This plugin captures real user metrics about what elements are displayed on the page across a variety of device form factors (e.g. desktop, tablet, and phone) in order to apply loading optimizations which are not possible with WordPress’s current server-side heuristics.
This plugin is a framework dependency which does not provide optimization functionality on its own. For that, please install the Image Prioritizer and Embed Optimizer dependent plugins (among others to come from the WordPress Core Performance team). There are currently no settings and no user interface for this plugin since it is designed to work without any configuration.
Your site must currently have the REST API accessible to unauthenticated frontend visitors since this is how real user metrics are collected about pages on your site; nevertheless, exploration is underway for providing alternative mechanisms for collecting the metrics. Also, please note that no metrics are currently collected from Safari since it does not yet support the Largest Contentful Paint metric, but support for this Core Web Vitals metric is coming this year via Interop 2025.
Please refer to the full plugin documentation for a technical introduction, filter/action hooks, and extensions that show use cases and examples. You can also watch the talk from WordCamp Asia 2025: Boosting Performance with Optimization Detective.
