Glossary/Programmatic/Header bidding
What is header bidding and how does it work?
How header bidding works, why it replaced the waterfall, and the difference between client-side and server-side setups.
Written by Samhub with the help of AI·Updated 13 Oct 2026·3 min readHeader bidding lets several SSPs and exchanges bid on the same impression at the same time, before the publisher’s ad server makes its final decision.
How header bidding works
The page loads a wrapper
A script, often Prebid, in the page or on a server.
All partners bid at once
Each SSP returns its best bid within a time limit.
The best bid goes to the ad server
It competes with direct campaigns and other demand.
The winner is shown
The highest-value option wins the impression.
Header bidding vs the waterfall
In the old waterfall, partners were asked one at a time in a fixed order, so a higher bid further down was often never seen. Header bidding asks everyone at once, which raises competition and price.
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Client-side vs server-side
| Client-side | Server-side | |
|---|---|---|
| Auction runs in | The reader’s browser | A server |
| Page speed | Slower with many partners | Faster |
| Cookie matching | Better | Weaker |
CPM uplift at Stampen Media after activating first-party audiences with Samhub.
Frequently asked questions
The most used open-source header bidding wrapper, maintained by Prebid.org.
Enough for competition, often a handful, while keeping page speed and timeouts in check.
Usually, because more buyers compete for each impression.
Yes, audience segments can be passed to bidders with each request.
Related terms
The open-source header bidding tool.
The software publishers use to sell impressions.
An auction for every single impression.
The lowest price a publisher accepts for an impression.
Manages many ad networks in an app.
All demand competes in one auction.
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