What Is The Difference Between Prebid.js VS Prebid Server

Header bidding revolutionized the digital advertising world for publishers, allowing them to sell ad inventory on multiple programmatic marketplace auctions in real time. In header bidding, publishers add a piece of code to the header of a web page and the code automatically generates requests for bids for the publisher’s inventory to Google and other ad exchanges. It replaced the traditional “waterfalling” technique and has helped publishers earn more revenue from demand partners.

Initially, publishers needed a technical team to implement and support header bidding. However, various open-source solutions have made setup and implementation easier for publishers, enabling more publishers to utilize header bidding technology on their website.

Today, there are various ways to implement header bidding, each with its own advantages and disadvantages. The leading open-source solutions for header bidding today are Prebid.js and Prebid Server. Although they are similar and not mutually exclusive, understanding each solution better can help you select the right one for you.

What is Prebid?

Prebid is the open-source wrapper technology used for header bidding. It is developed and supported by the global organization Prebig.org.

Each ad exchange has a unique configuration. As header bidding became more prevalent, publishers needed better tools to manage the bid request to each ad exchange. For example, they needed an effective way to select the highest bid return and return to the ad server with the best value. This need led to the creation of Prebid.org, a global organization managed by volunteers from the ad tech industry that aims to provide tools such as open-source wrappers that make it easier for publishers to manage header bidding.

Prebid Server

What is a prebid server?

A prebid server is a server-side header bidding solution. That means that instead of running auctions on a user’s browser, it runs them on a server.

A prebid server uses a server-side auction integration to make calls to the server. The server then calls all applicable bidders, selects the highest bid, serves the winning bid to the client, and passes it to the ad server. The ad server determines the winning bids, and if it is from the Prebid Server, the publisher’s website then serves the creative from the relevant demand partner to the publisher’s page.

How does a prebid server work?

Prebid Server streamlines the auction process in server-side auction integrations because it only makes one call to the server. The server then calls all the configured bidder adapters and serves the ad belonging to the bidder with the highest bid on the publisher’s website.

What are the advantages of using a prebid server?

Prebid server offers several key benefits including:

  • Reduced latency: When using a prebid server, the auction process runs on a server-side implementation rather than on a browser. That means that the content on the webpage can load independently, without being impacted by the ad auction. The load speed for the ads is faster which results in a better user experience.
  • Multiple demand partners can take part: Server-side header bidding makes it easier for publishers to add more bidders to their requests and earn more revenue from demand partners without affecting page latency.
  • Unified auctions: Managing and setting up ad units per wrapper can be challenging for publishers. A prebid server solves the problem, uniting server-side and client-side platforms and consolidating performance reports for all bidders/demand partners in one place.


What is a prebid.js?

Prebid.js is an open-source header bidding wrapper that simplifies header bidding on publisher websites and mobile apps. It includes 300+ demand partners and sources and 50 analytics adapters.

In the past, header bidding required a strong tech team, which made it inaccessible to many publishers. Prebid.js was created to break down the accessibility barrier with a simple, open-source solution that can be formatted to fit the revenue goals of each and every publisher.

Prebid.js is a core feature in the prebid ecosystem that offers an extensive collection of active adapters and an open tech layer where businesses can build their code. It utilizes client-side header bidding in auctions, which means that the auction code sits on the publisher’s website and is executed in the user’s browser instead of on a server.

The Prebid.js library includes:

  • Core wrapper code
  • Optional modules selected by the publisher
  • Adapters selected by the publisher

Prebid.js supports native, video, display, and a variety of other types of creatives for ads and lets publishers set up line items in Google Ad Manager. It also supports currency conversion, common ID systems, GDPR, and multiple ad servers.

How does prebid.js work?

Prebid.js is designed to be simple and only involves a few steps:

  1. Prebid.js library fetches bids and creatives from various partners and exchanges and passes price and information about the bids to the ad server’s on-page tag.
  2. The on-page tag passes it to the ad server as query string parameters, based on line items targeting the publisher’s bid parameters.
  3. The ad server returns a signal to Prebid.js pulling the winning creative from the library to the page.

What are the advantages of using prebid.js?

The main benefits of prebid.js are in ease of use. First and foremost, it’s faster and easier for the publisher to set up than a custom server solution. It also offers a higher cookie match rate and optimized configuration, which can improve publisher revenue.

The prebid.js header bidding wrapper does have disadvantages, for example, since it sends out multiple requests it can increase latency on the publisher’s website page. But when publishers don’t have the resources to manage their own server solution, the benefits of a managed solution like Prebid.js far outweigh any disadvantages.

Difference Between Prebid.js and Prebid Server

Prebid.js is a bidding wrapper technology that doesn’t require significant resources or technical expertise for setup or operation. It can help publishers find winning bids and increase their revenue.

A prebid server is a server-side header bidding solution that can be used to deliver a better user experience and reduce latency during an auction.

How to choose between Prebid.js or Prebid Server?

A prebid server is a great way to scale up demand and improve the user experience. That’s because with a prebid server, there is no limit to the number of server-side platforms (SSPs) a publisher can add, all of which are served a single request. And since it’s a server-side setup, the entire auction takes place on the server. Therefore, there are no problems with latency and other issues that can negatively impact the user experience while display or video ads are loading on a page.

With a Prebid.js wrapper, the auction is handled by the user’s browser. Since it sends multiple requests for bids to the ad server, it often slows page load time. But for publishers who don’t have an in-house technology team, Prebid.js can be a cost-effective, efficient solution that boosts revenue and doesn’t sap exorbitant organizational resources. Setup and implementation are simple and code can be added easily.

Which is better — a prebid server or a managed solution?

The decision between a prebid server or a managed solution like Prebid.js is really a function of the organizational resources a publisher has to invest. A prebid server has advantages in latency and user experience, but requires more expertise. Managed solutions like Prebid.js include all components in a wrapper, making them easier to use and manage.


Alisha is a Technology Writer and Marketing Manager at GeoEdge. Her writing focuses on current events in the AdTech ecosystem and cyberattacks served through the digital advertising supply chain. You can find Alisha on LinkedIn to discuss brand building and happenings in AdTech.

Malvertising, the practice of sprinkling malicious code into legitimate-looking ads is growing more sophisticated. GeoEdge’s holistic ad quality solution has you covered.


450+ Publishers & Platforms