JPlag
Source-code plagiarism detector that finds pairwise similarities among student programs across many languages.
Compare submissions locally, then explore the matches in a browser report viewer.
JPlag finds similarities among a set of programs and can detect software plagiarism and collusion even when code is obfuscated. It suits teachers and teaching assistants who grade programming assignments.
What it is
You point the Java command-line tool at a folder of submissions, pick a language, and it builds a report that opens in a browser viewer. All similarity is calculated locally, and no source code or results are uploaded, per the README.
Who it's for
It suits instructors with programming courses and some comfort with Java tooling. It compares code only, so it does not help with essays or AI-written prose, and every flagged pair still needs a human to judge it.
Key features
Pairwise similarity detection
Compares every submission with every other one and ranks the matches.
Many languages
Supports a long list of languages, with a -l option or a subcommand to choose one.
Report viewer
The CLI opens an interactive viewer in your browser for each comparison.
Prior submissions
The -old option lets you compare against earlier years' work.
Base code exclusion
The -bc option removes common framework code given to all students.
Java API and Maven
Use it from your own Java code via Maven Central.
Up and running in 3 steps
Our honest verdict
What's great
- All checks run locally, so student code is not uploaded.
- Handles many programming languages, with normalization for Java and C++.
- Base-code exclusion cuts false matches from provided skeleton code.
- Backed by an academic project with a wiki and a public demo.
Where it falls short
- Needs Java SE 25, which is newer than many lab machines have.
- GPL-3.0 licence: sharing source is required if you distribute changes.
- Compares submissions you supply; it does not search the web or detect AI-written text.
- The CLI and wiki are aimed at technical staff, not non-technical users.
Pricing & license
JPlag is free under the GPL-3.0 licence. The README shows no paid plan or hosted service, so the only cost is the Java machine you run it on.
Open remote AI-training roles
870 open remote AI-training roles, updated November 14, 2026; most pay $20–$170 an hour. Zekai lists them free; the application goes to the employer’s platform.
Alternatives
These reviewed AI tools do the same job instantly — from our scored directory.
Use it, or have us set it up
FAQ
Does JPlag upload student code?
No. The README says all similarities are calculated locally and no source code or results are uploaded.
Can JPlag check essays?
No. It compares source code only and does not read prose.
What Java version does it need?
The README says you need Java SE 25 to run or build JPlag.
