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What Is an SDK and How Is It Different From APIs?

Braden Sidoti

Braden Sidoti

While an SDK and an API often work together in the software development process, they each serve a different function. Find out what that is here.

Modern software development typically involves using both software development kits (SDKs) and application programming interfaces (APIs). Even people with experience in the world of application development get tripped up over the fundamental difference between both sets of tools. Both help users improve the functionality of their applications quickly without having to construct something from the ground up. Let’s look at the core differences between SDKs vs. APIs and how they enhance the development experience.

What Is an SDK?

An SDK is often referred to as a dev kit. It’s a set of software-building tools made available from vendors. Developers usually rely on SDKs to build applications using a specific programming language targeted at a particular system or platform. An example of that would be the Windows SDK managed by Microsoft, which contains various frameworks for creating applications that run on Windows computers.

An SDK makes it easier for developers to create applications that follow a standardized pattern for a specific environment. Users download the kit and other components, like prebuilt application examples and instructions. SDKs give you a head-start on building, testing, and deploying a robust application.

What Is an API?

An API is a mechanism that helps two software modules communicate using specific protocols and definitions. It's a piece of software designed to fulfill a particular function. The weather app on your phone and the GPS application providing directions are examples of APIs.

The interface part of an API outlines the contract used between two applications attempting to speak to each other. Your API defines the request and response format used between the two. Developers can refer to the documentation for APIs to understand how they can set up requests and responses within applications built using an SDK.

How APIs Work

The architecture of your standard API typically consists of client and server functions. An application making a request is the client, while the one providing the response is the server. Your weather app calls the weather service database, asking for information, and the database provides information about the atmosphere in your specific location.

Below is an overview of different APIs:

  • SOAP: The Simple Object Access Protocol exchanges messages between clients and servers using an Extensible Markup Language (XML) format. The format became popular among developers in the past. The biggest drawback is the lack of flexibility in structuring requests and responses.
  • RPC: Remote procedure calls ask the client to execute a function, called a procedure, from a server. That server processes the output and sends it back to the client.
  • REST: Representational state transfer APIs define functions used by clients to access data from a server. Both clients and servers use HTTP to exchange information. REST APIs do not preserve data between client/server requests. Responses from servers are sent using plain data.
  • WebSocket: Instead of XML, WebSocket APIs rely on JavaScript Object Notation (JSON) to pass data back and forth. It’s a more modern approach that allows for two-way communication between clients and servers. The ability for servers to send callback messages to connected clients increases its efficiency versus REST APIs.

How a Software Development Kit Differs From an Application Programming Interface

The most significant difference between an SDK vs. an API is in how they enable development. Your SDK provides the building blocks you need to write new programs designed for specific platforms using your preferred programming language. There’s often at least one API included with most SDKs. Everything you need to construct a basic app comes with an SDK.

Developers can’t use APIs to build brand-new applications. However, they do allow applications to work together to enhance various aspects of your applications. For example, you can use an API to pull financial data and feed it into a dashboard featured on a website.

Common SDK Features

Let’s look at features that are often included when you download an SDK.

Integrated Development Environment

An integrated development environment (IDE) is used for creating various applications. The platform brings together numerous tools that developers rely on with one graphical user interface (GUI). Here’s a breakdown of the components of a typical IDE:

  • Source-code editor: Developers use this screen to write software code. A source-code editor often comes with options to highlight specific syntax, point out bugs, and auto-complete phrases in lines of code to help speed up development.
  • Build automation: This utility automates tasks used to set up local software builds for a developer. Build automation performs functions like packaging binary code and running automated tests.
  • Toolbar: An IDE toolbar resembles one found in a word processor. It organizes different components that developers rely on as they are writing code.

IDEs help enhance a software engineer’s productivity thanks to the way they standardize the configuration of various developer tools. Everything you need is available through one interface.

Debuggers

A debugger is a computer program that tests and finds bugs within a developer’s code. The debugger typically starts working as soon as you begin writing your code. As you compile your code and integrate it with other programming components, your debugger will highlight errors that keep the program from running correctly. Debuggers are essential to the development process, especially if you’re working on an application containing thousands of lines of code. You can also integrate unit testing to make things easier.

Code Samples

Code samples show developers how to implement different programming scenarios or concepts. They’re also helpful in showing you how to set up more complex architecture components, like a grid. Many SDKs provide you with complete applications and the source files needed to run the program.

Code Libraries

One of the main rules that programmers follow is "Don’t Repeat Yourself," or DRY. Code libraries help you stick by that principle by providing prewritten code that you can modify. These reusable blocks of code make it easy to save time while building projects or optimizing other pieces of your program. Another advantage of using tested code libraries is that they add stability to your application.

Documentation

The documentation that comes with SDKs provides you with instructions on using each component and integrating it with other systems.

APIs

APIs that come with SDKs contain libraries built using the platform’s core language. You can use your SDK to leverage APIs that add more capabilities to your program.

The Benefits of an SDK for Software Developers

SDKs make your job as a developer more straightforward by making it easier to pull different components together to construct an application. They make integrating standard processes easier and allow you to access pertinent information while coding. Many SDKs come with built-in support and documentation to help you leverage the program effectively.

Enhanced Control of User Interface and User Experience

An SDK gives you more control over the elements used to build your user interface. If a customer wants components laid out in a certain way, you can follow their requirements seamlessly with an SDK versus trying to use a basic code editor and disparate libraries. You’ll also have an easier time testing each screen element and ensuring that the users will be happy with the final product.

Quicker Time to Market

The code samples provided with SDKs allow you to create or expand the functionality of your applications quickly. You can leverage APIs and other libraries to quickly set up new components for your program. That makes the application easier to debug, test, and deploy in different environments before you release it for general use.

