Multi-model coverage
Trained against output from GPT-4, GPT-3.5, Claude 3, Gemini, Llama and a dozen open-source models. Detection holds up across every major LLM in the wild today.
AI Content Detector
Tell what's AI. In one click.
AI Checker is the fastest way to spot writing from ChatGPT, GPT-4, Claude, Gemini and other large language models. Paste any text — get an instant AI probability score with sentence-level highlights.
2,481,902 texts analyzed this week
Trusted by educators and editorial teams
Westbrook UniversityDaily JournalAtlas PressLumen SchoolsLedger MediaNorthbridge College
Live demo
See AI detection in action.
Paste any passage of text to see an instant AI probability score, with sentence-level highlights so you can act on the result.
ai-checker.co / detectPowered by AI Checker
Artificial intelligence has fundamentally transformed the landscape of modern content creation. Through sophisticated language models, machines can now produce coherent, contextually relevant text that closely mirrors human writing patterns. This technological advancement raises important questions about authenticity and attribution.
AI probability
94%likely AI
- Detected fingerprints: GPT-4, Claude 3
- 2 of 3 sentences flagged as AI
- Perplexity: 18.4 (low — typical of LLMs)
- Burstiness: 0.31 (uniform — AI-like)
Capabilities
Everything you need to spot AI writing.
Built for editors, educators, recruiters, and developers who need a detector they can actually trust.
Sentence-level highlights
See exactly which sentences raised the AI score, color-coded so you can review or rewrite only the parts that matter.
Paraphrase resistant
Multiple complementary signals catch lightly humanized, AI-rewritten, or paraphrased text that fools simpler detectors.
Privacy-first
Your text is processed in memory and never used to train models. Opt out of all logging from a single toggle.
Public REST API
A clean REST API for LMS, plagiarism platforms, content marketplaces, and editorial tools — sentence breakdown included.
Free to start
Run quick checks for free — no signup, no credit card. Upgrade only when you need bulk analysis or team features.
Compare
AI Checker vs. the alternatives.
How AI Checker stacks up against GPTZero, ZeroGPT, and Originality.ai on the features that actually matter.
| Feature | AI CheckerUs | GPTZero | ZeroGPT | Originality.ai |
|---|---|---|---|---|
| Multi-model coverage (GPT, Claude, Gemini) | — | |||
| Sentence-level breakdown | — | |||
| Free tier without char-limit traps | — | — | ||
| Public REST API | — | |||
| Paraphrase resistance | partial | — | ||
| On-device privacy mode | — | — | — | |
| No-signup access | — | — |
How it works
Three steps. No account required.
Want a deeper technical breakdown? Read how AI content detection works.
Paste your text
Drop in any text — an email, an essay, a blog post, a code review. Up to 10,000 characters on the free tier.
Run the analysis
AI Checker scans your text against signatures from every major language model and computes a probability score.
Review the score
Get an overall AI percentage plus a sentence-by-sentence breakdown so you know exactly what to look at.
Use cases
Built for teams that work with text.
Wherever AI-generated content shows up, AI Checker fits in.
Educators & academia
Spot AI-written essays, lab reports, and admissions material before they land on your desk.
Publishers & editors
Verify freelance submissions, ghostwritten drafts, and ensure original human voice in every piece.
Recruiters & HR
Catch AI-generated cover letters, take-home assignments, and questionnaire answers in your hiring funnel.
SEO & content teams
Audit agency deliverables, validate human-first content for Google's E-E-A-T guidelines, and stay penalty-safe.
Legal & compliance
Review contracts, briefs, and depositions for AI-assisted drafting where source attribution matters.
Government & policy
Validate citizen submissions, public comments, and policy responses for AI-generated astroturfing.
Understanding AI text detection
What you should know before trusting any AI score.
How AI detectors actually work
Modern AI content detectors combine three signals — each defined below.
- Perplexity
- A measure of how predictable a sequence of text is to a reference language model. AI-generated text is typically low-perplexity because each token was chosen to maximize probability; human text is higher-perplexity due to unusual word combinations and tangents.
- Burstiness
- Variation in sentence length, structure, and rhythm across a passage. Human writing is bursty — long sentences mixed with short — while AI tends toward uniform mid-length sentences. A strong signal because it is hard to evade without rewriting.
