Browser Rendering Pipeline and Performance

Most page performance issues trace back to a stage in the rendering pipeline.

Critical rendering path

HTML parsing builds the DOM → CSS builds the CSSOM → merged into the render tree → layout → paint → composite. Any stall shows up as user-visible latency.

Optimization checklist

• Reduce render-blocking CSS/JS
• Lazy-load images with explicit dimensions
• Avoid layout thrashing (reflow)
• Slice long tasks or hand them to a Web Worker