Time to First Byte (TTFB)
Time to First Byte (TTFB) measures the duration from when a browser sends an HTTP request to when it receives the first byte of the server's response. It reflects the combined latency of network conditions, server processing time, and the time it takes for the server to begin sending data. Google considers a TTFB under 800 milliseconds to be "Good." High TTFB is often the root cause of poor LCP scores.
TTFB is influenced by server hardware and configuration, application code efficiency (including database query time), geographic distance between user and server, and CDN effectiveness. A slow TTFB is a foundational performance problem: even if all other page assets are optimized, a slow initial server response delays everything else. Caching, CDN edge delivery, and server-side optimization are the primary remedies.
Why it matters for SEO
TTFB is the foundational performance metric that sets the ceiling for all subsequent page loading times. A high TTFB delays LCP and all other rendering milestones, making it a critical factor to address before optimizing other performance aspects.
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