# Response time (TTFB)

> Time to First Byte (TTFB) is the time from sending a request to receiving the first byte of the server's answer. It shows how fast the server and the network respond.

- **Check ID:** P1
- **Area:** [Performance](https://be1st.ai/glossary/performance)
- **Tool:** [SEO + Security + Performance](https://be1st.ai/tools/ssp-audit)
- **Page:** https://be1st.ai/glossary/performance/response-time-ttfb

## Why it matters

A slow TTFB slows down the entire page. If the server responds slowly, the user sees a white screen. Google uses loading speed as a ranking factor. According to web.dev, TTFB should be under 800 ms for a good rating. Every 100 ms of delay reduces conversions by approximately 1%.

## In practice

Amazon found that every 100 ms of delay cost them 1% in revenue. Google typically has a TTFB under 200 ms thanks to distributed servers and edge caching. If your e-shop responds in 2500 ms, the page takes 4-5 seconds to load and most visitors will leave.

## How be1st checks it

Time to First Byte (TTFB) measures the time from sending the HTTP request to receiving the first byte of the server response. web.dev recommends a value under 800 ms; the check passes under 1,000 ms (1,000-3,000 ms is a warning). When TTFB is not available, the total download time of the page is measured. TTFB is a fundamental metric that affects all subsequent metrics such as FCP and LCP. A slow server means the user is waiting before anything even starts rendering.

[SEO + Security + Performance](https://be1st.ai/tools/ssp-audit), Performance tab.

Every check ends as: Pass, Warning, Fail.

## Sources

- [Time to First Byte (TTFB)](https://web.dev/articles/ttfb) (web.dev)
- [Optimize Time to First Byte](https://web.dev/articles/optimize-ttfb) (web.dev)
- [Web Performance](https://developer.mozilla.org/en-US/docs/Web/Performance) (MDN Web Docs)

## Related terms

- [HTML size (performance)](https://be1st.ai/glossary/performance/html-size): HTML size is the weight of a page's HTML document in kilobytes. The browser has to download and parse all of it before it can show the page.
- [External resources](https://be1st.ai/glossary/performance/external-resources): External resources are the separate script and stylesheet files a page loads. Each one is another download that can delay rendering.
- [Inline CSS](https://be1st.ai/glossary/performance/inline-css): Inline CSS is styling written directly in the HTML, in `<style>` blocks or style attributes, instead of in a separate stylesheet file.
- [Inline JS](https://be1st.ai/glossary/performance/inline-js): Inline JavaScript is code written directly in the HTML inside `<script>` tags, instead of in a separate file the browser can cache.
- [Image optimization](https://be1st.ai/glossary/performance/image-optimization): Image optimization means serving images in the right size and format and loading the ones below the fold only when they are needed.
- [Total page weight](https://be1st.ai/glossary/performance/total-page-weight): Total page weight is the combined size of everything a page downloads: HTML, CSS, JavaScript, images and fonts.