Average TTFB Mobile

[Mik Dunne]

Hi, 

I have fixed the TTFB on both mobile and desktop for a site. The average has come down on Desktop, but the average seems to be taking much longer to come down on Mobile. 

We've seen a massive improvement in CRUX report, however the TTFB was fixed from Oct 2nd onwards and it's well under 1 second on both mobile and desktop, but still showing 1.3 seconds on Page Speed Insights. 

Is this normal? Does it take longer for the average come down on mobile? 

Thanks 

[Mik Dunne]

Here's a screenshot showing the improvement

I wonder is it because the average was so poor over many months before? However, I though it measured a 28 day period? 

Thanks

[Mik Dunne]

The screenshot above is Mobile only, here is Desktop 

[❄ Johannes Henkel]

The CrUX data in PSI is a 28 day period, in all cases.

It is also the same data that's in the CrUX API, so if you want to know the time interval, you can look at the CrUX API responses, particularly the part that's called CollectionPeriod.

E.g. (assumes API_KEY is set):

curl -s --request POST "https://chromeuxreport.googleapis.com/v1/records:queryRecord?key=$API_KEY"     --header 'Accept: application/json'     --header 'Content-Type: application/json'     --data '{"formFactor":"PHONE","origin":"https://www.example.com","metrics":["experimental_time_to_first_byte"]}'

Tutorial here: https://developer.chrome.com/docs/crux/guides/crux-api

You may also like looking at the crux history api, since it has weekly data points (28 day aggregation each).

https://developer.chrome.com/docs/crux/guides/history-api

This tool (not Google) uses the history API to make graphs such that underneath each bar it tells you the collection period.

https://tamethebots.com/tools/cwv-history

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[Mik Dunne]

Great, thanks for the links and data, pretty helpful!