// About
A judge that turns
source into a verdict.
Verwandlung is an open-source, cross-platform online judge built on Spring Boot and a distributed pool of judgers coordinated through ActiveMQ. It compiles, runs, and grades submissions against hidden test cases in sandboxed runners. It is the same engine behind every contest and practice problem on this site.
// Architecture
Spring Boot
Java backend serving problems, submissions and contests.
ActiveMQ
Message broker that distributes judge jobs across the judger pool.
Judgers
Cross-platform sandboxed runners for Linux and Windows, under time and memory limits.
MySQL
Persistent store for users, problems, test data and verdicts.
MyBatis
SQL-mapping layer between the Spring services and the database.
Thymeleaf
Server-rendered views with no heavyweight SPA framework.
// Milestones
2014First commit, already with cross-platform judgers on Linux and Windows, rare among online judges.
2015ActiveMQ added, so the web app and judgers communicate over a message queue and judging can run across multiple machines.
2018Web and judger components containerized with Docker.
2023Upgraded to Spring 6 across both modules.
2026Rebuilt on Spring Boot 4 across the web and judger modules.
Native Linux and Windows sandboxes replace the legacy runner.
A brand-new UI design across the whole site.
// Maintainer
H
// Open Source