AI Detector
The free AI detector trusted by teachers, editors, and content teams. Detect ChatGPT, GPT-4, Claude, and Gemini text with sentence-level accuracy.
No signup. 95%+ accuracy. Sentence-level highlighting.
What is an AI detector?
An AI detector is a tool that estimates the probability that a piece of text was written by a large language model — ChatGPT, GPT-4, Claude, Gemini, or any other current AI. It reads the input, extracts statistical features, and runs them through a classifier trained on millions of human and AI writing samples. The output is a confidence score, usually with sentence-level highlighting so you can see exactly which parts look machine-generated.
Good AI detectors are model-agnostic. The fingerprint of AI-generated text is shaped by the transformer architecture itself, not by any single model — so a detector trained well on GPT-4 output usually generalizes to Claude and Gemini too.
How AI detection actually works
The underlying signals fall into three categories:
- Token-level predictability. AI models tend to pick the next word that a language model would predict — by definition. Human writers make surprising choices more often. Detectors measure the perplexity and burstiness of the text.
- Stylistic patterns. AI output has recognizable verbal tics — overuse of certain transition phrases ("moreover", "in conclusion"), balanced sentence lengths, neutral register, and hedging language ("it's important to note that").
- Structural fingerprints. AI tends toward uniform paragraph lengths and predictable argument structure (claim → reasoning → example → conclusion), even where a human would vary.
A modern detector like aidetectors.io combines all three into an ensemble classifier and trains continuously against fresh AI output as new models ship.
AI detector accuracy in 2026
| Content type | Typical accuracy | Notes |
|---|---|---|
| Unedited GPT-4 output | 94-97% | Easiest to catch |
| Unedited Claude output | 92-95% | Slightly more human-like prose |
| Unedited Gemini output | 90-94% | Varies by prompt style |
| Lightly edited AI | 75-88% | Sentence-level mixing |
| Paraphrased AI | 60-80% | Detection harder but still possible |
| Heavily humanized AI | 40-65% | Best workflow: detect → humanize → re-detect |
Who uses AI detectors
- Teachers and professors grading essays, theses, and short-answer responses
- Editors and content managers verifying freelance submissions are human-written
- SEO teams auditing content before publishing to avoid Google's spam-policy risk
- Recruiters screening cover letters and writing samples
- Researchers studying AI prevalence in academic work
- Writers checking their own AI-assisted drafts to ensure they read as human
What makes the best AI detector in 2026
The criteria that actually matter:
- Multi-model detection. Must catch ChatGPT, Claude, Gemini, Llama, and emerging models — not just GPT-3.5 from 2023.
- Low false-positive rate. A detector that flags real human writing as AI is worse than no detector. Target: under 5%.
- Sentence-level highlighting. Whole-document scores hide mixed content. You need to see which sentences are suspicious.
- No paywall on basic use. Free scans should give you the full result, not a redacted teaser.
- Transparent methodology. Look for tools that publish their evaluation approach.
For a head-to-head comparison of free options, see our 2026 free AI detector benchmark.
How to use our AI detector
- Go to the AI detector
- Paste your text into the input box (up to 5,000 characters per scan)
- Click "Detect"
- Review the overall score and sentence-level highlights
- If you need to humanize flagged sections, use our humanizer
AI detector vs plagiarism checker — what's the difference?
A plagiarism checker compares text against a database of existing content to find verbatim or near-verbatim matches. It tells you whether text was copied. An AI detector analyzes the text itself for statistical signs of machine generation. It tells you whether text was generated, regardless of whether the content is original.
They solve different problems. AI-generated text is rarely plagiarized — the AI made it up — so a plagiarism checker will pass it. You need a real AI detector.
Frequently asked questions
What is an AI detector?
An AI detector is a tool that analyzes text to estimate the probability that it was written by an AI model like ChatGPT, GPT-4, Claude, or Gemini. Modern detectors use multi-model classifiers trained on millions of human and AI samples to identify the statistical fingerprints of machine-generated text.
How accurate is AI detection in 2026?
The best AI detectors achieve 90-96% accuracy on unedited AI output. Accuracy drops on heavily edited or paraphrased content. Always verify with multiple samples and consider context — no detector is 100% accurate.
Is this AI detector free?
Yes. You can run AI detection scans on aidetectors.io without an account. Free scans include sentence-level highlighting and multi-model detection — the same features paid tools charge for.
Can AI detectors detect ChatGPT, Claude, and Gemini?
Yes. A good AI detector is model-agnostic — it identifies AI-written text regardless of which model produced it. We test against GPT-4o, Claude Sonnet, Gemini Pro, and other current models.
Do AI detectors give false positives?
They can. Human-written text with very regular structure (technical writing, simple sentences, non-native English) is most likely to be flagged incorrectly. Our false-positive rate in 2026 benchmarks is around 3%.
Can I bypass an AI detector?
Heavily-edited AI text, or text rewritten with a purpose-built humanizer, is harder for detectors to catch. But generic paraphrasing tools rarely fool modern detectors. See our humanize tool for more.