sitespeed.io is a web performance analysis tool that runs real browsers to test, monitor, and optimize website speed across various environments.
The tool addresses the need to understand why websites are slow and track performance over time. It drives real browsers—Firefox, Chrome, Edge, or Safari, including Safari on physical iPhones over USB—to load pages and collects comprehensive metrics including Core Web Vitals scored against Google's p75 thresholds, filmstrip videos with visual metrics like Speed Index and First Visual Change, HAR waterfalls, best-practice advice from its Coach component, and CPU and long-task analysis. Results can be viewed as an HTML report for one-off audits or shipped to Graphite or InfluxDB for continuous monitoring in Grafana dashboards.
The tool suits three primary workflows: terminal-based audits to debug individual slow pages, CI regression testing to fail builds when performance budgets are exceeded, and production monitoring via scheduled runs with metrics tracked over time. It requires a browser installed locally plus FFmpeg and Python for video and visual metrics, though Docker images ship with Firefox, Chrome, Edge and all dependencies included. The README emphasizes that sitespeed.io has been available since 2012, is free, requires no signup, and keeps all data under your control.
The project maintains active development with regular updates to its changelog. Documentation is comprehensive, covering installation, configuration, scripting, and monitoring workflows. The tool supports advanced configuration through numerous flags and includes specific support for mobile testing on real Android phones over USB. Community engagement is present through social channels and contribution guidelines.
