Server Side Header Bidding VS Client Side Header Bidding Explained

Client Side vs Server Side Header Bidding: The Definitive Guide (2023)

Server side header bidding and client-side header bidding are the two primary header bidding technologies. While both enable website owners to monetize their traffic, they provide distinct pros and cons. Knowing which one to use on your website, can improve your ad revenue and user experience.

What is Server-Side Header Bidding?

Server-side header bidding, also called server-to-server (S2S) header bidding, refers to a process where the header bidding auction takes place on an external server. Moving the ad auction to an ad server speeds up the page load process and provides an opportunity to connect with an unlimited number of ad exchanges, ad networks, and SSPs.

While client side header bidding enabled publishers to increase their advertising revenue by connecting to more advertising demand partners, it came with some drawbacks. The real-time auction that enabled the SSPs, ad networks, and ad exchanges to compete, ran in the user’s browser. This increased the amount of processing power required by the browser. As a result, page load speed dropped.

Server-side header bidding was created to tackle these two challenges that occur with client side header bidding. However, this technology also introduces some new challenges. There is less chance of a cookie being matched which the technology which results in lower ad revenue. In addition, S2S header bidding can provide less transparency since the auction takes place on an external server. To learn more about the basics of header bidding see our what is header bidding guide.

What Are The Benefits of Server Side Header Bidding?

One of the main benefits of server-to-server header bidding is that it allows for faster and more efficient ad decision-making, as the ad server does not have to wait for each DSP to respond before moving on to the next. This can lead to higher ad revenues for publishers and more successful ad campaigns for advertisers.

There are also several other benefits to server-to-server header bidding, including increased transparency, better control over the ad inventory, and improved ad fill rates, greater scalability and enhanced user experience. However, it can also be more technically complex to set up and manage than other forms of header bidding.

1. Faster ad decision-making and load speed: One of the main benefits of S2S header bidding is that it allows for faster ad decision-making. When the header bidding auction is moved from the client’s browser to the ad server, the browser has less work. As a result, the page load speed improves. This can lead to higher ad revenues for publishers and more successful ad campaigns for advertisers.

2. Increased transparency: It allows for greater transparency in the ad decision-making process, as all demand sources are able to bid on ad impressions simultaneously. This can help to ensure that the winning bid is chosen fairly and that all demand sources have an equal opportunity to bid on impressions.

3. Better control over ad inventory: Publishers using S2S header bidding have more control over their ad inventory, as they can set their own rules for how ad impressions are sold and at what price.

4. Improved ad fill rates: Server-side header bidding can lead to improved ad fill rates, as it allows for more demand sources to bid on ad impressions simultaneously. As a result, you can see improved ad fill rates. This can increase the likelihood of finding a winning bid for each ad impression, leading to fewer unsold impressions.

5. Greater scalability: While browsers limit the number of network connections allowed at one time, server-side header bidding lets publishers connect to an unlimited number of advertising demand partners.  Therefore, Server to server header bidding is more scalable than client-side header bidding.

6. Enhanced user experience for native video: Video ads require substantial processing power and generally slow down the page load time. Server-side header bidding can lead to a better user experience, as it can reduce the number of calls made to external servers and reduce the overall page load time. This can be especially important for publishers with a large volume of traffic or a global audience.

The Downsides Of Server-Side Header Bidding

1. Cookie Matching: When the real-time auction takes place in the user’s browser, advertisers can scan for cookies that identify the user. Since advertisers aim to match their ads to specific user profiles, they are willing to pay more when they can identify users. With server-side header bidding, much of the user’s data can’t be sent to the ad server. As a result, advertisers get a lower match rate and bid less for the publisher’s ad space.

CafeMedia ran a one-week test where it sold advertising inventory only through server-to-server header bidding on some of its sites. Page load speed increased 40 percent on average, but CafeMedia EVP Paul Bannister also said revenue declined nearly 30 percent.

