SDK versus API: What’s the difference?
13 July 2021

6 min read

IBM Cloud Education IBM Cloud Education
Learn about software development kits (SDKs) and application programming interfaces (APIs) and how they improve both software development cycles and the end-user experience (UX).

In modern software development, the SDK and API are two principal tools you’ll encounter. They share plenty in common, and sometimes there’s confusion around what they each do.

At their core, both the SDK and the API enable you to enhance the functionality of your application with relative ease. To deliver on the promise of either or both—and improve the experience both in-house and for end-users—it’s important to understand how both tools work on the backend, how they differ and how they contribute to the overall development process.

What is an SDK?

SDK stands for software development kit. Also known as a devkit, the SDK is a set of software-building tools for a specific platform, including the building blocks, debuggers and, often, a framework or group of code libraries such as a set of routines specific to an operating system (OS).

A typical SDK might include some or all of these resources in its set of tools:

  • Compiler: Translates from one programming language to the one in which you will work.
  • Code samples: Give a concrete example of an application or web page.
  • Code libraries (framework): Provide a shortcut with code sequences that programmers will use repeatedly.
  • Testing and analytics tools: Provide insight into how the application or product performs in testing and production environments.
  • Documentation: Gives developers instructions that they can refer to as they go.
  • Debuggers: Help teams spot errors in their code so they can push out code that works as expected.

Often, at least one API is also included in the SDK because without the API, applications can’t relay information and work together.

How an SDK works

SDKs provide a comprehensive collection of tools that enable software developers to build software applications faster and in a more standardized way.

Cloud-native mobile app development, for example, leverages Apple’s iOS SDKs or Google’s Android SDKs for that platform. For larger-scale applications, such as enterprise Software-as-a-Service (SaaS) and proprietary web and desktop software applications, Microsoft provides the commonly used, open-source .NET SDK.

The simplicity of an SDK is just as valuable as the tools in the kit. Here’s how it works:

  1. Purchase, download and install the “kit” for your platform (for example, premade parts, examples and instructions).
  2. Open and leverage any APIs and all the development tools you need to build a new application, beginning with the integrated development environment (IDE). This is the space where you will do the actual coding and where your compiler is.
  3. Use the instructions, documentation, code samples and testing tools to do the building, which gives you and your team a healthy head-start.
SDK use cases

SDKs are part and parcel of mobile app development. They have many use cases:

  • Programming language-specific SDKs like the JSON and Java Developer Kit (JDK) are used to develop programs in those languages in a streamlined, standardized way.
  • Analytics SDKs from Google and others provide data about user behaviors, paths and actions.
  • Monetization SDKs like Google, Facebook and others make it easy for developers to roll advertising out in their existing apps, with the goal of generating revenue.
SDK benefits

SDKS make developers’ jobs easier by providing these benefits:

  • Access to constituent parts and instructions for software development: A retail SDK, for example, that pulls in all the things you’d want in your app (for example, favorites, cart, save for later, checkout, etc.).
  • Faster and smoother integrations: SDKs simplify the standard processes needed and provide ready access to information needed.
  • Shorter development cycle, getting products deployed and into market more efficiently: Because an SDK is built to inform, equip and provide shortcuts to development, developers can focus on developing the product they’ve planned.
  • Built-in support and expertise: No need to search for answers or hire out to augment your team; SDKs come pre-loaded with expertise in the code already written and the support documentation included.
  • Cost control: All the listed benefits enable you to better adhere to an established budget during development and post-deployment.

Now let’s dive into how that intermediary—the API—works.

What is an API?

API stands for application programming interface. Whether working as a stand-alone solution or included within an SDK, an API facilitates communication between two platforms. It does this by allowing its proprietary software to be leveraged by third-party developers. The developers can then enable their own users to indirectly use the service or services provided by the API solution.

You can also think of an API as a kind of agreement between two parties. The API not only allows for on-demand information exchange. It stipulates how that information should be exchanged.

