Glossaire · SEO

TTFB (Time To First Byte)

TTFB (Time To First Byte) is the measure of the time elapsed between the moment the browser sends an HTTP request and the moment it receives the very first byte of the server's response. Expressed in milliseconds, it aggregates three phases: DNS resolution, the TCP/TLS connection setup, then the server-side processing time. TTFB is a key indicator of infrastructure responsiveness: it determines when every other loading event can begin. Google recommends a TTFB below 800 milliseconds for 75% of visits. Although it is not an official Core Web Vital, it directly influences LCP and perceived speed. A high TTFB often reveals a slow server, an overloaded database, a lack of caching, or hosting located far from the users it serves.

TTFB is one of the first performance signals a visitor perceives, even if it remains invisible. Until the first byte arrives, the browser waits, the screen stays blank, and every millisecond counts toward the perception of speed.

How TTFB breaks down

TTFB adds up several successive steps that occur before a single pixel is displayed:

Any redirects (each hop adds delay).
DNS resolution: translating the domain name into an IP address.
TCP connection and TLS negotiation: establishing the secure channel.
Server processing time: generating the response, database queries, application code execution.

It is usually server processing that weighs the most, especially on dynamic or poorly cached sites.

Why TTFB matters for SEO

TTFB does not trigger a direct penalty, but it sits upstream of the entire loading chain. A slow TTFB mechanically delays LCP, which is part of the Core Web Vitals used as a page experience signal. A slow server also slows crawling: Googlebot explores fewer pages when every response lags.

Key takeaway

TTFB is the ceiling on your speed: no front-end optimization can compensate for a server that responds in 2 seconds.

How to reduce your TTFB

The most effective levers combine infrastructure and caching:

Enable server caching (page cache, OPcache) and a CDN close to users.
Optimize database queries and application code.
Choose performant, geographically relevant hosting.
Favor server-side rendering with static generation whenever possible.

At LUWIZ, every performance audit systematically begins by measuring TTFB in real-world conditions using field data, before touching a single visual element.

FAQ

Questions fréquentes

Google recommends a TTFB below 800 milliseconds for a good experience. Above 1,800 ms, TTFB is considered poor and penalizes the page's loading.

TTFB is not a direct ranking factor, but it influences LCP, which is part of the Core Web Vitals. Improving TTFB therefore indirectly improves your page experience signal.

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