Free code plagiarism checker
Compare up to 20 students' code with each other for free, with no account. Upload one ZIP per student and get a similarity score for each, with the matching lines side by side. Renamed variables and reformatting do not hide a copy.
No account, no card. 3 free checks a week, in 65+ languages.
anagrams.pyanagrams.pyThe same function handed in twice with the names changed (highlighted). The free check compares structure, so renaming does not hide it.
Used in programming courses at
What the free check does
The free check is a group similarity check. It compares every submission you upload with every other one and reports the pairs that share code.
- It compares structure, not text. Names, comments and whitespace are ignored, so a renamed or reformatted copy still matches.
- It shows the evidence. Each match opens the two files side by side with the shared lines marked.
- It covers 65+ languages, from Python and Java to C++, Go and SQL.
- It needs nothing from you. No account and no card. You can run it 3 times a week.
What it does not check: the web and AI. A solution copied from GitHub, or written by ChatGPT, only shows up here if two students handed in the same one. The paid check covers both.
How to run it
- Zip each submission. One ZIP per student, up to 10 MB each. A ZIP can hold one file or a whole project.
- Open the free check and pick the programming language.
- Upload 2 to 20 ZIPs and start the check. Add an email if you want the results link sent to you.
- Read the results. Start with the highest scores and open each match to compare the lines. A high score means look closer, not guilty.
Compare your submissions now
No account needed. Results in minutes.
Free vs paid
| Free check | Single check, $44 | |
|---|---|---|
| Account needed | No | No |
| Compares students with each other | Yes | Yes |
| Checks GitHub, Stack Overflow and the web | No | Yes |
| Detects AI-written code | No | Yes |
| Submissions per check | 2 to 20 | Up to 20 |
| How often | 3 a week | Pay per check |
Checking a whole course every week? A Codequiry account checks every assignment against classmates, past terms, the web and AI, can connect to your LMS, and keeps every report. It starts with a 1-day free trial. See pricing.
Other free tools
If you are comfortable in a terminal, three free tools also compare submissions with each other:
- MOSS, from Stanford, free for academic use. You register by email and submit with a Perl script. Results are deleted after 14 days.
- JPlag, open source, runs on your own machine with Java.
- Dolos, open source from Ghent University, with a web interface you can host.
Like the free check here, none of them search the web or detect AI. There is a full comparison in MOSS vs Dolos vs JPlag, and MOSS alternative covers what MOSS misses.
Frequently asked questions
Is the free code plagiarism checker really free?
Yes. The group similarity check costs nothing and needs no account or card. You can run it 3 times a week.
Do I need to sign up?
No. Open the free check, upload the files and read the results. An email address is optional, only if you want the results link sent to you.
How many files can I check?
From 2 to 20 submissions per check, each as its own ZIP of up to 10 MB. For a larger class, use a Codequiry account.
Does the free check search the web or detect AI?
No. It compares the files you upload with each other. Checking GitHub, Stack Overflow and the web, and detecting AI-written code, is part of the paid check ($44 once) and of every plan.
Which programming languages does it support?
The same 65+ languages as the full product, including Python, Java, C, C++, C#, JavaScript, TypeScript, Go, Rust, Kotlin, Swift and SQL. You pick the language before you upload.
Can I check a single file?
Not with the free check, because it compares files with each other and needs at least two. To check one file against the web and AI, run a single paid check or paste it into Instant Check.
What happens to the code I upload?
It is used to run the check and may be kept and compared with future submissions, as described in the privacy policy. Do not upload code you are not allowed to share.
Check your submissions for free
Upload 2 to 20 ZIPs and see which students share code, with the lines side by side.
Run a free check Need the web and AI too? Run a single check