What is TTFB by on-page errors
TTFB by on-page errors shows how Time to First Byte (TTFB) varies depending on whether the session encountered any on-page errors during or after load.
While TTFB is primarily server-driven, a high correlation between slow TTFB and client-side errors may hint at deeper reliability or delivery issues — like server misconfigurations, broken routing, or failing edge logic.
Healthy TTFB by on-page errors sample
Should you worry
In a healthy setup:
"No errors" dominate with fast TTFB
Pages with on-page errors still show stable, acceptable TTFB values
There’s no correlation between delivery time and later rendering errors
This suggests that your origin and edge infrastructure are decoupled from error conditions — meaning the server responds predictably, regardless of client hiccups.
Unhealthy TTFB by on-page errors sample
When sessions with on-page errors show slower TTFB, that may indicate:
Initial delivery includes broken references — like failing JS bundles or fonts fetched from unstable origins
Server logic (like A/B testing, geolocation, or personalization) occasionally fails, slowing TTFB and degrading render stability
Redirect loops or edge misconfigurations delay the first byte and increase the chance of broken resources loading afterward
If TTFB is fine but errors still happen, the problem lies in post-delivery execution. But if slow TTFB and high error rates go hand in hand, you're likely facing deeper infrastructure issues.
Resolving unhealthy TTFB by on-page errors
Go-to action plan to resolve an unhealthy TTFB by on-page errors:
Ask Uxi to analyze your TTFB by on-page errors values and suggest improvements.
Use Filters to isolate slow TTFB sessions and correlate them with broken assets or JS error logs.
Simulate TTFB of the suspected lens to see if fixing it will resolve the TTFB by on-page errors. If yes, this is where the resolution focus should be.
Use an automated optimization tool like Navigation AI to improve your TTFB by on-page errors values.
Once you’ve improved TTFB, set an alert to be the first to know if it starts worsening again.
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