Prometheus is an open-source systems and service monitoring toolkit originally built at SoundCloud in 2012 by engineers who found existing StatsD- and Graphite-based tooling couldn't keep up with a rapidly changing containerized infrastructure. It scrapes metrics from configured targets over HTTP on a defined interval, stores them in its own multi-dimensional time-series database keyed by metric name and label sets, and exposes PromQL, a purpose-built query language for slicing, aggregating, and alerting on that data. A separate Alertmanager component handles deduplication, grouping, and routing of alerts to channels like Slack, PagerDuty, or email. Accepted into the Cloud Native Computing Foundation in 2016 as its second hosted project after Kubernetes and graduated in 2018, Prometheus is released entirely under the Apache 2.0 license and is commonly paired with Grafana for visualization.