Inside the Web Browser’s Performance API

The article discusses how modern web browsers expose performance data that can help developers understand their website's performance from an end-user perspective. It introduces the Performance API, which consists of several individual APIs such as Navigation Timing, Resource Timing, and Paint Timing. These APIs provide timing information related to page navigation, loading of application resources, and paint operations during page construction respectively. The article primarily focuses on the Navigation Timing API and demonstrates how developers can use it to measure performance metrics like DNS query time, TCP connection establishment time, request and response times, document rendering time, load event duration, and total time. It also explains how Cloudflare uses these performance data to identify slowdowns or network issues on a website. The article concludes by mentioning future plans for Browser Insights, such as incorporating metrics from other APIs, tracking JavaScript errors, setting up monitoring/alerting based on the metrics, and more.