---
source: https://iinventedlight.com/library/notes/webdev-ttfb.md
title: "Time to First Byte (TTFB)"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "CC BY 4.0 (web.dev live page footer: 'the content of this page is licensed under the Creative Commons Attribution 4.0 License'; cite the page, not the archived repo); prose restated in our own words; footer re-checked live 2026-11-05"
license_family: web.dev
rule_check: "needs rule check (family not in auto-publish rule; check.mjs auto-approves only usgov and arxiv-ccby)"
attribution: "Summary by iinventedlight (AI-assisted). Sources: Google (web.dev), Time to First Byte (TTFB)  |  Articles  |  web.dev, CC BY 4.0 (web.dev live page footer: 'the content of this page is licensed under the Creative Commons Attribution 4.0 License'; cite the page, not the archived repo); Google (web.dev), Optimize Time to First Byte  |  Articles  |  web.dev, CC BY 4.0 (web.dev live page footer: 'the content of this page is licensed under the Creative Commons Attribution 4.0 License'; cite the page, not the archived repo)."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-05
as_of: 2026-11-05
confidence: medium
untested: "No code was run for this note; only the fetched documentation pages were read."
category: coding-references
topic_area: "web-performance"
tags: ['web-vitals', 'ttfb', 'server']
sources:
  - id: S1
    title: "Time to First Byte (TTFB)  |  Articles  |  web.dev"
    publisher: Google (web.dev)
    url: https://web.dev/articles/ttfb
    accessed: 2026-11-05
    license: "CC BY 4.0 (web.dev live page footer: 'the content of this page is licensed under the Creative Commons Attribution 4.0 License'; cite the page, not the archived repo)"
  - id: S2
    title: "Optimize Time to First Byte  |  Articles  |  web.dev"
    publisher: Google (web.dev)
    url: https://web.dev/articles/optimize-ttfb
    accessed: 2026-11-05
    license: "CC BY 4.0 (web.dev live page footer: 'the content of this page is licensed under the Creative Commons Attribution 4.0 License'; cite the page, not the archived repo)"
---
# Time to First Byte (TTFB)

**Answer:** TTFB is the time from the start of navigation until the first byte of the server's response arrives. It is a good signal that a web server is slow to respond. (S1)

## Details

- For page navigations, TTFB comes before every other meaningful loading metric. (S1)
- In browser timing terms it runs from `startTime` to `responseStart`, and it adds up phases such as redirects, service worker startup, and DNS lookup. (S1)
- 103 Early Hints responses complicate what counts as the "first byte"; web.dev explains how Chrome now treats them. (S1)

## Thresholds

- A rough target is 0.8 seconds or less. (S2)
- A slow TTFB pushes back every metric that follows it. (S2)
- TTFB is not a Core Web Vital, so missing its "good" mark is acceptable as long as it does not hurt the metrics that do count. (S2)
- A server-rendered page with less client-side work can have a higher TTFB yet better FCP and LCP than a fully client-rendered one. (S2)

## Claims
- id: C1
  claim: TTFB adds up several request phases, such as redirects and DNS lookup.
  source: S1
  evidence: "TTFB is the sum of the following request phases"
- id: C2
  claim: TTFB is startTime to responseStart.
  source: S1
  evidence: "TTFB measures the elapsed time between startTime and responseStart."
- id: C3
  claim: Aim for 0.8 seconds or less.
  source: S2
  evidence: "most sites should strive to have a TTFB of 0.8 seconds or less."
- id: C4
  claim: TTFB is not a Core Web Vital.
  source: S2
  evidence: "TTFB is not a Core Web Vitals metric"

## Sources
- [S1] Time to First Byte (TTFB)  |  Articles  |  web.dev. Google (web.dev). https://web.dev/articles/ttfb . License: CC BY 4.0 (web.dev live page footer: 'the content of this page is licensed under the Creative Commons Attribution 4.0 License'; cite the page, not the archived repo). Accessed 2026-11-05.
- [S2] Optimize Time to First Byte  |  Articles  |  web.dev. Google (web.dev). https://web.dev/articles/optimize-ttfb . License: CC BY 4.0 (web.dev live page footer: 'the content of this page is licensed under the Creative Commons Attribution 4.0 License'; cite the page, not the archived repo). Accessed 2026-11-05.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).