What is Header Bidding?
Header bidding is a technique that lets publishers collect bids from several demand partners at the same time, before calling the ad server, so those bids compete with the ad server's own demand for each impression.
Also known as: pre-bidding
How it works
The name comes from where the code first lived: in the <head> section of a web page. Prebid's documentation describes the basic flow for a display ad in six steps (Prebid):
- The page starts loading.
- Header bidding code asks a set of demand partners for bids.
- The partners send their bids back.
- The ad server is called, with some or all of those bids attached.
- The ad server weighs every eligible ad, including the header bids.
- The ad server picks a winner for each ad unit, which may or may not be a header bid.
For the ad server to see those bids, ad operations teams create line items that match bid prices, and the header bidding code passes key-values (small labels such as a price bucket) that line up with them. If the two do not match, header bid winners can drop out of the final auction without anyone noticing.
Why it matters
Why did header bidding catch on?
Before header bidding, many publishers used a waterfall: the ad server called demand sources one after another in a fixed order, and a buyer further down the list never got a chance to outbid one higher up. Header bidding lets those partners compete at the same moment. Prebid's documentation notes that more competitive, more transparent auctions can increase revenue, and that publishers gain visibility into a process that ad servers historically kept as a black box (Prebid).
What are the trade-offs?
Header bidding is not free of cost. The ad call waits while bids arrive, which can slow pages and ad display, so publishers set timeouts: any bidder that does not answer in time is left out of that auction (Prebid). Each extra partner adds code, reporting and account IDs to maintain. Server-side setups move much of the work off the browser, and Google Ad Manager offers its own server-to-server alternative called Open Bidding, which it positions as easier to set up and lower in latency (Google Ad Manager Help).
Example
Example (illustrative)
A lifestyle website adds a header bidding wrapper with four demand partners and a short timeout. On each page view, the four partners bid at once and the best bids pass to the ad server, which compares them with a direct-sold sponsorship running that week. After a month, the site's team sees that one partner often times out, so it shortens that partner's list of ad units and tests the effect on page speed and revenue.
IncrementX perspective
Header bidding is a tool, and like most tools its value depends on how it is set up and looked after. A wrapper with too many partners, mismatched line items or stale floors can quietly cost money. IncrementX offers header bidding support covering wrapper setup support, demand partner integration and performance optimization, as part of its wider work representing publishers and connecting their inventory with demand. If you want a practitioner's checklist, see Header Bidding for Publishers: Is Yours Actually Working?, and read about Prebid for the open-source side.