Short answerHeader bidding lets several demand partners bid on the same impression at the same time, before the page calls its ad server. Instead of offering an impression to networks one after another (the waterfall), the site collects all bids at once, so the highest price wins. Prebid is the most widely used open-source framework for it.
When a publisher works with several ad partners, the order in which they get to bid matters a lot. Header bidding was created to fix that. This article explains how it works, what Prebid is and when it is worth the effort.
What is header bidding?
Header bidding is a technique in which a website asks several demand partners — SSPs and ad networks — for bids in parallel, usually from code in the page header, and then passes those bids to its ad server. The ad server compares them with its other demand and picks the best one.
The result: every partner competes for every impression, and the impression goes to whoever pays most at that moment.
Waterfall vs header bidding
In a waterfall setup, partners are called one after another in a fixed order. If the first partner does not fill the impression at a set price, it passes to the second, then the third. The problem is that a partner lower in the list might have paid more, but never got the chance.
Waterfall
Header bidding
Order
Sequential, fixed priority
Parallel, all at once
Who wins
First partner above its floor
Highest bid
Revenue
Often lower
Usually higher thanks to competition
Setup
Simple
More complex
Page speed
Fewer requests
More requests; needs a timeout
What is Prebid?
Prebid is an open-source project maintained by Prebid.org. Its two main parts are:
Prebid.js — a JavaScript library that runs header bidding in the visitor's browser. Each demand partner has an "adapter" that knows how to request its bids.
Prebid Server — the same auction run on a server, which reduces the work done in the browser and is used for apps and connected TV as well.
Prebid is free; publishers build a package with the adapters they need and configure it on their site.
How does a header bidding auction work?
The page loads Prebid and defines the ad units: sizes, formats and which partners bid on each.
Prebid sends bid requests to all partners at the same time.
Partners reply with bids within a timeout set by the publisher.
Prebid passes the best bids to the ad server, usually as key-values.
The ad server compares them with its own demand and serves the winner.
What should publishers consider?
Timeout. Waiting too long slows the page; cutting too short loses bids. Test it against your audience's typical connection speed.
Number of partners. Each adapter adds requests. More partners mean more competition, but returns diminish after a point.
Ad server setup. Prebid needs line items or rules in your ad server that match the bid prices it passes.
Page speed and Core Web Vitals. Load Prebid asynchronously and reserve space for ad slots to avoid layout shifts.
Consent. In the EU/EEA and the UK, Prebid modules pass consent from your CMP to the partners.
ads.txt. Every header bidding partner must be listed. See our ads.txt guide.
Is header bidding worth it for a small site?
It depends on your traffic and how many partners you work with. With one or two partners, a simple setup may earn almost as much with far less work. Header bidding pays off when several partners have real demand for your traffic and you can maintain the configuration. Our website monetization guide helps decide what to set up first, and monetizing a website beyond AdSense covers combining partners.
Header bidding and OpenRTB
Header bidding happens on the publisher side, often in the browser. Behind each adapter, the partner usually runs its own auction with buyers over OpenRTB. The two technologies complement each other.
Prebid with Wizads
Wizads supports Prebid for the banner format, so publishers who already run header bidding can add Wizads demand to their auction. Ask your manager for the configuration. The Wizads SSP also works with a simple script or a VAST tag if you do not use header bidding.
Frequently asked questions
Does header bidding replace my ad server?
No. Header bidding collects bids; the ad server still makes the final decision and delivers the ad.
Is client-side or server-side header bidding better?
Client-side gives partners more data from the browser; server-side is lighter for the page. Many publishers use a mix of both.
Can header bidding run video ads?
Yes, Prebid supports video ad units as well as banners. The formats a partner supports through Prebid depend on its adapter; Wizads supports Prebid for the banner format.
Wizads is an advertising network with its own DSP, SSP and ad server. Our team writes about programmatic advertising, website monetization and buying traffic.
