Header bidding helps publishers bring more demand into competition for their inventory. Auctions can run in the browser, on a server or both, and the choice affects both revenue and page performance. Prebid Server moves bidding away from the browser and supports monetisation beyond the browser. For many publishers, that flexibility is now a bigger reason to consider it than changes to third-party cookies. Recent browser-level restrictions on ad tech vendors have also renewed interest in moving more of the auction off the device.
But moving auctions to a server doesn’t remove the need to optimise them. Here is what to consider before implementing or expanding Prebid Server.
What Is Prebid Server?
Prebid Server is an open-source solution for server-to-server bidding. It receives an auction request, contacts the configured demand partners and returns a response once the bids arrive or the timeout is reached. On the web, Prebid.js sends a single request to Prebid Server instead of calling every bidder directly from the browser.
Beyond the web, Prebid Server powers in-app, AMP and DOOH auctions. It is auction infrastructure, not a complete solution: you will also need integrations, demand partners and reporting around it.
What Are the Benefits of Prebid Server?
The most common benefit is a lighter browser load and faster pages. In client-side bidding, the browser talks to every demand partner, so each new bidder adds network requests and processing, which is especially noticeable on slower devices.
Server-side bidding moves much of that work to a server. Our own testing supports this: when we compared client-side, server-side and parallel bidding in a live publisher environment, server-side delivered the fastest page loads and noticeably better viewability, especially on desktop.
Server-side also lets you add demand without slowing the page down. Testing a new bidder doesn’t require a separate browser integration, so new partners are easier to try out and bring on board. Third, the infrastructure can serve several channels. The same setup that runs your web auctions can also support your apps and, for example, DOOH advertising, and bidder settings can be managed centrally even across multiple sites and environments.
You also run less third-party code on your pages. When bid requests go through a server, you have better control over what happens on the page and what data is passed to partners. This also makes your setup less exposed to browser changes.
Prebid Server for Mobile Apps: In-App Monetisation with Prebid Mobile
For app publishers, Prebid Server isn’t optional. Prebid Mobile uses an SDK in the app that connects to Prebid Server: the SDK runs on the device, but the auction happens on the server. You therefore need a Prebid Server endpoint, either hosted by you or provided by a partner.
Server-side header bidding has been one of Relevant Digital’s core areas of expertise since 2020, on the web and in apps alike. Through Relevant Yield, we have helped publishers monetise their apps with Prebid Mobile. WetterOnline, for example, saw an incremental uplift of over 10% after the integration. Results like this depend on how bidders are configured and optimised over time.
What Are the Challenges of Prebid Server?
Identity and consent need attention. Google’s April 2025 announcement kept Chrome’s existing approach to third-party cookie choice, but users’ privacy choices and browser differences remain. When the auction moves server-side, bidders may not get the same identifiers and signals as client-side. Check what data is available and permitted, how it reaches each partner and whether that affects bids. Moving to a server does not change your consent obligations. Before moving demand server-side, also check that the Prebid features and reporting you rely on work there too.
Then there are the costs. Engineering time, hosting or service fees and processing all grow with request volume, and a setup can win more bids without earning enough to cover them. Look at net revenue and the gap between auction wins and rendered impressions. Revenue per session or per ad request, together with fill rate, response times and user experience, tells you far more than CPM. A bidder that performs well in one market or format may add little elsewhere, so it is worth calling bidders only where they bring value.
Prebid Server Implementation: Build In-House or Use a Partner?
You can host Prebid Server yourself or work with a technology partner. The right choice depends on how much control you need and how much expertise and time your team can commit.
Hosting in-house gives you direct control over the infrastructure and custom development, which makes sense if you have specific requirements and the people to support them. But getting the server running is only the start. Prebid’s hosting guidance lists what comes with it, from configuration and privacy handling to monitoring, and someone also needs to own updates, capacity planning and incidents. If all that knowledge sits with one person, you risk continuity issues, so documentation and team backups are essential.
A partner like Relevant Digital takes on most of the implementation and maintenance work and gives your team tools for configuration and analysis. When comparing partners, look beyond the hosting fee. Ask which bidders, formats and features are supported, where the servers run, what reporting you get and who handles support. It is also worth agreeing up front how you could switch providers later. For a wider comparison, see our guide to building in-house versus buying ad tech solutions.
Client-Side vs. Server-Side Prebid: How to Test the Best Setup
No single setup works best for every publisher. In our test, traffic was split between client-side (25%), server-side (25%) and parallel bidding (50%) across desktop and mobile web, with SSPs including Adform, Equativ, Magnite, PubMatic and Xandr.
Parallel bidding delivered the best overall result, client-side came very close in revenue, and server-side earned slightly less but loaded pages fastest. The gap between the methods was much smaller than in our earlier tests. How big the speed gain is for you depends on server location, latency, bidder response times and configuration, so measure how quickly ads render, not just how fast the auction finishes.
The biggest differences were between SSPs. On desktop, some bid less often server-side, while on mobile some bid more. That is why it makes sense to evaluate each partner separately and, in a hybrid setup, run each bidder where it performs best. Start with a small share of traffic, use comparable test groups and check that the gains last beyond a short test period.
Parallel bidding, where the same bidder runs both client- and server-side, adds requests, so enable it only for partners where it brings a clear uplift. Read the full results in our article on how server-side, client-side and parallel bidding compare.
Manage and Optimise Prebid Server with Relevant Yield
Relevant Yield is built on the idea that publishers should be free to choose client-side, server-side or hybrid setups based on their own needs. HB Manager supports Prebid.js and Prebid Server out of the box at no extra cost. Its no-code UI lets ad ops and yield teams change supported settings and run experiments without developers, and HB Analytics shows the results.
That makes the practical questions easier to answer: Which bidders should run server-side? Does dropping client-side bidders speed up your pages? Is the extra revenue worth the extra requests?
Prebid Server is most valuable when it gives you more options and measurably improves how your inventory performs. Start with a clear goal, test, and keep revenue decisions in your own hands.
Talk to the Relevant Digital team about implementing or optimising your Prebid Server setup.