- Lexical fingerprinting
- Comparison of a passage against statistical signatures of known LLMs (GPT-4, Claude, Gemini, etc.) to identify the most likely source model. Each model leaves subtle preferences in word choice, hedging phrases, and parenthetical structure.
Why no detector is 100% accurate
Every detector — including ours — has false positives and false negatives. Heavy paraphrasing, “humanizer” tools, and hybrid human-AI editing can lower a score without zeroing it out. Conversely, certain styles of human writing (highly formal, technical, templated) can occasionally read as AI to a detector. The honest numbers: state-of-the-art detectors hit 95–98% on unedited AI text and roughly 1–2% false positive rate on human writing. Any tool claiming 100% accuracy is overselling.
Best practices for using detection results
Treat any AI score as one signal in a human review process — never the final verdict. Read the sentence-level breakdown: if a single paragraph triggers the score and the rest reads like the author, that's very different from a uniformly high reading. For educators, pair the score with classroom context, version history, and a conversation with the student. For editors and recruiters, use the score to decide where to focus your review, not whether to reject someone outright. The full technical primer is in our guide to how AI content detection works.
Frequently asked
Questions and honest answers.
How does AI Checker detect AI-generated content?
AI Checker analyzes linguistic patterns, perplexity, burstiness, and statistical fingerprints that large language models leave behind. Each sentence is scored against signatures from ChatGPT, GPT-4, Claude, Gemini, Llama, and other major models, then combined into an overall AI probability score.
Is AI Checker free to use?
Yes. AI Checker offers a free tier that lets you analyze text without an account. Higher-volume usage, API access, and team features are available on paid plans, but core detection is always free.
Can it detect ChatGPT, GPT-4, Claude, and Gemini?
Yes. AI Checker is trained against output from every major large language model, including OpenAI's GPT-3.5 and GPT-4, Anthropic's Claude family, Google's Gemini, Meta's Llama, and several open-source models. New models are added as they are released.
How accurate is AI Checker?
On standard academic and journalistic benchmarks, AI Checker reaches over 98% accuracy on unedited AI text and over 90% on lightly edited or paraphrased content. No detector is perfect — we always recommend treating the score as a strong signal, not a verdict.
Does it still work if the AI text has been paraphrased?
Yes. AI Checker uses multiple complementary signals so that even paraphrased, humanized, or AI-rewritten text usually still trips at least one detector. Heavily edited content lowers confidence, and the result will reflect that.
What languages are supported?
AI Checker supports English with the highest accuracy. It also works on Spanish, French, German, Italian, Portuguese, Turkish, and over a dozen other languages, with steadily improving detection quality.
Is my data private?
Yes. Text submitted to AI Checker is processed in memory and is not used to train models. We do not sell or share your content, and you can opt out of all logging from the privacy settings.
Can I integrate AI Checker via API?
Yes. A REST API is available for plagiarism platforms, learning management systems, content marketplaces, and editorial tools. The API returns a sentence-level breakdown in addition to the overall score.
Will AI Checker work on student essays?
Yes — student essays are one of the most common workloads on AI Checker. The detector handles long-form academic prose, lab reports, and admissions essays with equal accuracy. Paste up to 10,000 characters at once.
Can teachers use this for academic integrity?
Absolutely. AI Checker is widely used by educators in K-12 and higher education for academic integrity workflows. We always recommend treating any AI score as one input among many — pair it with classroom context, version history, and conversation with the student before drawing a conclusion.
Does it integrate with Turnitin or Canvas?
Direct integrations with Turnitin and Canvas are on the roadmap. In the meantime, the AI Checker REST API can be wired into LMS plugins, browser extensions, or grading workflows — most teams ship a working integration in under a day.
What's the difference between AI Checker and GPTZero?
Both tools target the same problem, but AI Checker covers more models out of the box (Claude and Gemini in addition to GPT), provides a clearer sentence-level breakdown, and exposes a free public API. We also keep the free tier genuinely useful — no daily char limit traps.
Stop guessing. Start checking.
Run your first AI content check in under 10 seconds. Free forever for casual use.