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Glossary

Time to First Byte (TTFB)

Nothing on the page can happen faster than the server starts answering.

By · Last updated: September 2026

TL;DR

Time to First Byte (TTFB) is the time from when a browser starts requesting a page to when the first byte of the response arrives. It includes redirects, DNS lookup, connection and TLS setup and the server's own processing. web.dev rates 0.8 seconds or less as good and over 1.8 seconds as poor.

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How it works

What is inside it

  1. 1
    Redirects — each one is a full extra round trip.
  2. 2
    DNS lookup — resolving the hostname.
  3. 3
    Connection and TLS — the TCP handshake and the HTTPS negotiation.
  4. 4
    Server processing — the application building the response: database queries, rendering, upstream API calls.
  5. 5
    First byte — the first packet of the response reaching the browser.

In the browser, performance.getEntriesByType("navigation")[0].responseStart is the TTFB of the current page, in milliseconds from navigation start.

In practice

Why it matters

TTFB is not a Core Web Vital, but it is the first slice of LCP: a page whose server takes 2 seconds to answer cannot have an LCP under 2.5 seconds unless everything after it is nearly instant. A redirect from http:// to https://www. can cost more than the server itself.

Typical fixes: serve cached HTML from a CDN close to the visitor, cache expensive queries, stream the response head before the body is ready, and link straight to the final URL instead of a redirect chain.

URLpipe

Measuring it with URLpipe

A /lighthouse audit's headline metrics include FCP, Speed Index, LCP, TBT and CLS, not TTFB; the server's response time is in the full audits, which include_audits: "true" adds, among Lighthouse's checks on the document request. Mobile runs simulate a slow 4G network, which inflates it.

Don't confirm TTFB from URLpipe's own response headers: X-Processing-Time-Ms is how long the whole analysis took — rendering included — not how long the target site took to answer.

Try it

Time to First Byte (TTFB), on a page you choose

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Related terms

Largest Contentful Paint (LCP)Speed IndexCache TTL (max_age)

FAQ

Frequently asked questions

What is a good TTFB?
0.8 seconds or less, according to web.dev. Above 1.8 seconds is poor.
Is TTFB a Core Web Vital?
No, but it is the first part of Largest Contentful Paint, so a slow TTFB makes a good LCP hard to reach.
Does a CDN improve TTFB?
Yes, when it can serve the HTML from cache near the visitor. A CDN that only caches images and scripts does not change the document's TTFB.

Keep reading

Cache, timing and quota on every responseFind JavaScript errors on any siteCheck a page's Core Web VitalsRun a Lighthouse audit in PythonLighthouse variance: how much does one audit move?Interaction to Next Paint (INP)All of glossary

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