TTFB (Time to First Byte)
Checks Time To First Byte — server response time. Target under 600ms.
What this check measures
Time from request to first response byte. Affects all downstream metrics (FCP, LCP). Over 600ms is flagged; over 1s is critical.
Why it matters
TTFB is the baseline — every other metric starts after TTFB. Slow TTFB makes good LCP impossible. CDNs and edge caching are the usual solutions.
How our audit detects it
Measure median TTFB over multiple requests. Report p75 value.
Typical findings
- error_outlineTTFB 1.2s — SSR without cache.
- error_outlineTTFB varies from 200ms to 2s — cold start on serverless.
How to fix
Cache SSR output at the edge. Use a CDN closer to users. Reduce DB queries per request. Consider moving from serverless to containers for heavy SSR.
Frequently asked questions
Does TTFB matter for SEO directly?expand_more
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Scan my siteRelated checks
LCP (Largest Contentful Paint)
Checks Largest Contentful Paint — how fast the main content appears. Target under 2.5s.
PerformanceCLS (Cumulative Layout Shift)
Checks Cumulative Layout Shift — how much the page jumps during load. Target under 0.1.
PerformanceINP (Interaction to Next Paint)
Checks Interaction to Next Paint — responsiveness to clicks/taps. Target under 200ms.
PerformanceFCP (First Contentful Paint)
Checks First Contentful Paint — when the first text or image appears. Target under 1.8s.