Everything you need to know about SDKs and APIs

SDKs and APIs are essential tools for modern software development. SDKs provide a toolkit that helps developers integrate their projects with existing software and hardware, while APIs define a set of protocols for software to communicate.

This article explains SDKs vs. APIs in detail, explaining the differences between them and their benefits, as well as covering what makes them essential to developers. It also includes information that will help you understand what you need when choosing an SDK or API for your project.

What is a software development kit (SDK)?

A software development kit (SDK) provides a toolkit that helps you to build your own software either on top of, or integrated with, another software or hardware platform. SDKs are produced by developers of operating systems, hardware platforms, programming languages, software, and applications, providing you with the tools and documentation to build software that integrates with their product. Each SDK is developed for use with a specific system: for example, the Windows and MacOS operating systems both have their own SDKs for building apps for their unique platforms.

SDKs provide a foundation and knowledge resource for building with a particular platform or product. The code and tools provided by SDKs, and the functionality of the products they integrate with, reduce the amount of code you have to write and put all of the information you need in one place, allowing you to focus on designing and implementing the unique aspects of your application. 

Because the software development kit is platform-specific, the toolkit varies depending on the platform. However, it typically includes code libraries, APIs, documentation, sample code, and tools that help in the development process.

For instance, if you are building a mobile app, you would use the SDK for iOS or Android. Each SDK provides you with all the necessary resources to build an app on that platform. This includes documentation, libraries to handle common tasks like networking and accessing specific device functionality such as GPS, and tools to help test and debug your code.

What is an application programming interface (API)?

An application programming interface (API) is a set of protocols and an interface for software to communicate. It allows different software components to share data and functionality by providing a standard for communication in combination with an endpoint for connecting. APIs simplify software development by allowing you to leverage the features of other software without needing to know the underlying architecture. 

APIs can be provided to local programs through the operating system, or over a network, and can be developed for in-house use or made publicly available as a service. Many online services provide APIs that allow you to integrate their products into your own. For example, you can integrate the Contentful® Composable Content Platform  with mobile and web applications to provide content like text, images, and videos by connecting to its APIs, removing the need for you to build your own content management system.

Popular APIs for adding functionality to apps include:

• Stripe for online payment processing.

• Shopify for ecommerce.

• Twilio for communication.

• Google Maps Platform for location services.

Application programming interfaces greatly extend what software developers can achieve when building apps. In-house APIs enforce a consistent way for your front and back ends to communicate, while online platforms that provide APIs add out-of-the-box functionality to your apps without you having to code it yourself. 

SDK vs. API: What are the differences?

SDKs and APIs are not the same thing, and their relationship is important to understand so that you can choose the right tools for your projects. The key differences between SDKs and APIs are their structure and components, use cases, and their purposes.

When to use SDK vs. API?

The decision to use an SDK or an API will depend on the requirements of your project, and what tools are provided by the technology you are integrating it with. For example, if you are building an application that needs access to data or processing provided by a third-party online service, you would use their API to enable the application to communicate with it. If, on the other hand, you are building an application that needs deeper integration or direct access to the features or data of a specific platform or technology (like accessing the camera or sensors on a phone or tablet, or using language-specific features), you would use the SDK for that platform.

Benefits of SDKs

Documentation

SDKs usually contain documentation and sample code for common use cases. This both teaches you how to use the SDKs and helps guide you during implementation, reducing the learning curve required to use new tools, and accelerating development with third-party technologies.

Standardization

The resources and tools provided by SDKs are developed to work together smoothly so that software developers can create their applications consistent with the platform’s guidelines and best practices. SDKs usually contain pre-built components such as code libraries and API integrations to provide a consistent foundation that reduces the amount of code you need to write yourself. 

By reducing the amount of code you need to write and maintain, software becomes more reliable, and can be brought to market in less time.

Abstraction

An SDK provides a layer of abstraction between you and the technology it is built for. For example, rather than you having to understand how to speak to a specific motion sensor in a phone (or multiple different types in different phones), mobile device SDKs mediate this communication. Thanks to the ability to hide internal complexities, developers can easily integrate that technology into their own products.

Contentful provides a JavaScript SDK that streamlines using our APIs, allowing you to integrate Contentful with your web application in minutes. We also provide the Experiences SDK that helps developers build their own bespoke applications and workflows for Contentful Studio.

