Custom Performance Metric

A custom performance metric is a user-defined measurement used to track the performance of specific, business-critical elements or interactions that are not captured by standard metrics. They are particularly useful when the Largest Contentful Paint (LCP) metric does not represent the most important element on the page. For instance, you can create a custom metric to measure the render time of a crucial but smaller element like a "Buy Now" button or a stock availability message, or to track the duration of a specific API call. These metrics are created using browser APIs like Element Timing and the User Timing API (`performance.mark` and `performance.measure`) and can be collected and analyzed in both Lab Data tools and Field Data (RUM) solutions.