WordPress.org

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 <a href="https://wordpress.org/plugins/image-prioritizer/" rel="ugc">Image Prioritizer</a> and <a href="https://wordpress.org/plugins/embed-optimizer/" rel="ugc">Embed Optimizer</a> dependent plugins (among <a href="https://github.com/WordPress/performance/labels/%5BPlugin%5D%20Optimization%20Detective" rel="nofollow ugc">others</a> 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, <a href="https://github.com/WordPress/performance/issues/1311" rel="nofollow ugc">exploration</a> 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 <a href="https://developer.mozilla.org/en-US/docs/Web/API/LargestContentfulPaint" rel="nofollow ugc">Largest Contentful Paint</a> metric, but support for this <a href="https://web.dev/explore/learn-core-web-vitals" rel="nofollow ugc">Core Web Vitals</a> metric is coming this year <a href="https://webkit.org/blog/16458/announcing-interop-2025/#core-web-vitals" rel="nofollow ugc">via Interop 2025</a>.
Please refer to the <a href="https://github.com/WordPress/performance/blob/trunk/plugins/optimization-detective/docs/README.md" rel="nofollow ugc">full plugin documentation</a> for a <a href="https://github.com/WordPress/performance/blob/trunk/plugins/optimization-detective/docs/introduction.md" rel="nofollow ugc">technical introduction</a>, <a href="https://github.com/WordPress/performance/blob/trunk/plugins/optimization-detective/docs/hooks.md" rel="nofollow ugc">filter/action hooks</a>, and <a href="https://github.com/WordPress/performance/blob/trunk/plugins/optimization-detective/docs/extensions.md" rel="nofollow ugc">extensions</a> that show use cases and examples. You can also watch the talk from WordCamp Asia 2025: <a href="https://weston.ruter.net/2025/02/21/boosting-performance-with-optimization-detective/" rel="nofollow ugc">Boosting Performance with Optimization Detective</a>.

Optimization Detective

Provides a framework for leveraging real user metrics to detect optimizations for improving page performance.

watchlog

Watchlog RUM delivers Real User Monitoring for WordPress sites by mirroring the Watchlog Vue/React SDK event format. It tracks session lifecycle events, performance metrics, network activity, resource usage, and optional Web Vitals so you can understand how visitors experience your site in production.
<ul>
<li>Automatic <code>session_start</code>, <code>page_view</code>, and <code>session_end</code> events.</li>
<li>Navigation/paint timings plus optional Web Vitals (CLS, LCP, INP, TTFB, FID).</li>
<li>Instrumentation for <code>fetch</code>, <code>XMLHttpRequest</code>, long tasks, resources, and user interactions.</li>
<li>Breadcrumb and error capture hooks to enrich every event.</li>
<li>WordPress-aware route normalization and session persistence to align data with SPA SDKs.</li>
</ul>
<h3>Third-Party Libraries</h3>
<ul>
<li>web-vitals (GoogleChrome/web-vitals) — Source: https://github.com/GoogleChrome/web-vitals — License: Apache-2.0 — Bundled file: assets/js/web-vitals.iife.js</li>
</ul>

Watchlog RUM

Real User Monitoring (RUM) for WordPress powered by Watchlog.

Optimization Detective vs Watchlog RUM