Technology
How header bidding changed the open web
For years, publishers sold display inventory through a waterfall: each demand partner was asked in turn, and the first to accept a floor price won the impression. It was simple, but it left money on the table, because a later partner might have paid more.
Header bidding flipped that model. The page asks every partner at once, collects the bids in the browser or on a server, and passes the best one to the ad server. Prices rose, and publishers finally saw what their inventory was worth in real time.
Prebid.js became the open-source standard for running these auctions. Each bidder ships an adapter that translates the page's ad units into its own request format, and a shared configuration controls timeouts, consent and user sync.
Server-side setups such as Ozone's go a step further: the browser sends one request, and the server fans it out to many SSPs. That keeps pages fast while still letting demand compete for every slot, from the leaderboard at the top to the MPUs beside the article.
This page is a test fixture. It exists so ad ops can check that each slot is mapped, that bids come back and that creatives render in the right size.