Arthas is an open-source Java diagnostic tool from Alibaba for troubleshooting running JVM applications in production. It allows developers to inspect and analyze applications without changing source code or restarting the service, which is especially valuable when a problem cannot be reproduced in development or would disappear after a restart.

The tool can inspect loaded classes and classloaders, decompile classes, trace method calls, display parameters and return values, examine exceptions and call stacks, monitor QPS and response times, profile CPU usage, inspect threads and garbage collection, generate flame graphs, and retrieve heap objects. It provides an interactive command-line interface and supports local or remote diagnostics through technologies such as Telnet and WebSocket.

Arthas is designed for Java developers, SREs, and operations teams diagnosing live production systems where attaching a traditional debugger would be unsafe or impractical. By acting as an observer rather than suspending application threads, it provides a powerful middle ground between static logs and invasive debugging, with support for modern JDK versions across Linux, macOS, and Windows.