Spec - LCP - W3C
A web performance metric that measures the render time of the largest contentful element visible in the viewport.
What is Spec - LCP - W3C?
Largest Contentful Paint (LCP) is a web performance metric that measures the render time of the largest contentful element (such as an image, text block, or video poster) visible in the viewport during page load. It is designed to better correlate with user-perceived page load experience than earlier metrics like First Paint or First Contentful Paint by focusing on when the main content becomes visible. The metric provides a single, interpretable value that helps developers assess how quickly a page delivers its primary content.
Web developers, performance engineers, and site reliability engineers who need to measure and optimize real-world user experience for page load performance, particularly those working on content-heavy websites or applications where visual rendering speed is critical.
Developers choose LCP over alternatives because it offers a simpler, more reliable heuristic than complex metrics like First Meaningful Paint (FMP), avoiding outlier results while focusing on the largest visible element as a proxy for main content. It is standardized, implemented consistently across browsers via the PerformanceObserver API, and handles edge cases like removed elements (e.g., in carousels) and user interactions to provide a more accurate reflection of perceived load speed.
Overview
Specification for the LargestContentfulPaint API
Use Cases
Best For
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