What Is Header Bidding?
Header bidding is an advanced programmatic advertising technique that allows multiple demand sources to bid on an ad impression simultaneously, rather than sequentially through a waterfall. The core concept: instead of offering your impression to partners one at a time, you show it to all partners at once and let the highest bidder win.
How Header Bidding Works on the Web
Web header bidding runs JavaScript (typically Prebid.js) in the page header. It sends bid requests to all SSPs simultaneously via the browser, collects bids within a timeout window, and passes the highest bid to the ad server (usually GAM).
Client-Side vs Server-Side
Client-side runs in the browser with full cookie access but adds latency. Server-side (Prebid Server) reduces latency but loses cookie matching. Most publishers use a hybrid approach.
How In-App Bidding Differs
Mobile apps have no browser header. In-app bidding uses native SDKs compiled into the app binary. Mediation platforms (AppLovin MAX, Unity LevelPlay) manage the auction. A key advantage: ads are pre-cached in the background, so auction latency is invisible to users.
Critical Differences
- No cookies — mobile uses device advertising IDs (IDFA/GAID)
- SDK integration required vs simple JavaScript adapters
- Pre-caching eliminates user-facing latency
- App store review needed for SDK changes
Google Open Bidding
Google Open Bidding runs server-to-server through Google's infrastructure, works in both web and app, and simplifies integration by reducing SDK requirements. Trade-off: less transparency and Google takes a fee.
Yield Comparison
- Web bidding: 15-30% eCPM improvement over waterfall
- In-app bidding: 10-25% improvement over sequential mediation
RevenueFlex manages in-app bidding through Google Ad Manager for mobile publishers, configuring Open Bidding and hybrid setups for maximum yield.