Development ecosystem

As digital ecosystems and technology platforms grow in scope, so do the number of tools required to fully leverage them. SDKs (should) include everything you need to fully utilize a platform's features with as little effort as possible. 

For example, developing an app for an Apple device is no longer just about the app: you need to consider distributing the app on the App Store, keeping it up to date with newly released devices and operating systems, debugging, receiving customer feedback, analytics, marketing, and more. Apple’s SDK includes all of the tools and supporting material required to complete these tasks.

Benefits of APIs

Easy and secure data sharing

APIs allow different services to communicate with each other by calling them to exchange data and access functionality. They make it easy to provide integration between different software or platforms. APIs can implement authentication and authorization using user credentials or API keys, securing internal assets, or protecting paid-for API services.

If you’re building your own APIs, you can specify which data to share and how other services can access that data. Other services require minimal knowledge about your system — they only need to understand how to interact with your API. In this way, you limit other services’ access to your sensitive information. 

Productivity and efficiency

By assembling third-party services that expose their functionality through APIs, you can drastically cut development time. You can also reduce ongoing costs, as there is less code to maintain, and less infrastructure required to power your applications.

Standardization

APIs provide a set of agreed-upon standards that enables applications to make requests to get data and functionality. Standardization of communication provides a common language between developers, enabling collaboration between different teams working on front and back ends, as well as third-party services, so that all components can programmatically access and exchange data in a consistent way.

Composability

By facilitating communication through standardized means, APIs provide a high level of abstraction, providing a consistent interface regardless of the underlying storage or processing technologies. This aids reusability, allowing multiple teams or products to use the same service, rather than needing to implement it separately.

This also provides you with a huge amount of flexibility when developing applications using third-party services, as you don’t need to worry about compatibility with the technologies behind them. This allows you to compose applications, taking best-in-class products from different categories and combining them to achieve the overall functionality you require. For example, to create an app that lets you share pictures of your cat with friends, you could call an image API that resizes images (and adds pretty filters and effects) and then a communication API to send the photo in an email — eliminating the need for you to write your own image-handling and message-sending code.

Understanding the different types of APIs

While the functionality of APIs differs based on the underlying product, online APIs generally implement one of two popular technologies for communicating with them: REST and GraphQL. (This is in contrast to SDKs, which are more diverse in nature, and both the functionality they include and the means of communicating with them will largely depend on the technology they are developed for.) 

REST APIs

REST is an API architecture that emphasizes simple data formats, using URLs for identifying resources and using HTTP features for cache control, authentication, and content type negotiation. An API designed according to the principles of REST is called RESTful.

Anatomy of a REST API endpoint

A key concept in REST is a resource, which typically represents a single business object, such as a Customer or Product. REST uses the HTTP verbs for manipulating resources, which users can reference using a resource URL. For example, while the GET request returns the representation of the resource, the POST request creates a new resource.

GraphQL APIs

GraphQL is a query language and API architecture that creates a non-linear "graph" representation of your data, establishing relationships between objects and allowing you to query across multiple relationships. It is an alternative to REST APIs, but is not a competitor — they both serve different use cases.

A representation of a graph data structure

GraphQL is a powerful API tool that uses a single endpoint and can return data from any number of different data types, and even from third-party GraphQL APIs using schema stitching.

GraphQL diagram

Data returned from GraphQL APIs is typed, allowing for type safety across your frontend and backend codebase when combined with a typed language such as TypeScript.

Contentful lets you curate and publish content to your apps, websites, billboards, and even your AI

Modern software development depends on collaboration, both directly with other development teams, or indirectly using SDKs and APIs. 

Content drives the modern web, engaging users and encouraging interaction and sales for almost every type of application. Whether you need a full SDK vs. an API to build what you need, the Contentful® Composable Content Platform provides .NET,  iOS, and Android SDKs for integrating our headless CMS and content management tools with your own projects. We also provide powerful REST and GraphQL APIs for interacting with our platform, allowing your creative and development teams to collaborate and work together to give your users the best possible experience.

You can also extend Contentful using our App Framework SDK, to make Contentful truly yours and adapt it to your own workflows and requirements.

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