Lab Data (Synthetic Monitoring)
Lab data is performance data collected in a controlled, repeatable environment using tools like Google Lighthouse or WebPageTest. The test is always run from the same location, on the same device profile, and with the same network speed. This consistency makes lab data excellent for debugging specific issues and for running automated checks to prevent performance regressions. However, it does not represent the varied and often slower conditions of real users, which is why Field Data is also essential.
Related web performance terms
- Largest Contentful Paint (LCP)
A Core Web Vital that measures the perceived loading speed of a page. It marks the point in time when the largest content element (usually a hero image or a large block of text) becomes visible within the viewport.
- Largest Contentful Paint Subparts
The LCP Subparts are the distinct phases that make up the total Largest Contentful Paint time. Analyzing this breakdown is crucial for diagnosing the root cause of a slow LCP.
- Layout Thrashing
Layout Thrashing is a harmful performance anti-pattern.
- Lazy loading
Lazy loading is an optimization strategy where content that is not immediately visible to the user—typically images and videos "below the fold"—is deferred and only loaded as the user scrolls down…