Header bidding is a mediation that consists of an auction that takes place (by default outside) of the ad server via the header of a web page.
When the page loads, the header script loads before anything else on the page and enables publishers to have simultaneous auctions with all bidder.
header bidding is also known as:
Header Bidding is an open auction over the publisher ad inventory and offers every ad opportunity to multiple bidders at the same time, significantly increasing competition and monetization.
Header bidding seeks to compete all demand sources, both direct sold and programmatic, simultaneously in a unified auction.
With header bidding, every impression is auctioned off to all demand partners simultaneously, before the publisher’s ad server is even called. Advertisers Advertisers (Ad buyers) using programmatic channels get to look at every single publisher’s impressions, not just those that went unsold in a traditional waterfall setup without header bidding.
Header bidding’s most important impact on publishers is the significant increase of revenue
Auction House that supports header bidding:
Header bidding documentation on divers network
Because the process happens in the loading of a webpage, this is possible to see the auction with a browser extension.
Example