One of the basic purposes of the seller’s scoreAd function is to ensure that PA-API candidates exceed the auction floor price. This check, in most cases, is a trivial function “if A < B then reject” and does not depend on any data from the seller's trusted keyval. However, in the current PA-API setup, even running this trivial check incurs meaningful network latency in order to fetch the seller’s trusted keyval.

We propose a new top-level function in the existing seller’s script called “prefilterAd()” which runs some filtering logic on buyers’ bids without data from the seller’s keyvals. Chrome would first evaluate all buyers' candidates against this lightweight function and only call the seller’s keyval with eligible bids (if at all).

This optimization would…
(1) Prevent the seller's trusted server call entirely in cases where no PA-API candidates beat the auction floor.
(2) Otherwise reduce the request and response payload sizes of the seller’s trusted keyval by removing candidates that could never win.