JPlag vs Noplag

JPlag is free software for finding pairwise similarities among programs that may indicate source-code plagiarism or collusion. It examines programming-language syntax and program structure, helping identify overlap even when code has been partly obfuscated. Analysis runs locally on the user’s machine, and the project says no data is sent externally. Comparisons are between submitted programs rather than internet sources. Listed language support includes Java, C, C++, C#, Python, JavaScript, TypeScript, Go, Kotlin, R, Rust, Swift, Scala, LLVM IR, Scheme, EMF, SCXML, text, and multi-language submissions, with varying maturity. Users can run the command-line interface or Java API, launch a report viewer from the CLI, or add JPlag through Maven Central. Reports show at most 2,500 pairs by default, adjustable with the -n option. Lower minimum matching-token lengths increase sensitivity but can also increase false positives. Running or building requires Java SE 25.

Noplag is an open-source plagiarism checker with a hosted cloud service and an engine released under Apache 2.0. Its current matching uses winnowing fingerprints and live-web comparison to find verbatim and near-verbatim copying; it does not detect paraphrase. Sources include the open web, Common Crawl, Wikipedia, academic indexes, the Noplag Database and users’ own folders. Submit DOCX, PDF, TXT, ODT or RTF files, paste text or provide a URL. Reports link matches to their sources, display similarity scores and exact overlapping text, and can be exported as PDFs. Detection is calibrated at launch for English, Spanish, Portuguese, Polish and Ukrainian. AI-content detection is marked as coming soon and intended as a separate signal. The free plan allows three checks per month, up to 2,500 words per check, with community Discord support. Pro costs $9.99 a month and includes 50 monthly checks, up to 25,000 words per check, database and academic-index matching, REST API and webhooks, and email support. A 14-day trial is listed.