Medusa
Medusa is a lightweight, server-side Minecraft anti-cheat system built in Java to detect cheats like aimbots, autoclickers, and reach exploits using carefully tuned heuristic checks. With a 0.5-block tolerance reach check and reverse-engineered detection logic, Medusa delivers low false positives without requiring client mods. It has been deployed in production and downloaded over 26,000 times.
Below, you can watch a system design explanation for Medusa.
Our goal
Medusa was created to address a critical gap in the Minecraft server ecosystem: the lack of effective, accessible, and open-source anti-cheat solutions. At the time, most high-performing anti-cheats were locked behind paywalls, making it difficult for new developers and small servers to implement reliable cheat detection without investing in closed systems. This barrier limited innovation and made competitive integrity inaccessible to entry-level servers.
Medusa set out to change that by offering a free, fully customizable anti-cheat system that could scale from small communities to large networks. It featured in-game configuration tools, a flexible command system, and a public API for deeper integration, allowing server owners to tailor detections to their needs. Despite its accessibility, Medusa delivered top-tier performance, benchmarking 11.79x lighter than the leading paid competitor at the time, and included what was widely regarded as the most accurate free reach check available, with a 0.5-block tolerance. In direct comparisons, Medusa’s reach detection outperformed even Verus, a well-known paid solution.
Our goal was simple: empower the Minecraft server community with a transparent, performant anti-cheat system that didn't compromise on accuracy, flexibility, or resource efficiency.
The importance of user experience
In the anti-cheat landscape, performance and accuracy are critical, but user experience is just as important. Many open-source or even paid anti-cheat solutions fall short by locking users into rigid settings, offering no integration points, and providing little to no meaningful support. Medusa was built to change that.
Medusa prioritized user experience from the beginning by offering deep customizability and integration options. Server owners could fine tune check sensitivity values, configure mitigation thresholds, and even define custom commands to trigger on violations, allowing them to plug directly into third-party moderation or punishment systems. A built-in theming system made logs and messages consistent with server aesthetics, and an API enabled advanced users to integrate Medusa with larger, more complex server infrastructures.
Beyond features, user support was treated as a core component of Medusa’s offering. Until support concluded in 2021, over 80 user tickets were personally resolved via Discord. These ranged from bug reports and compatibility issues to configuration questions and optimization help. Many of Medusa’s improvements were directly shaped by this user feedback loop, which bridged the gap between developer and end user, something most competing anti-cheats failed to deliver.
While other systems remained opaque and rigid, Medusa stood out by putting users in control, ensuring the system could adapt to a wide variety of server environments, technical stacks, and gameplay contexts. In doing so, it not only improved detection, but trust.