Tech Report: Consider adding Back/forward cache (bfcache) Eligibility and Speculation Rules usage per Technology

[gilbertococchi]

Hello everyone, I wonder if there is any appetite to add new dimensions to appreciate UX achievements across Technologies.

One is the fact that by using a particular technology, Back/forward cache eligibility can be highly influenced.

With a simple check in the HTTP Archive queries like below it's possible to measure in time how many Origins are Eligible to Back/forward cache
Back/forward cache eligibility doesn't necessarily mean that a Back Forward navigation will go through Back/forward cache but it helps to identify whether there are major blockers like usage of Cache-Control: no-store, WebSocket, Unload and other blockers.

IF(lighthouse.audits['bf-cache'].details.items IS NULL, TRUE, FALSE) as bfcache_eligible

Similarly it could be also possible to measure how many Origins using a Technologies may be adding Speculation Rules (also here, adding a rule doesn't mean usage).
Example below about how to measure a presence of a Speculation Rules for Prefetch:

IF("SpeculationRulesAuthorPrefetchRule" IN (SELECT feature FROM UNNEST(features)), TRUE, FALSE) AS using_SpeculationRules_Prefetch

Looking forward to hear if others are also interested to see this kind of aspect.

There are CMSs that for legacy reasons are overusing Cache-Control: no-store for example, similarly 3P Chat Widgets that made their WebSocket implementation while others not etc.

[tunetheweb]

Lighthouse audits and other extra custom metrics were on the original roadmap for this report. Unfortunately we've had some people move off the project so no plans for these now. But keeping this over for if/when we do implement this.