Chapter 2 of 8 · 4 checks · 2 min

Server response and TTFB

Every millisecond before the first byte delays everything after it. These checks keep the server, redirects and caching from eating the LCP budget.

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Keep Time to First Byte at 0.8 seconds or lessShould
Why it matters and how to check
Time to First Byte (TTFB) covers redirects, DNS, connection setup, TLS and the server's own response time. It is not a Core Web Vital, but it comes before LCP, so a slow TTFB makes a good LCP hard. As a rough guide, web.dev treats 0.8 seconds or less as good and more than 1.8 seconds as poor. The LCP guidance suggests TTFB should be roughly 40 percent of the total LCP time.
To verify, check the TTFB value in PageSpeed Insights field data, and measure from a few regions with curl. Look at time_starttransfer for your main templates, both on a cold request and a repeated one.
Example
Shell
curl -s -o /dev/null -w "ttfb=%{time_starttransfer}s total=%{time_total}s\n" https://your.site/
Remove redirect chains on entry URLsShould
Why it matters and how to check
Redirect time is part of TTFB. A visitor who lands on http://site.com and is sent to https://site.com and then to https://www.site.com/ pays for each hop before the page even starts loading. Links from ads, emails and social posts are the usual culprits.
To verify, run curl -sIL on the URLs you share most: the bare domain, the http version, campaign links and old paths. Each should reach the final page in at most one redirect, and internal links on your own pages should point at the final URL directly.
Example
Shell
curl -sIL http://your.site/pricing | grep -iE "^(HTTP|location)"
Serve cacheable pages from a CDN edge, without cache-busting parametersShould
Why it matters and how to check
The fastest response is one that never reaches your origin server. Pages that are the same for every visitor, such as marketing pages, docs and articles, can be served from CDN edge servers. The LCP guidance warns that unique URL parameters, such as tracking ids, can bypass the cache and send every visit back to the origin.
To verify, request the same page twice with curl and read the cache headers your CDN adds, such as age or a cache status header. The second request should be a hit. Then add a typical campaign parameter and confirm it is still a hit, or configure the CDN to ignore those parameters in the cache key.
Avoid
Setting cookies on every response for pages that are the same for all visitors
Flush the document head early or send 103 Early HintsNice to have
Why it matters and how to check
If the server needs time to build the page, it can still send something useful first. Some servers can flush the start of the HTML, including the <head> with stylesheet and preload links, before the body is ready. A 103 Early Hints response lets the browser start fetching critical resources while the server works, and it also counts as the first bytes for TTFB.
To verify, look at the Network panel timing for the document: with streaming, the browser should request CSS and fonts before the document finishes downloading. For Early Hints, curl -v should show a 103 response before the final 200.