SDK vs API: What’s the Difference and When to Use Each?

In this article, we’ve covered SDKs and APIs with practical examples. The article also includes the key differences between them and specific use cases for each.

An SDK, or software development kit is a set of pre-built developer toolboxes for writing and running platform-specific code, such as for Android, iOS, MacOS, or Windows. SDKs contain all the modules and tools (code libraries, APIs, debuggers, IDEs, emulators, interpreters, profilers, and compilers) to handle all the technical complexities so that you can focus on building app features.

You can use SDKs to build applications for a specific platform or an operating system. Plus, you’d normally find documentation, tutorials, sample code, and guides within the SDKs for integrating and using them. 

SDK Examples

• Android SDK — Provides tools and libraries for developing applications on the Android platform. The SDK Includes dev tools, such as emulators, debugging tools, and APIs for creating UI and handling device features.
• Amazon SDK — Enables developers to interact with Amazon Web Services (AWS) for cloud computing, storage, and various other services. Allows you to build and deploy scalable applications on the AWS infrastructure.
• Google Cloud SDK — Offers tools and libraries for managing and deploying applications on GCP, including computing, storage, and data analytics services.
• Stripe SDK — Allows you to integrate and streamline Stripe's payment processing capabilities into apps and provides tools for businesses to do secure transactions. Also, it helps implement features for handling payments, subscriptions, and other financial operations within apps.

APIs, or application programming interfaces, allow applications to interact and exchange data with external servers, microservices, third-party services, and internal components using API endpoints. Unlike SDKs, APIs may or may not be platform-agonistic. Using APIs is a preferred way for apps to communicate with servers without worrying about the underlying technical complexities and data integrity.

Instead of building everything from scratch, developers can use APIs from different services to add new features or extend the functions of their existing apps. These requests are typically authenticated using API keys issued by the API providers.

Or, you can also build your own APIs, host them on cloud servers, and use them to power your software. Many applications use the REST architecture, which allows them to do data transactions with servers using HTTP requests to specific URLs or API endpoints. Besides REST, other popular API protocols include GraphQL, SOAP, and gRPC.

Also Read: API Testing 101: Types, Tools, Benefits, and More

API Examples

• Google Maps API — Allows you to embed Google Maps functionality into applications, adding interactive maps, directions, and location data.
• GitHub API — Enables your apps to interact with GitHub for managing repos, branches, and pull requests. It also helps automate repository management and access public information.
• Okta API — Facilitates user authentication and authorization for applications for secure identity management. Plus, provides features for implementing Single Sign-On (SSO) and managing user access policies.
• Stripe API — Provides tools for processing online payments, managing subscriptions, and handling financial transactions. Businesses use this (and similar other APIs) to integrate payment processing capabilities into their websites and apps.
• Spotify API — Allows developers to access Spotify's music catalog and user data for building music-related apps.

Also Read: Top 30+ API Testing Questions

While both SDKs and APIs aim at streamlining software development, there are a few comparison aspects that make them suitable for different use cases:

Intended Purposes for Usage

SDKs provide several tools bundled for development purposes. They are made specifically to shorten the time required for the SDLC to complete, whether for building new apps and features or adding custom functions to apps. Gathering tools like compilers, profilers, libraries, and frameworks yourself would take a lot of effort, knowledge, and technical work. Moreover, ensuring compatibility between those tools needs to be taken care of. SDKs handle all these technicalities behind the scenes, bundling them into a package, allowing you to focus on building apps without worrying about the technical details. 

APIs, on the other hand, provide a standardized way for applications to communicate with external or internal services. They define how data is exchanged and what operations can be performed. The primary difference between SDKs and APIs lies in the way they are meant to be used.

Usage Requirements

As described, SDKs are specific to programming languages and platforms. For example, you can use the Android SDK that provides tools for building Android apps with Java or Kotlin. 

APIs, on the other hand, can be written, available, and used in one or multiple languages. For example, you can use the Stripe API to integrate payment processing functions for your online store. And you can use the API using Python, Nodejs, Ruby, Java, and others. 

Size and Complexity

SDKs are generally larger and available as bundled toolkits and often provide a higher level of abstraction to handle many underlying details, making them more complex than individual APIs. They may require more technical expertise for installation and usage. Moreover, SDKs are geared more towards including specific functionalities and use cases for platform-specific apps. 

APIs are generally more focused, allowing developers to integrate specific functionalities with relatively less code. Plus, they are simpler than SDKs, as they typically focus on a specific function or set of functions.

Example: An SDK is used to build something (like an app), while an API is used to integrate a specific functionality (like payment processing) into something that's already being built. Note that some SDKs may include their own APIs.

Here’s a table that summarizes the key differences between SDKs and APIs:

Let’s look at some use cases for using SDKs vs APIs:

When to Use SDKs

Here are some common use cases for SDKs:

• Mobile App Development — Mobile SDKs, such as Android or iOS SDKs equip you with tools to develop, debug, monitor, and optimize mobile apps.
• Cloud Computing —  These SDKs provide APIs and libraries to connect to cloud storage and services. Example: Google Cloud SDK, AWS SDK, Azure SDK
• IoT Development — These facilitate writing IoT applications that can interact with sensors for data collection and analysis. Example: AWS IoT Device SDKs
• Game Development — Gaming SDKs come with 3D graphics, audio, physics, AI, and networking libraries. Example: Unity SDK

When to Use APIs

Here are some common use cases for APIs:

• Database Access — Use APIs to retrieve data from databases and manipulate it for use in your apps. It works best for data management and processing.
• Request Handling — You can handle HTTP requests and responses using REST APIs as a communication channel between client and server for data.
• User Authentication — APIs can be used to authenticate users securely.
• Role-Based Access — Use APIs to implement role-based access control for permissions and security management.
• Social Media Integration — APIs can be used including social media login options and share buttons in your apps. They can help enable the use of social media bots.
• Content Streaming — API integration can be used for streaming video and audio content on web apps.
• Mapping and Location Services — Such APIs can be used to embed maps and location data into apps.
• Ecommerce Transactions — Payment APIs can be used to carry out financial transactions.
• Microservices — Using APIs, you can connect your apps to leverage smaller, independent services called microservices to expand functionalities for your apps.