TTFB

TTFB (Time to First Byte) measures how long it takes for the very first byte of a server's response to arrive at the browser after a request is sent. It captures the delay before any content can begin rendering, combining the time spent resolving the address, establishing the connection and — most importantly — the server generating the response.

What TTFB tells you

A high TTFB usually points to slow work happening on the server: expensive database queries, unoptimised application code, or the absence of caching. Some of the delay comes from the network — the physical distance to the server and the time to set up the connection — but a large TTFB most often reflects how long the backend takes to produce the page. Because nothing can be displayed until the first byte arrives, TTFB sets a floor under how fast a page can feel.

Improving TTFB

Reducing TTFB has a direct effect on perceived speed and user experience. Caching is the most powerful lever: serving a ready-made response from memory, for instance through a reverse proxy cache, skips the slow work of regenerating the page. A CDN shortens the network portion by serving content from a location near the user. On the application side, optimising queries, reducing heavy processing and using efficient code all help. TTFB relates to the broader Core Web Vitals, since a slow server delays the metrics that measure loading experience. While TTFB is not the whole story — a fast first byte followed by heavy assets can still feel slow — it is a fundamental indicator of backend health, and keeping it low is one of the most effective ways to make a site feel responsive.