What is TTFB (Time to First Bite)?

Purpose

Define Time to First Byte (TTFB), explain what it represents, and clarify how it relates to Speed Layer.

What TTFB measures

TTFB measures how long it takes for the browser to receive the first byte of the page response after making a request. It is largely a server and network signal.

Google reference:

TTFB guidance https://web.dev/ttfb/

What affects TTFB

Hosting and server performance
CDN caching behavior
Backend application and database latency
Network distance and congestion

How Speed Layer relates to TTFB

Speed Layer runs in the browser after the HTML begins loading. It can improve how the browser handles work during render and interaction.

Speed Layer does not directly reduce server response time. If TTFB is consistently slow, improvements typically require server, CDN, or application changes.

How to use TTFB when diagnosing slow pages

If LCP is slow and TTFB is also slow, server response may be part of the problem.
If TTFB is fine and LCP is slow, the issue is often render and execution work in the browser.

Backend server performance
What Is LCP (Largest Contentful Paint)?
Why Real User Experience Matters More Than Scores