First Contentful Paint (FCP)
Collected from: Web Browser (API)
First Contentful Paint measures the time it takes for content to start appearing on the page. Its definition is therefore very close to the Start Render. However, FCP is not computed through video analysis, but provided directly by the web browser (via the Paint Timing API).
Here is the exact definition as provided in the W3C specification (draft):
FCP is the point when the browser renders the first bit of content from the Document Object Model (DOM), which may be text, an image, SVG, or even a canvas element.
Despite its definition, FCP can be triggered even when nothing is visible yet. For example when the text is available on the page but invisible because a custom font (web font) is still loading.
For further details, on our blog: First Contentful Paint (FCP), Start Render, First Paint. How to properly measure the beginning of page rendering?