5 min read

What are Ad APIs? The Definitive Guide for 2024

Sarah Wheeler
Sarah Wheeler
Updated on
October 21, 2021
Intro to Ad Serving

With worldwide ad spend increasing by 12.7% in 2020 and YoY global ad spend expected to grow by 7.2% in 2024 - much of this going straight to Facebook, Google, and Amazon - more and more companies are looking to build their own walled ad garden to capture this revenue as well. As developers determine how to build these platforms, the challenge is figuring out how to do it correctly and quickly.

Often, when companies launch an ad platform, they are expected to either build a robust platform from scratch, or resort to an imperfect client-side solution. However, both of these options are time-consuming and costly.

kevel build or buy

This article discusses another option: ad APIs, explaining them and showing how they enable you to launch an ad platform at a fraction of the time and cost as building it entirely yourself. Rather than build vs buy, it’s build vs build faster.

What are ad APIs, and who uses them?

The API industry is booming, with major tech players like Stripe and Twilio worth tens of billions. Such companies provide APIs, or Application Programming Interfaces, that give developers the tools to build complex systems without reinventing the wheel.

Instacart, for example, uses Stripe’s APIs to power its payments infrastructure. Sure, they could take a year to build this functionality from scratch (saving them Stripe’s fee), but why do that when you can get access in just days?

As TechCrunch reports, “For fast-moving developers building on a global-scale, APIs are no longer a stop-gap to the future -- they’re a critical part of their strategy.”

APIs for communications, payments, data, and more have become the industry standard. Ad APIs, however, are a relatively new technology with lots of promise.

Historically, companies like Facebook, Amazon, Etsy, etc. designed their own ad products in-house, taking years to build and millions of dollars to launch. Or, publishers have served ads using Google Ad Manager, a client-side solution with its own host of problems.

etsy ads

Neither of these approaches are ideal: building an ad product in-house is expensive and time-consuming, and “buying” a third-party ad server cedes flexibility and control.

This is where ad APIs enter the picture. Just as Twilio’s communication APIs facilitate easy integration of texting and calling into one’s app, ad APIs simplify building robust, high-revenue ad platforms in weeks, not years.

kevel build or buy

Ad APIs do this through providing the infrastructure for ad serving, targeting, and reporting. These systems are complex but commoditized, as it is no longer sensible for each individual publisher to design a pacing algorithm, frequency capping rules, click tracking, and so on. Ad APIs give publishers turnkey access to these building blocks, so they can build the exact ad platform they want in 90%+ less time than designing from scratch.

The beauty of ad APIs is they can integrate into anyone’s website/app, such as these companies who built ad platforms on top of Kevel's ad APIs:

  1. Mozilla - Pocket is a service built into Firefox that allows you to save and discover content for later viewing. Mozilla used ad APIs to launch sponsored articles in their Firefox browser in a privacy-safe way. They built this native advertising platform using ad APIs in a matter of weeks.

Mozilla sponsored listing

2. Atom tickets - Atom Tickets used ad APIs to implement native ads, enhancing and monetizing their browsing experience. Powered by ad APIs, these native ads instantaneously appear with organic site content.

Atom tickets example

The benefits of using ad APIs to build an in-house ad product

With companies like Facebook, Amazon, and Etsy building in-house ad platforms (and seeing billions in returns), it follows that others would follow suit. However, instead of building this product entirely from scratch, using APIs might make sense for a few reasons:

  1. Time to Market: Every day your platform isn’t live, you lose revenue. Building from scratch can take years. Ad APIs, on the other hand, can reduce that time by 90%, enabling you to launch in weeks.

build v. buy chart

  1. Engineering Resources: Instead of the 10+ engineers needed to build an ad platform, ad APIs allow you to build a full-featured platform with just 1-3 (without ad tech experience). Plus, you will need far fewer maintenance engineers to maintain and service the platform.

kevel build or buy

  1. Automation: With ad APIs, you can automatically create/update campaigns, ads, and more in bulk.
  2. Scalability: If your system can’t handle the ad request volume, you’ll see slow response times, high server costs, and crashing systems, all of which lead to lost revenue. By outsourcing this work to an ads API partner, whose business is handling scale, you can focus on building new features, not

kevel build or buy

  1. Customization: Any successful ad platform needs several features, and building each of them yourself is daunting (and time-consuming). You’ll want all these features sooner than later, and an ads API tool should provide turnkey access to most.