Broader Integration Options for Existing Tech Stack

With more vendors choosing to integrate APIs into their SDKs, there are more integration options available for developers. For example, if you have an application built using the .Net framework, you can still integrate the SDK with other frameworks to enhance the look of your UI.

Types of and Common Uses for Development Kits

While some SDKs enable connections between different tools, others help your applications run on specific devices and operating systems.

SDKs by Hardware

Many hardware providers make SDKs available to developers for programming technology like the Internet of Things (IoT) or programming robots. Having an SDK readily available for specific hardware makes it easier for developers to start their coding.

Open-Source SDKs

While most SDKs come from specific vendors, you can find open-source SDKs that allow developers to modify the underlying source code. However, there can be security risks associated with working with an unsupported platform.

Proprietary SDKs

In contrast to open-source SDKs, developers can’t access and modify proprietary source code. Instead, they must purchase a license permitting them to use proprietary code elements.

SDKs for Each Programming Language

Below are examples of SDKs available for different programming languages:

C#

JavaScript

Java

Python

Ruby

Do You Need Both an API and an SDK for Development?

It’s possible to build applications using an SDK without relying on APIs. However, working with APIs and SDKs together helps enhance the programming experience. It’s easier to construct platforms that meet your requirements. There are SDKs available for both Apple and Android developers who want to create mobile apps for those environments.

You don’t have to think of it as a choice between using either an SDK or an API. Remember, many SDKs come with preinstalled APIs. If you want to build a website that allows users to sign in through their Facebook account, an SDK makes that much easier.

You can automate user verification using the Facebook Graph API. That way, you, as the developer, don’t have to go through the trouble of figuring out how to generate tokens, inspect them, and determine which app the user is trying to connect through. The API makes the sign-in process for your app seamless.

Benefits of SDKs

SDKs help developers quickly add functionality to their applications and construct standard components. Typically, there’s no need to integrate an SDK with other elements. If you do, that might slow down your development process.

Most software engineers rely on SDKs to complete simple functions like allowing users to make mobile payments or setting up location services. Certain SDKs let you do more complex programming, like creating virtual reality (VR) and augmented reality (AR) programs.

When used correctly, SDKs help relieve the back-end burden of building software programs. You have a modular foundation to rely on that saves you much of the manual effort. Many of the apps created by software engineers contain a few features that serve a common purpose.

For example, a telemedicine app might offer chat features that let users reach out to medical professionals with questions or concerns. A mobile insurance app would contain features that allow users to check on a claim payment's status or print out a copy of their insurance card.

The efficiency provided by an SDK makes it easier for dev team members to work independently. It limits the number of common touchpoints, decreasing the risk of one person breaking another team member’s code during an update.

Adding APIs into the mix cuts down on lag time because of the research needed to figure out how to build a new capability. Working with an API means developers have to worry only about the necessary pieces that make their application work the way they want it to, eliminating the need to dive into how everything works under the surface.

Other SDK Considerations

Some SDKs have agreements to which you must provide consent before you are allowed to use the software. Vendors often make new versions of SDKs available for alpha or beta testing, meaning they are not yet publicly available. Those features you try out could undergo modifications or changes before the SDK’s general release. Certain features may fall under a license agreement, so you have to be careful that you do not develop a project that falls outside of its scope.

Read through all the documentation of any SDK you want to use and make sure there is nothing that conflicts with your desired usage. You can’t develop proprietary apps using an SDK with a General Public License. You should also look for any constraints around SDKs that come with a Lesser General Public License (LGPL) if you intend to build a project containing proprietary elements. Think about the ease of implementing security features like multifactor authentication.

Commercial vs. Open Source

Organizations also have to think about the cost of using an SDK. Many are tempted to use open-source SDKs because they’re free. However, your company could still end up paying if there’s a need for developers to spend hours getting up to speed on how the software functions. The cost of the time lost trying to figure out how an open-source SDK works could exceed what you might pay for a licensed version.

Commercial products do bring expenses associated with paying for licenses and integrating the components into current applications. However, you can turn to the vendor for support when you have questions. Paid SDKs tend to be more secure, which lowers the risk of your SDK becoming a gateway for a cyberattack.

You also have to think about the ease of using the SDK in your development shop. The goal of an SDK is to make coding easier. If you’re spending more time getting the application to function correctly than building software, there's a problem. Think carefully about implementing an open-source SDK. If your company has knowledgeable staff who are comfortable working with the product and bringing other developers along, you can succeed.

Usability is often the most significant advantage commercial products have over open-source SDKs. Even if you have developers who are capable of leveraging an open-source SDK, you have to think about who might be asked to maintain those applications if they end up moving on to another position or leaving the organization. How easy will it be to bring other software engineers up to speed on the SDK?

You should also look at the support provided by the SDK manufacturer. With open-source SDKs, there may be only online communities to turn to instead of a fully knowledgeable staff. If you have questions, there’s no guarantee that you’ll get timely answers or that there will be someone available who can help.

A Roundup of SDKs vs. APIs

SDKs provide developers with everything necessary to create or modify applications. Many come with prebuilt code that helps software engineers get started on their applications. APIs create connections between two applications and allow developers to expand the functionality available within a program.

It’s easier for developers to become more efficient by using SDKs and APIs together. When deciding on an SDK, look at whether you’re really saving by going with an open-source version when it comes to the cost, time, and effort. If your development team is unfamiliar with the platform, you could lose time and money trying to adapt.

Make sure that your SDK does not come with license restrictions that would impact your development. Explore the support that would be available to you or your dev team if you were to run into problems with your SDK.

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