What is header bidding?
Header bidding is a technique that lets publishers offer an ad impression to many SSPs and exchanges at the same time, before the page or app calls the publisher's ad server. All bids come back together, and the highest one competes with the publisher's direct deals. It replaced the older waterfall, where demand sources were asked one after another.
The name comes from the original setup: a JavaScript wrapper placed in the header of a web page.
How header bidding works
A user opens a page. A wrapper, most commonly the open-source Prebid.js, runs before the main ad call.
The wrapper sends bid requests to several demand partners, usually SSPs and ad exchanges, which pass them on to DSPs.
Partners respond within a set timeout, typically a fraction of a second. Late bids are dropped.
The top bids are passed to the publisher's ad server, which compares them with direct and other programmatic line items.
The highest-value option wins and the ad is served.
There are two main variants. Client-side header bidding runs the auction in the user's browser, which is transparent but can slow pages. Server-side header bidding moves the auction to a server, such as Prebid Server, which reduces page load and suits apps and CTV better, but can lower user match rates for buyers. Google's Open Bidding is a similar server-side approach that runs inside Google Ad Manager.
Why header bidding matters
For publishers, header bidding increases competition. Every impression gets real bids from multiple buyers instead of going to the first partner willing to pay a floor price, which generally raises yield.
For advertisers, it has three main effects:
Fairer access: DSPs see more inventory at the same time, rather than only what is left after higher-priority partners pass.
Duplicate requests: the same impression often reaches a DSP through several SSPs, which inflates bid volume and can lead buyers to bid against themselves.
First-price auctions: header bidding helped push the market to first-price auctions, so bid shading and smart bidding matter more.
These side effects are why buyers use supply path optimization to choose the cleanest, cheapest routes to the same inventory.
Header bidding vs waterfall
In a waterfall, the ad server called demand partners in a fixed priority order, each with a price floor, and stopped at the first one to fill. A higher bid further down the chain never got a chance. Header bidding asks all partners at once and lets the best price win, which is why it is now the industry norm on web inventory.
Header bidding with AdGeeks
As a buyer, AdGeeks works with header bidding from the demand side. On DV360 and Adform, our traders manage bids for first-price auctions, review which exchanges deliver the best inventory, and trim duplicate or low-quality supply paths so your budget goes to the impressions themselves, not to extra hops.