  1. Privacy-minded monetization: Privacy laws like the GDPR (EU), CCPA/CPRA (California), and LGPD (Brazil) are expanding globally. Violating these laws is a PR nightmare, and the GDPR alone could cost your company 4% of its yearly revenue. Instead of spending your time mitigating this risk, an ads API partner simplifies privacy compliance by researching, advising, and updating the system for you.
  2. Cost Savings: You'll need fewer engineers and won't have to pay for server costs as you scale.

kevel build or buy

Why use an ad API product over a JavaScript server?

Publishers have relied on third-party client-side tags or in-app SDKs to monetize their sites/apps for years. However, these tags slow down load times, often involve obtrusive banner ads, and can leak PII.

Server-side ad APIs are better alternatives to client-side ad serving, as there is:

  1. No ad blocking: Ad blocking tools identify major ad tech tags, preventing monetization of [36% of Europeans and 38% of North Americans] Programmatic ads and even direct-sold ads tags will get blocked. Alternatively, server-side ads pass by ad blockers undetected.

  1. No cookies: Any third-party script could drop cookies and tracking pixels unbeknownst to you - a violation of both user trust and privacy laws. These could harvest and sell user data, infringing on user privacy. Ad APIs, however, don’t use cookies, so there’s no risk of PII leakage.
  2. No malware: Malware can infiltrate ad tags, costing publishers nearly $1B per year. On the other hand, there are no malware risks with ad APIs.
  3. No obtrusive ads: While client-side ad tags don't necessitate a programmatic ad monetization strategy, they usually go hand-in-hand. Such ads stand out and are often placed awkwardly - leading to frustrated users and bad brand experiences. Using ad APIs instead allows you to insert beautiful native ads that blend in alongside your standard content. Below, WeTransfer uses ad APIs to monetize their homepage with seamless native ads.

WeTransfer example

A robust ads API solution offers all the infrastructure needs for your ad platform. At Kevel, for instance, our suite of APIs include the following:

  1. Reporting API: The reporting API can be used to pull reports by advertisers, campaign, etc. As a neutral third-party, they are a trustworthy, sharable source of data for your advertisers.

Reporting API

  1. Management API: This lets you create and manage advertisers, campaigns, ads, and more. You can use the Management API to build your own self-serve advertiser portal, whereby any changes they make would be pushed live.
  2. Ad Serving (Decision API): This enables you to make ad requests without using ad code. You send a JSON request and get a JSON response with details about the winning ad.


  1. UserDB API: The UserDB API allows you to upload user-level data to incorporate first-party data targeting into your campaigns.

The challenges of using an ads API product

Though we’ve discussed many reasons why ad APIs are optimal for building an ad platform, it might not be for you if:

  1. You don’t have any software engineers. APIs require engineering resources and technical knowledge. Generally integrations take a couple of weeks with 1-3 dedicated engineers.
  2. You don’t have any advertisers. Most companies using ad APIs build native ad platforms and have direct relationships with advertisers. Without demand, you may be better suited to a tag-based ad server like Google Ad Manager.

The top ad API infrastructure companies:

As the ad API industry is nascent, there is only one brand positioning itself as an ad API infrastructure: Kevel. With Kevel, brands can launch custom, full-featured ad servers in a fraction of the time and cost of trying to build it from scratch.

When to consider Kevel:
  • You want fast page/app load times, preferring server-side ad calls to JS-tags.
  • You want full customization of your ad units.
  • You want full flexibility and control of your ad business.
  • You want automatic campaign creation, management, and reporting.
  • You want a self-serve ad platform.
  • You have ad demand.
When to think twice:
  • You want a platform set up in hours.
  • You don't have engineering resources.
  • You want the ad server to provide programmatic demand.

kevel build or buy

How Kevel helps you build your own ad platform in just weeks

There are many ad servers out there, but only one API-first partner: Kevel. Kevel’s infrastructure tools make it easy to launch your own ad platform in just weeks, saving you resources, time, and money. Let us know if you’d like to learn more.

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