Can AI detectors be trusted?

As a signal, with heavy caveats: published evaluations show meaningful false-positive rates, particularly for non-native English writing. Never treat a score as proof.

What is the difference between AI detection and plagiarism checking?

Plagiarism compares text against existing published sources; AI detection estimates generation patterns. They are different checks and different products.

Do detectors work on paraphrased AI text?

Published studies show paraphrasing tools substantially reduce detection rates — treat any accuracy claim as conditional.

Should institutions use them?

Many do, as one input alongside process-based assessment — the tool profiles link each vendor's own documentation and limitations.

Category guide

AI Detection & Plagiarism Tools

Detection tools estimate whether text or images were AI-generated; plagiarism tools check overlap with existing sources. Both categories come with honest caveats: detection is probabilistic, false positives happen, and no tool is a proof.

4 verified tools3 with a free plan2 with API access

The comparison at a glance

Criterion	QuillBot	GPTZero	Originality.ai	CheckWise AI
Provider	QuillBot (Learneo)	—	—	CheckWise AI
What it is for	A suite of writing tools for paraphrasing, summarising, grammar checking and AI detection, popular with students.	An AI detection service that estimates whether a piece of text was written by a person, by an AI model, or by a mix of both.	An AI content detector and plagiarism checker aimed at publishers, agencies, writers and educators.	An independent document-analysis service that runs an AI-writing check and a similarity (plagiarism) check on the same upload.
Latest confirmed model	—	—	—	—
Main capabilities	Paraphraser (Depends on plan) Summarizer (Depends on plan) AI Detector (Depends on plan) Grammar checker Team plans	AI Detector that highlights passages it suspects are AI-generated and gives an overall estimate Classifies text as human, mixed or AI, with sentence-level highlights (via the API) Plagiarism Check and Advanced Scan on paid plans Writing Replay / authorship tool that shows how a document was written, including copy-and-paste activity Chrome extension and Google Docs add-on, plus integrations listed for Google Classroom, Canvas and Zapier	AI Checker with sentence highlights and shareable/PDF reports Plagiarism Checker and bulk scanning Fact and AI hallucination checker Readability and grammar/spelling checkers Chrome extension that scans in Google Docs and can replay the writing process	AI content analysis Similarity (plagiarism) check File upload or pasted text Downloadable reports Automatic data purge
Free plan	Yes Paraphraser 125 words per input; Summarizer 1,200 words; AI Detector 1,200 words per scan, 6 scans/day	Yes	Yes	No
Cheapest paid plan	Premium: $19.95/mo $8.33/mo billed annually Annual $99.95 billed yearly; monthly figure from QuillBot FAQ; regional pricing applies	Pricing not verified	Pricing not verified	No monthly list price
API access	No	Yes	Yes	No
Learning curve	Beginner-friendly	—	—	Beginner-friendly
Last verified	Oct 19, 2026	Oct 13, 2026	Oct 13, 2026	Oct 19, 2026

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How we would choose

Published accuracy rates are measured on specific test sets — they do not transfer to every kind of text.
False positives disproportionately affect non-native English writers — a documented, serious limitation.
Plagiarism checking and AI detection are different products; many tools sell both.

Advantages

A signal where you had none — useful alongside human judgement
Plagiarism checking against published sources is mature technology
Institutions can set thresholds and require human review

Limitations

No detector is accurate enough to accuse anyone on its output alone
Paraphrasing tools defeat simple detectors in published studies
Vendors of AI writing tools also sell detectors — a conflict to note

Practical use cases

Illustrative scenarios for this category — not customer case studies.

Editorial triage of submissions before human review
Originality checks on sources and student reference lists
Policy enforcement as one signal among several, never alone

Frequently asked questions

Can AI detectors be trusted?: As a signal, with heavy caveats: published evaluations show meaningful false-positive rates, particularly for non-native English writing. Never treat a score as proof.
What is the difference between AI detection and plagiarism checking?: Plagiarism compares text against existing published sources; AI detection estimates generation patterns. They are different checks and different products.
Do detectors work on paraphrased AI text?: Published studies show paraphrasing tools substantially reduce detection rates — treat any accuracy claim as conditional.
Should institutions use them?: Many do, as one input alongside process-based assessment — the tool profiles link each vendor's own documentation and limitations.

Related comparisons and guides

AI detection tools compared side by sideVerified data from the same directory.AI writing tools comparedVerified data from the same directory. The full AI tools directorySearch, filter and compare every verified tool.

The table shows up to five entries in the directory's editorial order, not a ranking. Every value links back to a record with sources and a last-verified date.