Time to First ByteTTFB

Time to First Byte measures how long it takes for the first byte of the server response to reach the browser after a request. It rolls up DNS resolution, connection setup, TLS negotiation, request travel, and server processing time. A common target is under 800 milliseconds, though faster is always better because TTFB is the floor under LCP: you cannot paint the largest element before the HTML starts arriving.

TTFB is dominated by server and network factors: how fast the origin generates the response, how far the user is from the server, whether the response is cached at an edge, and whether the connection is warm. The biggest wins usually come from caching at a CDN edge, serving static or incrementally regenerated HTML instead of computing every request, and reducing slow database or API calls on the critical path.

For frameworks that support edge rendering and CDN caching, much of the TTFB problem is solved by architecture: serve the shell from the edge, stream the rest. We surface TTFB alongside server-timing headers where the origin exposes them, so a slow page can be traced to either the server or the network rather than guessed at.