In the ever-changing world of DevOps, where micro-services and distributed architectures are becoming the norm, the need to understand application internal state is growing rapidly. Whitebox monitoring gives you details about the internal state of your application, such as the total number of HTTP requests on your web server or the number of errors logged. In contrast, blackbox testing (e.g., Nagios) allows you to check a system or application (e.g., checking disk space, or pinging a host) to see if a host or service is alive, but does not help you understand how it may have gotten to the current state. Prometheus is an open source whitebox monitoring solution that uses a time-series database to provide scraping, querying, graphing and alerting based on time-series data. This blog post briefly explores the benefits of using Prometheus as a whitebox monitoring tool.