Free AI Detector
Check if text was written by ChatGPT, Claude, Gemini, or another AI model. Get an instant AI-probability score no account needed.
Check Text for AI →Paste any text and click Detect AI
How the AI detector works
Analyze perplexity
Perplexity measures how predictable each word choice is. AI language models are trained to choose the most probable next word making their output very low-perplexity. The detector measures this signal and compares it against human writing baselines.
Measure burstiness
Burstiness measures how much sentence lengths vary. Human writing bursts short sentences, then long ones, then medium, with no pattern. AI writing is uniformly structured. This is one of the most reliable detection signals because it's structural, not vocabulary-based.
Return AI probability score
The detector combines perplexity and burstiness signals into an overall AI-probability score (0–100%). Scores above 70% indicate likely AI-generated text. Scores below 30% indicate likely human-written text. Scores in between are ambiguous.
What AI sources it detects
TextHumanizer's detector identifies text from any large language model because it targets the statistical properties all LLMs share, not any specific model's fingerprint.
Who uses the AI detector
Teachers and professors
Check student submissions for AI-generated content before grading or flagging.
Content editors
Verify that freelance-submitted content wasn't AI-generated without disclosure.
Publishers
Screen inbound pitches and guest posts for AI-generated content at scale.
Writers checking their own work
Verify that your own writing doesn't accidentally score as AI-generated before submitting.
Students
Check that your legitimate work won't be incorrectly flagged by your institution's detection tools.
HR and recruitment
Screen job application essays and cover letters for AI-generated content.
Text scored as AI? Humanize it.
If your text scored high for AI probability, TextHumanizer can rewrite it to exhibit human-typical statistical properties raising perplexity and burstiness until the score drops. The meaning stays intact.
Humanize This Text →Frequently asked questions
How does the TextHumanizer AI detector work?
TextHumanizer's AI detector analyzes text for the statistical signatures of AI-generated content primarily perplexity (how predictable each word choice is) and burstiness (how uniform sentence lengths are). AI models consistently produce low-perplexity, low-burstiness text. The detector scores these signals and returns an AI-probability percentage.
Is the AI detector free?
Yes. TextHumanizer's AI detector is completely free to use with no signup or credit card required. Paste your text and get an AI score instantly.
What AI models can the detector identify?
The detector identifies text generated by any major AI writing model including ChatGPT (GPT-4, GPT-3.5), Claude, Gemini, Llama, Mistral, Copilot, and other large language models. It targets the statistical properties shared by all LLM outputs, not any specific model.
How accurate is the AI detector?
TextHumanizer's detector is highly accurate on clearly AI-generated text. Like all AI detectors, it can produce false positives flagging human writing that happens to be very uniform or formal. Short texts (under 100 words) are less reliably scored due to insufficient statistical sample size.
If my text scores as AI-generated, can I fix it?
Yes. Use TextHumanizer's humanization tool to rewrite the text with higher perplexity and burstiness. Paste your text into the humanizer, click Humanize, and then re-check with the detector to verify the score dropped.