I built a thing…
YAM (Yet Another MOSS) is a free and open-source code plagiarism / similarity detector that runs entirely on your own machine.
It combines classic token/winnowing comparison with Abstract Syntax Tree analysis, so it catches more than simple copy-paste: variable renaming, reformatting, reordering, and other cosmetic changes that leave the underlying structure intact.
Key points:
100% local – student code never leaves your computer (big win for privacy, FERPA, GDPR, etc.)
Modern, minimalist UI that makes it easy to spot the real problem cases without drowning in noise
Multiple ways to run it: headless, pure CLI, CLI + browser view, or simple server mode
Clean CSV and JSON output so you can pipe results into spreadsheets or other tools
Fully configurable (thresholds, k-gram size, window size, language options, etc.)
Free and open source (GitLab)
No accounts, no uploads, no external services. Just install and run.
Repo: https://gitlab.com/sylvan.wood.carving-group/yam
Happy to answer questions or take feedback.