Bosun is a monitoring and alerting solution released under the MIT license by Stack Exchange, designed to be open-source. It features a powerful domain-specific language that allows users to evaluate alerts and generate comprehensive notifications. The system enables users to test their alerts against historical data, thereby streamlining the development process significantly. Its flexible expression language facilitates precise evaluation of time series data, allowing for meticulous monitoring. By leveraging historical data for testing alerts, users can minimize alert fatigue and ensure only relevant notifications are triggered when the system goes live. Bosun is compatible with various operating systems, including Linux, Windows, and Mac, as well as any OS supported by Go. The system supports arbitrary dimensions beyond just host-based metrics, offers aggregation capabilities, and automatically integrates new tags as they become available. Additionally, Scollector identifies new services autonomously and begins transmitting metrics without delay, which means that well-designed alerts can extend to these new services with reduced administrative effort. Finally, users can employ the Scollector agent to monitor not only Windows and Linux systems but also a range of common applications, ensuring comprehensive coverage across their infrastructure.