The best AI detection tools, and what their scores can and cannot tell you

AI detectors estimate how likely it is that a piece of text was written by a language model. Teachers use them on essays, editors on submitted articles, and recruiters on cover letters. This page compares five AI detection tools on price and the accuracy each vendor claims, as of October 2026, and sets those claims next to what independent researchers found. Read the second part before you act on any score.

What AI detectors are for

A detector is a screening tool. It flags text that shares statistical patterns with output from AI chatbots, so a person can look closer. It cannot see how the text was produced. Grammarly states this plainly in its own FAQ: detectors can indicate characteristics of human or AI writing, but they cannot definitively conclude whether AI was used, and they should be one part of a holistic approach.

Good uses: an editor triaging a pile of freelance submissions, a teacher deciding which drafts to discuss with a student, a publisher checking its own AI policy is followed. Poor uses: grading, discipline or rejection based on a percentage alone.

What the research says about accuracy

Vendors publish accuracy figures from their own tests. Independent studies are more cautious:

• Non-native English writers get flagged more. A Stanford-led study (Liang et al., 2023) found several widely used GPT detectors consistently misclassified writing by non-native English speakers as AI-generated, while native writing was identified correctly. The authors cautioned against using detectors in evaluative or educational settings.
• Tools vary widely. A 2023 study by Weber-Wulff and 15 co-authors tested 12 public tools and two commercial systems, including Turnitin, and concluded the tools were neither accurate nor reliable, with a bias toward labeling text as human-written.
• Small error rates add up at scale. When Vanderbilt University disabled Turnitin's AI detector in August 2023, it noted Turnitin's launch claim of a 1% false positive rate. Applied to the 75,000 papers Vanderbilt submitted in 2022, that would mean around 750 papers wrongly flagged.

Detectors have improved since 2023, and several vendors now publish third-party evaluations. The structural point holds: a false positive accuses a real person, so the cost of an error is high even when the rate is low.

How the picks were chosen

This page is part of our AI tools catalog. We kept detectors that publish their pricing or are free, describe how their scores should be read, and are widely used in education or publishing. We list each vendor's own accuracy claim and say whose test it comes from. We did not run our own accuracy test.

The five detectors at a glance

1. GPTZero

Best for: teachers who want scans inside Google Docs and the classroom · Price: Premium $12.99/month, Professional $24.99/month, both billed annually (as of Oct 2026) · Free plan: yes

GPTZero says it is trusted by more than 10 million teachers and students and is an official AI detector partner of the American Federation of Teachers. The free scanner takes up to 10,000 characters; longer scans need a free account. Premium covers up to 300,000 words a month with multilingual detection and downloadable reports. Professional adds up to 10 million overage words, batch scans of up to 250 files, page-by-page scanning of long documents and LMS integration. GPTZero also offers a writing replay that shows how a document was typed, which gives a teacher more to go on than a percentage.

Claims and caveats: the homepage advertises 99% accuracy. GPTZero says it retrains its model to bring the false positive rate on English-as-a-second-language writing down to 1%, and notes detection is strongest on longer English prose.

2. Turnitin

Best for: universities that already license Turnitin for plagiarism checks · Price: institutional subscription only; no individual license (as of Oct 2026) · Free plan: no

Turnitin builds AI writing detection into the similarity reports instructors already use. In a 2023 update, Turnitin said its document false positive rate is below 1% for documents with 20% or more AI writing, a figure it checked against 800,000 academic writing samples written before ChatGPT was released. It also says false positives are more frequent below 20%, so its current guide shows scores from 1% to 19% as an asterisk (*%) with no number.

Caveats: Turnitin's help center says it does not sell individual licenses or single-use subscriptions, so a writer cannot buy access to check their own work before submitting. Turnitin also puts its sentence-level false positive rate at around 4%, so a highlighted sentence is weaker evidence than a document score. Vanderbilt chose to switch the AI indicator off.

