A child in a shopping cart with his hands over his eyes and someone is holding two peppers in front of him, asking him to choose - API vs SDK concept.
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In modern software development, communication between multiple applications is essential to building a robust developer ecosystem, and in turn, a seamless digital experience for customers. Many companies already see the need to create a developer-facing business model, according to a recent Cloud Elements report, which found 55% of businesses use APIs as a revenue stream.

We've asked industry experts to explain what APIs and SDKs are, and when developers should use each.

Understanding APIs

An API is a way for developers to integrate ready-made functionality from another application into the software they're building programmatically. Lars Knoll, CTO of Qt Company, said developers "usually use a large set of different APIs to create their programs, which enables the encapsulation and reuse of other people’s work."

Knoll isn't alone in touting the benefits of APIs for efficient software development. Russ Danner, VP of products at Crafter Software, believes applications that "make data and functionality available as API(s) are more scalable, reusable and thus much more valuable because they are more flexible and can be leveraged by many other applications for any number of use cases." They’re often used as the building blocks to form a more complex microservices architecture to enable digital transformation in modern businesses.

With the rise of the Internet of Things (IoT), the communication of these devices through the use of APIs is only going to grow. APIs have been enabling digital transformations for companies in a wide variety of sectors because they ease the integration of third-party systems.

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What Is an SDK?

An SDK is what Knoll calls a "complete one-stop solution" for creating applications. It’s usually a package developers can install to assist with the development of new software. An SDK package usually comes with the collection of tools and APIs developers need to integrate a particular function or use-case into an app.

Arpan Seth, an engineering manager at Twitter, further explained that an "SDK hides the internal and lower-level complexities and provides a simple high-level code layer." The abstraction of SDKs makes software development faster, as developers don't need to know how a system works, only how to interact with it effectively.

SDKs often go a step further than APIs by including additional libraries, documentation and code samples. This also reduces the difficulty and learning curve for developers to implement third-party functionality in their software.

Related Article: 24 Headless CMS That Should Be On Your Radar in 2019

API vs. SDK: When and Where to Use Them

Now that we've gotten a better idea of what these terms mean let's explore some use cases for APIs and SDKs specifically.

Use Case APIs

Danner suggests that headless CMSs are "a perfect example of how APIs act as a force-multiplier for innovation." A headless CMS serves content via APIs without a presentation layer. “This architecture is sometimes called ‘Content-as-a-Service’ or ‘Content as an API.’ APIs make it easier to support multi-channel content and a variety of multi-channel digital experiences," said Danner.

APIs are the key for CMSs to integrate with third-party marketing tools or other systems to create a full digital experience platform (DXP) within an organization. This open platform approach allows organizations to innovate by combining external vendors with internal systems to create an effective business management ecosystem.

Seth suggests that APIs are also often used to access application data from a back-end database or interact with hardware like a phone camera. Since APIs are just an interface for interacting with an application, they’re used in nearly every industry from automotive to banking. That’s why, in the digital age, APIs have value for nearly any organization.

Use Case SDKs

Likewise, Seth reveals an SDK can be used to integrate with "a remote server (for ex: Twitter/Stripe API), an operating system (MacOS, iOS, Android), [or] a hardware device." in the IoT landscape, SDKs are prominent for developing against devices and other embedded systems. From these use cases, you can see platform owners typically make SDKs available for developers to build software specifically targeting their own platforms. Along with accelerating development, SDKs can ensure developers use best-practices when creating software for these specific platforms, which reduces security risks for platform providers.

While SDKs and APIs are similar, Seth said to "consider an API as a wrapper around the complex system and the SDK as a mechanism to talk with this API layer" using standard underlying rules. SDKs go beyond an API and make integration with a service even more accessible for developers — and this should be a priority for software vendors. Either way, in today’s API economy, offering a developer-centric revenue model is essential for businesses to create a robust digital platform.