What is TTFB by PLS
TTFB by PLS connects the server-side speed of Time to First Byte (TTFB) with how fast the page feels to users — measured as Perceived Load Speed (PLS).
TTFB is one of the earliest indicators of backend or CDN latency. PLS, on the other hand, reflects how soon users think the page is ready — based on content visibility, layout stability, and interactivity.
This lens shows you whether server speed is truly impacting perceived experience — or if users are happy even when the backend is a little slow.
Healthy TTFB by PLS sample
Should you worry
In a healthy chart:
Good PLS sessions correlate with fast (green) TTFB values.
The backend, CDN, and DNS layers are delivering responses quickly.
Perception matches reality — fast starts lead to fast-feeling pages.
This means the server is doing its part, and the frontend is carrying that momentum all the way through to the user experience.
Unhealthy TTFB by PLS sample
Things start to break when:
Good PLS, slow TTFB: Maybe your hero content is cached well at the edge, so users don’t notice server latency. But long term, this may hide problems in your origin setup or cache hit ratio.
Poor PLS, fast TTFB: The server is responding quickly, but the frontend is slow to render usable content — due to blocking resources, JS bloat, or layout shifts. Users feel frustrated despite good backend performance.
These mismatches help you pinpoint whether the bottleneck is server-side or in-browser — and whether perception masks or magnifies the real delay.
Resolving unhealthy TTFB by PLS
Go-to action plan to resolve an unhealthy TTFB by PLS:
Ask Uxi to analyze your TTFB by PLS values and suggest improvements.
Use Filters to isolate problem pages and identify backend or edge performance issues.
Simulate TTFB of the suspected lens to see if fixing it will resolve the TTFB by PLS. If yes, this is where the resolution focus should be.
Use an automated optimization tool like Navigation AI to improve your TTFB by PLS values.
Once you’ve improved TTFB, set an alert to be the first to know if it starts worsening again.
Try it yourself
Discover how your website performs with real user data.