Rendering

Rendering is the step where a search engine runs a page's HTML, CSS, and JavaScript to build the final version of the content the way a browser would.

Crawling fetches the raw response, but a modern page is often not complete until scripts run and build the rest of the DOM. Rendering is how a search engine sees that finished result. Google performs it with the Web Rendering Service, a system based on a current version of Chromium, which executes the page's JavaScript and produces the rendered HTML that indexing actually evaluates.

This matters most for JavaScript-heavy sites. If important content, links, or metadata only appear after scripts run, then indexing depends on rendering succeeding. Google processes rendering as part of its pipeline, and while it has become fast, it is not guaranteed to be instant or complete for every page; scripts that fail, time out, or depend on user interaction may leave content unseen. Content present in the initial HTML never has this risk, which is why server-side rendering and pre-rendering are recommended for critical content.

To check what a search engine renders, use the URL Inspection tool in Search Console, which shows the rendered HTML and screenshot Google produced, or compare the raw source against the rendered DOM. A gap between them, where text or links exist only after JavaScript runs, is a sign that important content depends on rendering and should be made available earlier in the load.

Related: Pre-rendering, JavaScript SEO and rendering guide, The forgotten HTML