What is PLS by TTFB
PLS by TTFB reveals how Time to First Byte (TTFB) influences Perceived Load Speed (PLS). It shows whether delays in receiving the first byte from the server affect how fast the page feels to load for real users.
PLS captures the moment a user feels the page is ready — based on visual completeness. TTFB, on the other hand, is a backend metric that measures how long it takes for the browser to receive the first response from the server after making a request.
While TTFB doesn’t account for what users see, it sets the stage for how quickly content can be displayed. A long TTFB often delays the start of rendering, increasing the time it takes for visible elements to appear — which slows perceived speed.
This breakdown helps you:
Detect if backend latency is harming perceived load performance
Separate visual rendering delays from server-side delays
Prioritize infrastructure or CDN improvements that affect PLS
Healthy PLS by TTFB sample
Should you worry
In a healthy experience, pageviews with fast TTFB tend to have fast PLS values. That means the server is responding quickly and enabling rendering to begin early — resulting in pages that feel fast.
If slow PLS is consistently tied to higher TTFB, users are likely waiting longer before anything starts to appear on screen. That initial delay adds friction — and users feel it.
This is especially problematic on landing pages, first visits, or during peak traffic when infrastructure bottlenecks surface.
Unhealthy PLS by TTFB sample
A cluster of slow PLS values linked to higher TTFB suggests that backend latency is slowing down the visual experience. This can result from server slowness, geo distance, or poor caching.
Even pages with lightweight content can feel slow if users wait too long for that first byte to arrive.
Resolving unhealthy PLS by TTFB
Go-to action plan to resolve an unhealthy PLS by TTFB:
Ask Uxi to analyze your PLS by TTFB and suggest improvements.
Use Filters to isolate slow TTFB ranges and check for backend or origin-related delays.
Simulate LCP of the suspected breakdown to see if fixing it will resolve the PLS by TTFB. If yes, this is where the resolution focus should be.
Use an automated optimization tool like Navigation AI to improve your PLS by TTFB.
Once you’ve improved PLS, set an alert to be the first to know if it starts worsening again.
Try it yourself
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