JPlag
JPlag is a free, open-source tool that identifies pairwise similarities among programs to help detect source-code plagiarism and collusion.
What JPlag is
JPlag is a free, open-source tool that identifies pairwise similarities among programs to help detect source-code plagiarism and collusion. It examines program syntax and structure rather than searching the internet. The project describes student programming exercises as a typical use and also notes that it can reveal duplicated or stolen software parts. JPlag supports Java, C, C++, C#, Python, JavaScript, TypeScript, Go, Kotlin, R, Rust, Swift, Scala, LLVM IR, Scheme, EMF, SCXML, text, and multi-language input. Run it from the command line, call it through its Java API, or include it in a Java project as a Maven Central dependency. Analysis runs locally; the project says source code and results are not sent externally. A bundled report viewer opens generated or existing reports. Shared starter code can be excluded, and matching sensitivity can be adjusted. Running or building JPlag requires Java SE 25. By default, reports list up to 2500 comparison pairs, adjustable with the -n option.
Good
- Free and open-source.
- Analysis runs locally; code and results stay unshared.
- Supports a broad range of languages and inputs.
- Offers command-line, Java API, and Maven options.
- Can exclude shared starter code.
Watch out
- Requires Java SE 25 to run or build.
- Does not compare submissions with the internet.
- Lower matching thresholds can increase false positives.
- Reports default to at most 2500 comparison pairs.
Who it suits
JPlag suits educators checking student programming work and teams looking for similar or reused software code. It is a fit for users who can run Java SE 25 and want local analysis.
Verdict
JPlag focuses on pairwise code comparison, with local processing and multiple ways to integrate it. Its Java SE 25 requirement and lack of internet matching are important constraints to consider.
Plans and prices
From JPlag's own pricing page, checked 11 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| JPlag | Free | Open-source software; runs locally; requires Java SE 25 |
The facts
Each one read from JPlag's own pages, with the date it was checked.
What it does
- Data handling
- The project states that analysis runs locally and that source code and plagiarism results are not uploaded or sent externally.checked 11 Oct 2026
- Exclude starter code
- A base-code directory can be specified so matches also present in the shared template are ignored.checked 11 Oct 2026
- How it compares
- JPlag analyzes program syntax and structure and is designed to find similarities among submitted programs; it does not compare them with the internet.checked 11 Oct 2026
- Integration
- JPlag is available as a dependency from Maven Central for inclusion in Java projects.checked 11 Oct 2026
- Purpose
- JPlag finds pairwise similarities among programs to detect source-code plagiarism and collusion.checked 11 Oct 2026
- Report limit
- The default report shows at most 2500 comparison pairs in its top list and code comparisons, configurable with the -n option.checked 11 Oct 2026
- Report viewer
- Since version 6.0.0, the report viewer is bundled with JPlag and can open generated or existing reports.checked 11 Oct 2026
- Requirements
- The project README says Java SE 25 is needed to run or build JPlag.checked 11 Oct 2026
- Run options
- JPlag can be run through its command-line interface or called programmatically through its Java API.checked 11 Oct 2026
- Sensitivity setting
- The minimum matching token length can be adjusted; lower values increase sensitivity but may cause more false positives.checked 11 Oct 2026
- Support
- The project directs users to report bugs and issues and provides [email protected] for other inquiries.checked 11 Oct 2026
- Supported languages
- The project lists support for Java, C, C++, C#, Python, JavaScript, TypeScript, Go, Kotlin, R, Rust, Swift, Scala, LLVM IR, Scheme, EMF, SCXML, text, and multi-language input.checked 11 Oct 2026
- Typical users
- The project says it is typically used to detect copying of student programming exercises and can also identify duplicated or stolen software parts.checked 11 Oct 2026
The company
- Founded
- 1996checked 28 Sep 2026
- Headquarters
- Karlsruhe, Germanychecked 28 Sep 2026
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