proof. Teachers and editors should look at drafts, sources and the writer's own explanation as well. If your own writing was flagged, read what to do if you're falsely accused of using AI, and see how to tell if text is AI-generated for the signs people use.
Who uses this AI detector
Students
Check a draft before you submit it, and find the sentences that may get flagged.
Teachers
Get an early signal on an essay, then discuss the highlighted sections with the student.
Writers and bloggers
Make sure AI-assisted drafts read like you before you publish.
Editors and agencies
Screen freelance and client content quickly, sentence by sentence.
More free tools
Frequently asked questions
Is this AI detector free?
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Yes. You can check up to 800 words at a time for free, with no account and no sign-up. Paid plans allow up to 5,000 words per check.
How accurate is the AI detector?
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In HumanizerPRO's October 2026 test, all 60 ChatGPT texts were rated AI or mixed (57 of them likely AI), and 23 of 30 human texts were rated likely human. No AI detector is 100% accurate, so treat the score as one signal, not proof.
Can it detect ChatGPT?
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Yes. In our test, ChatGPT text was flagged reliably: the average AI score was 90%, and none of the 60 ChatGPT texts was rated likely human. It checks text from other AI writing tools the same way.
Why was my own writing flagged as AI?
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Formal, simple or very polished writing can look predictable, which is what detectors look for. In our test, 7 of 30 human texts were rated mixed. Check which sentences were highlighted, and see what to do if you're falsely accused of using AI.
What does the AI percentage mean?
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It's an estimate of how much of your text reads as if it was written by AI. Under 30% means likely human, 30% to 69% means mixed, and 70% or more means likely AI. It isn't the probability that someone used AI.
Does it check sentence by sentence?
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Yes. Every sentence is highlighted as likely AI, possibly AI or likely human inside your text, and you can filter the results to see only the AI sentences.
Is my text saved?
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Your check history is stored only in your own browser, and you can delete it whenever you want. HumanizerPRO doesn't save the text you check to an account.
How do I make AI text sound human?
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Rewrite the highlighted sentences in your own words, or use HumanizerPRO's free AI humanizer. To write new content that sounds human from the start, try the Human AI Writer.