What is TTFB distribution
TTFB distribution lens shows how your server response times are distributed across all pageviews, broken into 200ms intervals. It reveals whether most users experience fast server responses — or if slow backend performance is more common than expected.
Time to First Byte (TTFB) is the time it takes for your server to begin sending data after a request. It’s often the first bottleneck in load performance.
Healthy TTFB distribution sample
Should you worry
A healthy TTFB distribution shows a left-skewed shape — most pageviews land in the fastest intervals. Bars should decrease steadily as TTFB increases.
If the P75 marker is within the green zone, your server response times are in good shape for 75% of sessions.
Unhealthy TTFB distribution sample
An unhealthy TTFB distribution may show bars climbing again past the 600ms or 800ms mark — indicating that too many users are waiting for the server to start responding.
Common causes include:
Backend logic delays (auth, database, personalization).
Lack of edge caching or CDN misconfiguration.
Slow redirects or geolocation-based routing.
Resolving unhealthy TTFB distribution
Go-to action plan to resolve an unhealthy TTFB distribution:
Ask Uxi to analyze your TTFB distribution values and suggest improvements.
Use Filters to narrow down issues by geography, device, or URL.
Simulate TTFB of the suspected lens to see if fixing it will resolve the TTFB distribution. If yes, this is where the resolution focus should be.
Use an automated optimization tool like Navigation AI to improve your TTFB distribution values.
Once you’ve improved TTFB, set an alert to be the first to know if it starts worsening again.
Try it yourself
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