3. Originality.ai

Best for: publishers and agencies checking web content at volume · Price: Pro $14.95/month, or $12.95/month billed annually (as of Oct 2026) · Free plan: yes

Originality.ai bundles AI detection with plagiarism checks, readability, a fact checker and full-site scans. The free Basic plan allows 3 AI-only scans a day of up to 2,000 words each. Pro includes 2,000 credits a month, where 1 credit covers 100 words, and the Chrome extension with writing replay in Google Docs. Enterprise costs $179 a month, or $136.58 billed annually, for 15,000 credits, API access and a year of scan history.

Claims and caveats: Originality.ai publishes a roundup of academic studies in which its detector scored well. That roundup is compiled by the vendor, so read the linked studies for their datasets; several tested older models such as GPT-3.5 and GPT-4.

4. Pangram

Best for: editors and academics who care most about false positives · Price: Individual $20/month; Professional $65/month (as of Oct 2026) · Free plan: yes

Pangram's free plan scans up to 2,000 words a day, with file upload, OCR for scanned documents, detection in more than 20 languages, a browser extension and Google Docs integration. Individual covers 300,000 words a month with plagiarism detection on every scan. Professional adds 5x the words and $200 of API credits a month. Annual billing saves $60 on Individual.

Claims and caveats: Pangram publishes a roundup of outside evaluations. It reports 97.5% detection on fully AI-generated text and zero false positives on ESL essays, citing a peer-reviewed study from Vrije Universiteit Brussel that tested Pangram, GPTZero, Turnitin and Copyleaks on 160 academic papers, and that University of Chicago researchers found it was the only detector to meet a strict policy cap of a 0.5% false positive rate. These are Pangram's summaries of other people's work; the original papers set the conditions.

5. Grammarly AI Detector

Best for: a quick free check by the writer before submitting · Price: free; included in Grammarly Pro at $12/month billed annually (as of Oct 2026) · Free plan: yes

Grammarly's free AI Detector gives a score for how much of a text appears AI-generated. Grammarly says it reaches 99% detection accuracy, ranks first on the independent RAID benchmark, and is designed to reduce false positives. Grammarly Pro adds AI and plagiarism detection to its writing tools, and Grammarly Authorship records where text in a document came from, which helps a writer show their process.

Caveats: Grammarly's own FAQ says no detector can definitively conclude whether AI was used. Treat the score as a reason to review the text more closely.

How to act on a detector score

1. Read the text yourself first. Look for claims without sources, generic examples, or a voice that does not match the writer's earlier work.
2. Use more than one signal. Version history, drafts, writing replay or notes say more about process than any score.
3. Talk to the writer. Ask them to explain a section or a choice they made. People who wrote the text can usually do this easily.
4. Set the policy before the check. Writers should know in advance which AI use is allowed and how disclosure works.

For teachers, a short conversation is often the fairest check. This prompt drafts the questions:

I teach [subject] to [grade or level]. A student submitted an essay on [topic].
Write 6 short questions I can ask in a 5-minute conversation to check they understand their own argument.
Mix questions about their main claim, one piece of evidence they chose, and what they would change.
Avoid yes/no questions. Here is the essay: [paste essay]

More classroom prompts are in our education prompts. If you are choosing tools that help people write rather than check writing, see the best AI writing tools.

FAQ

What is the most accurate AI detector?

Every vendor here claims top accuracy, usually from its own tests or its own summary of others' tests. Independent studies from 2023 found detectors unreliable and biased against non-native English writers. Pick a tool whose evaluation data matches your kind of text, and never rely on one score.

Can AI detectors be wrong about human writing?

Yes. Turnitin itself says false positives are more frequent when it detects under 20% AI writing, and the Liang et al. study found non-native English writing was often misclassified as AI-generated.

Are there free online AI detection tools?

Yes. Grammarly's AI Detector is free, GPTZero scans up to 10,000 characters for free, Originality.ai allows 3 free scans a day, and Pangram's free plan covers 2,000 words a day. Other no-cost tools are collected in free AI tools.

Should a teacher fail a student based on an AI detector?

The vendors and the research both say no. Grammarly says detectors cannot definitively conclude AI use, and Vanderbilt disabled Turnitin's detector partly over concern about false positives. Use the score to decide which work to discuss.