Many modern websites render content with JavaScript on the client side. While browsers handle this seamlessly, some search engine crawlers process JavaScript slowly or inconsistently, meaning key content may be invisible to them.
Dynamic rendering solves this with a middleware layer that intercepts requests. When the user-agent belongs to a known crawler, the middleware serves a fully pre-rendered HTML snapshot. Human visitors receive the standard JavaScript application.
When to use it: Dynamic rendering is a workaround for sites where server-side rendering (SSR) is not feasible. It is effective for JavaScript-heavy SPAs that cannot easily be refactored, though SSR is the preferred long-term solution.
What SearchVitals checks: The Architecture JavaScript Rendering check compares what a standard browser sees versus what a crawler sees. A material content difference triggers a critical or warning finding.