Plagiarism checkers
We put 6 plagiarism checkers through the same test. Plagium came out on top with 3 out of 5. Here are all the results, what each tool costs and how we test them.
Plagiarism checkers we tested
Best score first. Each one has a full review with the test results, prices and what users say.
Plagium
3/5Read our review →
Quetext
3/5Read our review →
PlagiarismCheck.org
2.5/5Read our review →
SmallSEOTools
2.5/5Read our review →
Copyscape
2/5Read our review →
Scribbr
2/5Read our review →Test results compared
Every tool got the same test, between October 25, 2026 to October 31, 2026.
| Tool | Score | Accuracy on the labelled set | False positives (flagging something innocent) | False negatives (missing a real case) | Speed per item or per batch | Cost per 1,000 checks |
|---|---|---|---|---|---|---|
| Plagium | 3/5 | Correct 40/50 (80.0%) | False positives 3/20 (15.0%) | False negatives 7/30 (23.3%) | 21.7 sec/item | – |
| Quetext | 3/5 | Correct 41/50 (82.0%) | False positives 3/20 (15.0%) | False negatives 6/30 (20.0%) | 25.5 sec/item | – |
| PlagiarismCheck.org | 2.5/5 | Correct 38/50 (76.0%) | False positives 4/20 (20.0%) | False negatives 8/30 (26.7%) | 27.9 sec/item | – |
| SmallSEOTools | 2.5/5 | Correct 38/50 (76.0%) | False positives 4/20 (20.0%) | False negatives 8/30 (26.7%) | 26.6 sec/item | – |
| Copyscape | 2/5 | Correct 37/50 (74.0%) | False positives 4/20 (20.0%) | False negatives 9/30 (30.0%) | 23.7 sec/item | – |
| Scribbr | 2/5 | Correct 36/50 (72.0%) | False positives 4/20 (20.0%) | False negatives 10/30 (33.3%) | 29.9 sec/item | – |
Want just the shortlist?
Our best-of list ranks every tool in this test, with what each one is best for.
What plagiarism checkers do
Who uses them: Students checking theses and essays before submitting, Teachers and schools, Publishers and editors vetting freelancers, SEO and content teams guarding against scraped or duplicate content, Freelance writers proving originality.
Price range: Free tiers are small: Quetext 1,000 words, Plagium 2 to 5 searches a day of 2,000 characters, PlagiarismCheck.org a 2-page check, Copyscape free URL search with 10 results. Paid options range from cents per search (Copyscape) and 2 USD single documents (Plagium) to 19.95 to 39.95 USD per document (Scribbr) and 14.99 to 29.98 USD a month for subscriptions (Quetext). Turnitin is sold only to institutions. School plans are by quote.
What to check before you buy
. Matches depend on what is searched: the public web only (Copyscape via Google), web plus academic and paper repositories (Scribbr, per third parties), or web plus news and archives (Plagium Deep search).
Pricing model. Per document (Scribbr, 19.95 to 39.95 USD), per search (Copyscape, 3 cents), credits (Plagium), or monthly word allowance (Quetext, 14.99 USD for 100,000 words). Match it to how often you check.
Paraphrase detection. Copy-paste is easy to catch.
AI detection bundled. Roundups say good checkers now include AI detection; scores are probabilities and can falsely flag human work (a Copyscape user reported human poetry flagged as 99 percent AI).
Privacy and retention. Check whether documents are stored, added to databases or used for AI training (Quetext allows training by default with an opt-out; Scribbr terms describe private storage).
How we test plagiarism checkers
The test for this category: 50 documents with known copied, paraphrased and original passages; detection rate and false matches.
A labelled test set where the right answer is known in advance: for example 100 texts (human, AI and mixed) for AI detectors, 50 documents with planted copied passages for plagiarism checkers, 1,000 email addresses with known status for verifiers.
Each tool is tested on a paid plan, and its review shows the plan, the price and the test dates. The overall score is the average of the five parts on the right, rounded to the nearest half star. See the full method for detection and verification tools.
What we measure
- Accuracy on the labelled set
- False positives (flagging something innocent)
- False negatives (missing a real case)
- Speed per item or per batch
- Cost per 1,000 checks
The five parts of the score
Frequently asked questions
What is the best free plagiarism checker?
Free tiers are limited: Quetext 1,000 words, Plagium 2 to 5 short searches a day, PlagiarismCheck.org 2 pages, Copyscape URL search with 10 results.
Is Scribbr's plagiarism checker accurate?
Scribbr cites 88 percent detection in its own 12-tool benchmark; it is vendor-run and was not independently verified.
Can a plagiarism checker detect AI writing?
Most now bundle an AI detector that gives a probability; makers and Copyscape warn results can be wrong and should not be used alone for discipline.
Will my document be stored?
It varies: Quetext may use content for AI training unless you opt out; Scribbr says not in public databases but terms allow private storage; Copyscape's FAQ does not say.
Is Copyscape worth it?
It is cheap per search and suits web duplicate checks, but only searches the public web via Google and has few reviews.
Mia Chen
I've always loved the creative side of technology. I'm particularly interested in user experience and how small design decisions can completely change the way a platform feels.
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