Because some APIs provide the interface directly, the terms “API” and “interface” are sometimes used interchangeably.

To break that down, an API can consist of two things:

  • Technical specifications and documentation: This information explains how you’ll need to integrate the API to use it effectively.
  • The interface itself: You can access it directly via keyword (in the case of a web API) or indirectly from a separate interface (in the case of a REST API).

A few of the popular APIs are:

  • Web APIs, which are used to reach web browsers and devices or as their own web services application.
  • SOAP APIs, which are a popular choice in cases of heightened data privacy and security.
  • Open APIs (or public APIs) and REST (or RESTful) APIs, which are a popular choice for ease of use and maximizing bandwidth.
  • JSON-RPC, a goto for cases where asynchronous server calls are needed.
  • Custom APIs, for maximum agility with all the moving parts of software development.
How an API works

APIs make smooth, efficient integrations between applications possible.

For example, let’s say you have a real estate application. Your users want to be able to search for available real estate inventory—a service your software already provides. Furthermore, your users want to search for inventory within a certain area—a certain school district, perhaps. The most logical solution is to integrate with an established service. Leveraging a geolocation API would enable your application’s end users to use that service to focus on particular inventory without any awareness that the geolocation application is separate.

From a technical standpoint, here’s what an API call entails:

  1. As the application user who needs to complete a task, you initiate the task from your app, creating a request.
  2. The API makes a call to the web server, relaying the request. The API knows where to send the request because it goes to the API endpoint, typically the URL of a server.
  3. The task is then executed by the third-party application, or database, providing the service.
API use cases

APIs make many of the digital tools we routinely use possible. Here are three of the many API use cases:

  • Map APIs are commonly used to customize a map on a web page or mobile application.
  • Payment APIs are often used by e-commerce companies so they can offer purchasing flexibility to customers, expanding their potential customer base as a result.
  • Weather APIs can enhance the user experience of sports apps, search engines, etc.
API benefits

APIs enhance both the development experience and the end-user experience doing the following:

  • Connecting disparate software applications for a stronger overall product offering.
  • Shortening the development cycle through automation.
  • Reducing resources that would otherwise need to be allocated for in-house work.
  • Improving brand recognition and trust.
  • Providing new services to end-users with maximum efficiency.
Do you have to choose between SDK and API?

No—in fact, as noted above, an SDK often contains at least one API. These two help you in different ways but can and do work together.

APIs, again, serve to define how different platforms work together. They facilitate interaction through specifications (protocols); and as facilitators, they serve as one of the tools in a complete kit.

SDKs are the complete kit. They go beyond facilitation (though they include it) to provide everything for building new software for a specific platform or programming language.

For a further breakdown on the relationship between SDKs and APIs, check out this video:

Challenges and how to address them

The overwhelming sentiment when it comes to leveraging SDKs and APIs is that they make developing software applications easier and more cost-effective. They’re about as common to developers as email and chat platforms are to any business team.

That being said, there are some notable challenges that come with using APIs and SDKs. One challenge involves security breaches. Patchwork software development can result in unintended loopholes that can potentially expose personal information of users. There have even been cases of rogue SDK developers shopping around (and sometimes successfully propagating) SDKs capable of fraudulent activity, unbeknownst to the programmers using them.

For this reason, it is key for teams of all sizes to vet their providers and keep security on their radar throughout the development cycle.

Another challenge specific to SDKs has been the frequency of updates. When a development house has to support multiple versions of an SDK, it can cause synchronicity issues between that SDK and any APIs and backend systems is uses. In order to avoid end-user issues and security breaches, DevOps teams need to keep a close eye on versioning.

Availability is top-of-mind for most development houses—but having control over those development tools is equally critical.

SDKs, APIs and IBM

Interested in speeding integration development by 300%, reducing costs by more than 33% and maintaining enhanced security, governance and availability? Explore IBM Cloud Pak® for Integration, built on the core capability of IBM API Connect®.

You may also find valuable information in these resources:

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