The Ultimate Guide to API vs. SDK: What’s the Difference and How To Use Them

First, let’s figure out the terms we are using and why API vs SDK are even paired together.

What Is an API?

API (an acronym for Application Programming Interface) is an interface that enables intercommunication between two applications. It includes a standardized set of rules that define how this interaction can undergo, i.e., what kind of information to exchange, what actions to carry out, etc.

The first software sends out a standardized request, and the second responds in the manner described by the API.

Here’s a Metaphor To Explain How an API Works

Imagine you want to watch the Succession finale on a Sunday evening. You reach for a TV remote, click the power button, and then choose the HBO channel.

In this metaphor, you are the software that wants to interact with other software (a TV) and uses a specific interface (a TV remote). It defines the rules by which you can interact with each other and what responses you can get.

APIs are separated into four categories based on their availability and function.

• Public APIs can be used by any developer, be it an independent programmer or a business employee. It’s typically easily accessible and doesn’t require any specific authorization from you. 
• Partner API is offered by an owner business mainly to other companies and demands stronger authorization, often involving signing contracts. As a result, parties receive the rights and licenses to access the necessary data through partner APIs. It’s mainly used for a business-to-business data transfer with a secure network — for example, to share customer data with someone outside a company. 
• Private API can also be referred to as an internal API. It is used to transfer information within a company. Some examples of its usage include passing data from the front end to the back end or exchanging sensitive data between different departments.
• Composite API is the API that has more than a single request that it’s able to process. It’s a sequence of requests that are put together and sent out at the same time. 

There are multiple approaches to an API’s architecture and the ways it is built (REST and gRPC, to name a few), but the core concept and functionality stay the same.

Since we are discussing API vs. SDK, let's see how an SDK's definition compares to API.

What Is an SDK?

An SDK, i.e., Software Development Kit, is a pack of various tools that can be used to build software for a particular platform, like Microsoft Windows or Java. An SDK is comprised of relevant programming languages, compilers, runtime environments, documentation, debuggers, and even samples of code that carry out specific functions.

For example, Android’s SDK even has the standard Android buttons you can put in your app.

Such kits can become quite large, and the popular ones are often updated with even more features and tools for software developers. Moreover, SDKs commonly include APIs. For example, Android SDK contains multiple APIs for other services and all the necessary elements to create an API for your own product.

Thus, if an API is a TV remote, an SDK is a box with all the parts and schemas that you need to build a TV.

You could say that posing the question as "API vs SDK" is a false dichotomy: you need both to create a new app, and the former is actually included in the latter. The disambiguation of "API vs. SDK" comes from the fact that they both involve a second technical agent, a platform, or software that you want to work with. 

I would suggest replacing vs. in API vs. SDK for and, but the SEO gods would not allow me.

Now, let’s talk about the use cases for these instruments. As mentioned above, SDKs and APIs are almost ubiquitous in software development, but what are they actually used for?

When Do We Need To Use an API vs. SDK?

The question “when to use an SDK” has quite a simple answer.

Obviously, an SDK comes in handy when you want to create a product for a specific platform: an app for Android or IOS, Microsoft Windows programs, etc.

In theory, you could do it yourself completely from scratch and without any assistance, but using SDKs makes the software development process faster, simpler, and more accessible. It’s extremely rare to not use an SDK in software development.

APIs are used when you need another app to respond to a specific request under a certain scenario, such as sending a specific set of data, registering a user, carrying out a transaction, etc.

APIs are also quite common and are often used in the development of software that entails user authorization, monetary transactions, analysis of data from various sources, messaging, and so on.

Let’s say you want to develop an app that lets people on vacation rent seaboats nearby. You can use Android SDK to help you build the app itself and the API from Google to let people log into it with their Gmail accounts (once again, proving that you don't need to choose between API and SDK). You can also add PayPal API to let people pay for the boats.

Now that we’ve thoroughly reviewed these tools, let’s learn what are the noticeable distinctions between API and SDK.

The Differences Between SDKs and APIs

There are three main differences between API and SDK that we can point out. Some were brought up already, but here they are summarized:

Functions

As covered extensively above, APIs and SDKs solve different problems; one enables you to engage with other software while the other streamlines the development of your software. Thus, their main difference is in the goals they help to accomplish, but there are some more we can point out.

Size

A software development kit is quite a hefty collection of software-building tools that includes libraries, programming languages, documentation, lines of code samples, and guides to help create new software. All of this can be quite challenging to navigate.

Additionally, SDKs take up a lot of space on your computer; for example, Android SDK is typically around 50GB (depending on the version).

APIs, on the other hand, are extremely light and streamlined and only include the details needed to carry out their functions. They are very flexible and can be easily changed and adapted if needed.

Usage

The actual process of using these tools is also dissimilar.

When you want to employ an SDK, you need to download the packs from the respective provider. Oftentimes, SDKs are free, so you don’t need to pay before downloading the files.

On the other hand, most APIs from popular companies (social media, payment platforms) are commercial and require a signed contract to operate. The API itself looks like a set of codes that specifies the requests to the providers’ systems.

The Benefits of API vs. SDK

We mentioned repeatedly in this article that SDKs and APIs are used all over and for good reasons. Here are some of the benefits that API vs. SDK provides.

SDKs and APIs Save Time on Development

One of the main purposes behind inventing these tools in the first place was to cut the time needed for developing new apps and programs.

Software development kits gather all the necessary resources you need to build a product from scratch, so you don’t have to waste your time locating solutions and looking for the best options and ways to build what you want.

APIs eliminate the need to write a bunch of code every time you need to exchange information between two endpoints. Since they are standardized, you only need to choose an appropriate API and add it to your software - the job is done.

Thus, APIs and SDKs save hours of coding and problem-solving.

SDKs and APIs Provide Security

Of course, the security of the product will always be one of the top priorities for developers. Companies put a lot of resources into safeguarding their software from potential breaches and loopholes.

Trusted SDK and API providers commit to running regular security checks for the tools they offer. This lifts some part of the responsibility off developers’ shoulders and ensures there won’t be any data breaches when using their own product and interacting with other applications.

Moreover, there are many open-source APIs whose security can be verified by outside teams.

Most Commonly-Used APIs and SDKs Are Regularly Updated

The world of software development is, pardon my pun, constantly in development. New technical solutions that make developers more efficient appear all the time.

Popular SDKs and APIs, such as Java Developers Kit or Facebook’s Graph API, are updated every couple of months. SDK updates typically add new features and code samples, mitigate security breaches if there are any, etc.

All updates are aimed at giving you the best version of the product possible. Thus, you don’t have to revise your own code every couple of months to come up with better ways to authorize your users through Facebook; for example, this is done for you.

What Are the Challenges That Come With API vs. SDK?

The main challenge with APIs is their volatility; they are quite easy to change, and sometimes, an API provider can introduce updates that are incompatible with your software. This forces you to revise your product and troubleshoot the problems brought about by the update, which takes time and effort. Fortunately, such cases are not that common.

As for SDKs, the main challenge for developers is their sheer size. They can be enormous and include lots and lots of tools and examples, which sometimes can be frustrating if you just need to find a couple of functions for your product. Some providers solve this issue by offering different smaller packs designed for more specific needs.