Header Bidding
Header bidding is a programmatic technique in which a publisher offers its inventory to multiple demand sources simultaneously, before calling its ad server, so that all buyers compete in a single unified auction rather than a sequential waterfall.
Key takeaways
- Header bidding lets multiple SSPs and exchanges bid on the same impression at the same time.
- It replaced the old 'waterfall,' where demand sources were called one after another by priority.
- It can run client-side (in the browser) or server-side (in the cloud) "” often both, in a hybrid setup.
- Prebid is the dominant open-source framework for running header-bidding auctions.
Why header bidding exists
Before header bidding, publishers ranked demand sources in a waterfall: the ad server offered the impression to the highest-priority partner first, then cascaded down until someone filled it. This left money on the table, because a lower-priority buyer might have paid more. Header bidding fixed that by soliciting bids from everyone at once and passing the winner into the ad server to compete fairly.
Client-side vs server-side
Client-side header bidding runs the auction in the user's browser, which gives buyers rich signals but adds page latency. Server-side header bidding moves the auction to the cloud, cutting latency and browser strain but reducing match rates and cookie visibility. Most large publishers run a hybrid of both.
Prebid and the ecosystem
Prebid.org maintains the leading open-source header-bidding stack: Prebid.js for browsers, Prebid Server for server-side, and Prebid SDK for apps. Its neutrality made it the default plumbing for publisher-controlled auctions and a key force in the industry's shift to first-price pricing.
| Replaces | The sequential ad-server waterfall |
|---|---|
| Two modes | Client-side (browser) and server-side (cloud) |
| Common framework | Prebid (Prebid.js / Prebid Server / Prebid SDK) |
| Side effect | Accelerated the move to first-price auctions |
Frequently asked questions
What problem does header bidding solve?
It stops publishers from underselling inventory. In the old waterfall, a high-value buyer lower in the priority stack never got a chance to bid; header bidding lets everyone compete simultaneously.
What is the difference between client-side and server-side header bidding?
Client-side runs the auction in the browser with more data but more latency; server-side runs it in the cloud with lower latency but reduced identity match. Hybrid setups combine both.
Is header bidding the same as RTB?
No. Header bidding is how a publisher organizes competition among demand sources; RTB is the per-impression auction those sources may use to source their bids.