The report has one job: turn a number that moved into a thing somebody can change. That means the resource diff matters far more than the metric, and the deploy correlation matters more than either.
Key takeaways
Lead with the resource that changed, not the metric that moved.
Correlate to the deploy feed, and say plainly when nothing correlates.
Separate third-party regressions, because they are somebody else’s change.
Two numbers for a non-engineer: the slowest important page, and whether it is moving.
A monthly summary; alarms only for confirmed regressions.
What a regression message says
Four lines
/pricing is 1.7s slower. LCP median 3.9s, was 2.0–2.2s across the last 21 runs.
What changed:hero-q3.jpg is 1.4 MB. The image it replaced was 180 KB. Total page weight is up 1.2 MB.
When: first slow run 09:40 Wednesday. A release went out at 09:12.
Also: the page is now over its total-bytes budget for the first time.
Nine samples per run; the full resource diff is attached.
The second line is the one that gets acted on. Somebody reading “LCP median 3.9s” has to go and investigate; somebody reading “hero-q3.jpg is 1.4MB” already knows what to do and roughly how long it will take.
The resource diff
Fig 1. How a regression gets its explanation. Three of the four outcomes name something concrete; the fourth is honest that the cause is not in the page.
Database
App integration
Management
Analytics
Outside AWS
When nothing got bigger
Same resources, same sizes, slower page. That is a server-side or network change: an origin that is responding more slowly, a CDN cache hit rate that dropped, a database query behind the page that got worse. The resource list cannot see any of it.
The honest report says exactly that: “page weight and request count are unchanged; the server’s response time for the document is up 800ms.” That is a different team’s problem and pointing at it precisely is more useful than a vague slowdown.
When nothing correlates
A regression with no deploy near it is worth reporting as such. It is usually a content change through a CMS, which does not appear in a deploy feed, and “no release correlates; the change is in an image, which suggests a content edit” points somebody at the right system on the first try.
Two numbers for everybody else
Fig 2. The monthly summary. The first three boxes are the version that means something to somebody who does not work on the site.
Machine learning
Management
Analytics
The slowest important page and its direction over a quarter is the whole story for anybody who is not going to open a resource waterfall. It is two numbers, it is comparable across months because the profile never changes, and it answers the only question a non-engineer actually has, which is whether the site is getting better or worse.