Server Components Performance Tracks

What They Are

React can emit Server Components performance tracks — timing for how long each server component took to render, shown as a dedicated Server Components track in the Chrome DevTools Performance panel. Waku wires this up in the dev server, so there is nothing to configure.

Viewing the Track

1. Run your app in development with waku dev.
2. Open the page in Chrome and open DevTools.
3. Go to the Performance panel and click Record and reload.
4. Once the page has finished rendering, stop the recording.
5. Find the Server Components track. Each server component appears as a named entry; on React 19.3 or newer the entries also carry render durations, and nested awaits show up as a staircase.

Both the initial SSR render and later client navigations contribute entries.

If Component Spans Do Not Appear

This feature relies on React development internals, which Waku patches so that its RSC payload keeps the debug information React needs to build the track. That patch targets a specific React version, so mismatched versions are the usual cause of missing spans:

• The transform matches React's development build by an exact source string, so it is tied to the React version. It is currently verified against react, react-dom, and react-server-dom-webpack at 19.2.8 (Waku's own dependency, checked by an automated test). Use that version for all three packages; a different React release is the usual cause of missing spans.
• On React 19.2.x each server component shows as a named marker in the track; the render durations (the staircase spans) require React 19.3 or newer.

This is a development-only, best-effort aid; it has no effect on production builds.