Time to first byte
Time to first byte, TTFB, is the interval from the start of the request to the arrival of the first byte of the response. Good is under 0.8 seconds and poor is over 1.8 seconds, as web.dev publishes them. It is not a Core Web Vital, but every other timing inherits it.
By Théophile Louvart, founder of Porteur · Updated 15 September 2026 · Markdown
What the number contains
- Any redirects, each with its own round trip.
- The DNS lookup, if the host is not already resolved.
- The TCP connection and the TLS handshake.
- The server’s own work: routing, database calls, rendering.
- The first byte travelling back to the browser.
The thresholds and where to read them
| TTFB | Reading |
|---|---|
| Under 0.8 s | Good |
| 0.8 s to 1.8 s | Needs improvement |
| Over 1.8 s | Poor |
PageSpeed Insights shows it in the field section when your site has enough traffic, and in the diagnostics of the lab run as the server response time. A browser’s network panel shows it per request under Waiting.
What improves it
Cache or pre-render the HTML
A page built at request time on every visit pays for that work every visit. Static generation or a cached response removes it.
Put a CDN in front
Most of a slow first byte for a distant visitor is distance. A CDN answers from near them.
Remove the redirects
Point the first URL straight at the final one. Each hop removed is a round trip saved.
Turn on HTTP/2 or HTTP/3
Both remove connection overhead; they are set at the server or the CDN and cost nothing to the page.
Make the server work less
The database call in the layout that runs on every page is the usual culprit on a small site.
Questions
Under 0.8 seconds is good and over 1.8 seconds is poor, as web.dev publishes the thresholds. Between the two is worth improving when other work is done.
Not directly. It is not a Core Web Vital. It is inherited by First Contentful Paint and Largest Contentful Paint, which do count, so a slow first byte costs you through them.
Usually distance and cache state. A visitor near your server with a warm cache gets a fast response; one on another continent hitting a cold page waits for the round trips and the render.
It fixes the distance part, which is often most of it. It cannot fix a server that takes a second to build the page, unless the CDN can cache that page.
The field section of PageSpeed Insights for real visitors, the network panel of a browser for one request, or a server response check that reports the first byte for a URL you paste.
Check my site, free
The free check measures how your home page answers and paints on a phone, and names the first thing to fix, in about thirty seconds.
- Free check, no card
- Read-only, your own accounts
- Readable by your agent