Nice things we can't have

This page aims to be an exhaustive list of performance metrics we'd like to have, but can't because of privacy/security limitations. Feel free to add to it.

Why we need this list?

Hopefully in the future we can find a privacy-preserving solution for these, such as using private aggregation API for measurements and differential privacy for dimensions. Collecting the use cases would help us check if the shoe fits.

The list

The feature	Description	Why we can’t report it	Usage
Cross-origin redirects at start	LCP and navigation timing are affected by cross-origin redirects at the start of the response.	The final document should not be aware of the URLs that redirected to it	Measurement + redirect origins
Fine-grained memory usage		Cross-origin leak  (though this is perhaps Ok with COEP) + fingerprinting?	measurement
Some aspects of Network downlink			Dimension
DNS timing		Reveals things about the user’s configuration. Not the site’s data to opt-in to	Dimension
System load		New ancillary data	Dimension
Frame Presentation Time	More accurate representation of "pixels on screen"	visited links & ancillary data about machine	measurement
Battery/power level	Correlate between status of device/user and performance	very private info	dimension
Multiple redirects in RT	See this issue	current TAO semantics don't suffice	measurement
Various causes of entropy	e.g. extensions, system being busy, cold start	ancillary data	Dimension
Total page weight	Size of all resources, including cross-origin IFrames	Same-origin policy	measurement