How Do Client-Side And Server-Side Header Bidding Setups Compare?

Decoding Client-Side Header Bidding

Client-side header bidding, also known as browser-side header bidding, takes place within the user’s web browser. When a webpage loads, the header-bidding JavaScript code residing in the webpage’s header is executed. This code sends bid requests to multiple demand partners concurrently. The demand partners then conduct their auctions and send their bid prices to the page header.

The code in the website header subsequently passes the highest bid value to the ad server, which then determines the final winning bid. Once the server receives the winning bid response, it compares it with other eligible server line items and selects the line item with the highest CPM rate. Finally, the server serves the ad to the user.

Advantages of Client-Side Header Bidding

1. Higher Revenue: Client-side header bidding provides publishers with greater transparency and control over demand partners, allowing them to add or remove partners at will. This open auction format often translates into higher Cost Per Mille (CPM) for publishers, as advertisers are willing to bid more for audiences they know more about.
2. Better Cookie Matching: Since bidding happens in the browser, publishers can synchronize cookies and identify relevant users for advertisers. This leads to targeted advertising and, in turn, more revenue for publishers. It also enhances the user experience as users do not see irrelevant ads.
3. Transparency and Control: Publishers have complete control and visibility over how the auction functions and selects winning bids, including direct access to bid and log-level data.

Limitations of Client-Side Header Bidding

1. Latency Issues: Running numerous real-time auctions requires significant processing power. As all the processing takes place on the user’s device in the web browser, this can lead to increased latency and slower page loads.
2. Browser Limitations: Browsers impose limits on how many concurrent bid requests can be sent to SSPs and how many scripts can function on the page. This effectively caps the number of demand partners that can participate in the auction.

Demystifying Server-Side Header Bidding

Server-side header bidding, also known as server-to-server (S2S) header bidding, is similar to client-side bidding, with one critical difference. Instead of the auction taking place in the user’s browser, it happens on a remote server.

In server-side header bidding, an ad request is sent to the ad server when a webpage loads. The ad server then sends the bid request to multiple demand partners. The server handles the bulk of the computational load, reducing the burden on the browser and allowing webpages to load more quickly.

Advantages of Server-Side Header Bidding

1. Reduced Latency: By offloading the computational load from the browser to the server, server-side header bidding significantly reduces page load times. This enhances user experience and can lead to higher ad viewability.
2. Scalability: Server-side header bidding allows publishers to add as many bidders to the auction as they want, without negatively impacting latency. This can increase the pool of potential bids and potentially increase publisher revenue.

Limitations of Server-Side Header Bidding

1. Lower Cookie Match Rates: Server-side header bidding has lower cookie match rates as the user data is filtered while syncing the publisher’s and server’s Data Management Platforms (DMPs). This can decrease CPMs and impact overall revenue.
2. Lack of Transparency: Server-side auctions are often referred to as “black boxes” as everything that happens between the initial request and the winning bid is opaque. This means publishers have limited access to auction logic and bid data.

The Showdown: Client-Side vs. Server-Side Header Bidding

While both client-side and server-side header bidding have their unique advantages and challenges, the choice between the two largely depends on the specific needs and priorities of the publisher.

If maximizing revenue is the primary concern, client-side header bidding, with its higher CPMs and better cookie matching, might be the optimal choice. However, if user experience and page load times are paramount, server-side header bidding, with its reduced latency and scalability, could be the best fit.

Embracing a Hybrid Approach

For publishers who don’t want to choose between client-side and server-side header bidding, a hybrid approach offers the best of both worlds. This involves running both client-side and server-side auctions concurrently, allowing the winning bid from both auctions to compete for the final ad impression.

Final Thoughts

As the programmatic advertising landscape continues to evolve, so too do the technologies and strategies publishers use to maximize their ad revenue. Whether it’s client-side, server-side, or a hybrid approach, header bidding provides publishers with the tools they need to effectively monetize their ad inventory. By understanding the unique advantages and challenges of each approach, publishers can make informed decisions that best align with their business goals and needs.