2. Transparency: Since the real-time auction is now happening on an external server, publishers may have less insight into the auction process. In contrast, with client-side header bidding publishers can see which buyers are participating in the bidding process and who won. This process can become problematic when the bidding partner is also providing the server-side header bidding “black box” along with their own demand. Here there is a potential conflict of interest as the bidding partner is bidding to win in the auction and getting to decide who wins.

3. Technical complexity: Setting up and managing a S2S header bidding setup can be more technically complex than other forms of header bidding, such as client-side header bidding. This can be especially challenging for smaller publishers who may not have the resources or expertise to manage the setup.

For this reason, many top publishers have instead selected an established and demand agnostic header bidding company like Snigel.

What's The Difference Between Client-Side And Server-Side Header Bidding?

Client-side header bidding creates an ad auction within the user’s browser. In contrast, server-side header bidding creates an ad auction on an external server. As a result, server-side header bidding requires less processing power from the user’s browser and delivers faster page load times. In particular, users with older devices or a poor internet connection will find sites using server-side header bidding provide a smoother user experience.



Server-Side Header Bidding (S2S)Client-Side Header Bidding (C2S)
Lower latencyHigher latency
Unlimited SSPs, ad exchanges, ad networksMore advertising demand partners leads to more latency
Lower revenueMore revenue
Less transparencyMore transparency

How Does Server-Side Header Bidding Work?

In server side header bidding, the ad server sends a request to multiple demand-side platforms (DSPs) simultaneously, rather than requesting each DSP sequentially. The DSPs then respond with their bid prices, and the ad server chooses the winning bid and serves the ad.

  1. The user enters a URL
  2. The browser starts loading the page
  3. The header bidding JavaScript tag located between the tags of the page sends a request to the ad server hosted by an S2S header bidding company like Snigel
  4. The ad server sends out bid requests to SSPs and ad exchanges
  5. The highest bidder wins
  6. The winning creative is retrieved and rendered on the page

Is Open Bidding a S2S Header Bidding Solution?

Yes, Open Bidding is a S2S header bidding solution. It is a platform developed by Google that allows publishers to offer their ad inventory to multiple demand sources simultaneously, using a server-side header bidding setup.

With Open Bidding, publishers can manage their ad inventory and the header bidding process through the Google Ad Manager platform. Demand sources can bid on ad impressions in real-time through the Open Bidding API, and the winning bid is chosen by the ad server.

One of the main benefits of using Open Bidding is that it allows publishers to manage their header bidding process through a single platform, rather than having to manage multiple integrations with different demand sources. It also allows for faster ad decision-making and improved ad fill rates, as demand sources can bid on ad impressions simultaneously.

Which Is Better, Client-Side Or Server-Side Header Bidding?


Publishers can get the best of client-side header bidding and server-side header bidding by using a hybrid setup. In this setup, the best performing SSPs and ad exchanges are run on the client-side while the long list of advertising demand sources with lower performance compete on the server-side.

In general, S2S is best for demand partners with broad advertising goals like brand awareness where the bids are generally lower. C2S is best for demand partners that are using specific data like cookies and visitor demographics to target audiences and therefore bid more.

Hybrid header bidding can be used in combination with other tools like video ads.

Overall, hybrid header bidding lets publishers connect to more advertising demand sources while minimizing page load times and the amount of processing power required by the user’s browser.

It’s crucial that publishers customize their hybrid header bidding setup based on:

  • The SSPs and ad exchanges that perform the best for the site
  • The regional location (Geo) of users
  • The target page load speed for the site
  • A supply path optimization analysis for the bidders. This determines which method (server or client) is the most effective for a specific bidder

Snigel can help publishers find which header bidding configuration works best on their site. See how this worked for in our server-side header bidding case study. We use multivariate tests and extensive data analysis to maximize ad revenue and minimize page load times. Contact our ad ops experts here to learn more.

About the Author

Ben is one of Snigel's Co-CEO. He works on business development and marketing - spreading the word about how Snigel can help publishers supercharge their ad revenue.


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