What this measures
Writes a 256 KB response into the Cache API and reads it back, then deletes it. The times are cache put and match, not HTTP cache headers on the network.
How to read it
Start with the capability checker if a later page says an API is missing. Then run the workload that matches the question, instead of treating every page as one score.
What it cannot do
A missing API is not a broken computer. The troubleshooter is a reading of symptoms, not a remote diagnosis. The stress test still cannot show heat.
Questions
The capability check lists a missing API. What now?
Use the tools that do not need it. A missing API is not scored as zero.
Why is WebAssembly not much faster?
The loop is small. Call overhead can dominate. The page shows both rates so you can see that.
The troubleshooter did not name a part.
It should not. It points at the measurement that matches the symptom and at the limit of that measurement.