APIs vs SDKs in Questions and Answers

Posted on by Julia Poltavets

In software development, API and SDK are the two things that get mixed up very often. Both are used to integrate third-party software, both provide pre-built components and sometimes it may seem that you need to choose between using an API or an SDK in building your app. Even when you browse QuickBlox developer documentation, you will find references to APIs and SDKs.

While APIs and SDKs are somewhat related, they are different in the way they are implemented. In order to clear the confusion between these two concepts, we decided to do a little research on how APIs and SDKs work and how they can be used in application development. We will try to answer the most frequent questions that may arise in connection with APIs and SDKs and help you decide whether an API or an SDK will be an optimal choice for your project.

1. What are APIs and SDKs?

Let’s start with the abbreviations. API stands for Application Programming Interface. SDK stands for Software Development Kit. Both APIs and SDKs are intended to include a software component built by a third party in your own product, but in each case a different approach is used.

2. What is the main purpose of APIs and SDKs?

If we can use a household analogy, an SDK is an IKEA table set, while an API is a drawing of a table or a YouTube tutorial on making a table. When you buy a table from IKEA, you need to assemble it at home using the included hardware but you are going to get exactly the table that IKEA designed. It is not going to be too hard, as all parts are made to come together tightly and you will have as many nuts and bolts as needed to assemble the table. IKEA also includes wrenches and screwdrivers that fit the hardware. You cannot, however, do too much about the size and design.

That’s SDK for you. When a software development company releases an SDK, it gives you a sort of an “assembly kit” where all components have been carefully developed and tested to work together. You will get an entire development environment with all integrations already set up as well as reusable code samples. A quality SDK usually also includes the documentation on how to set up the environment and build the app using the provided tools.

With an SDK, you are getting a complete functional component that you can set up really quickly and with little development effort. Using SDKs is the solution of choice for building client applications, as they include the full functionality as well as the tools to implement it. For example, with our iOS SDK you can create a mobile messenger app for iOS devices in a relatively short time.

Now, let’s look at the APIs. If we again use our table-making example, an API is a DIY option. You can find a step-by-step instruction or a video tutorial on building a table and then let your imagination run free. The basic rule is that a table should have four legs and a top, but you are free to choose how tall the legs are going to be and whether the top should be oval or rectangular. You will procure your own materials and tools and only use the tutorial for reference.

This is how APIs work. In fact, they are a set of rules and standards that you should follow to integrate a third-party service. They provide an interface to it allowing to reach the remote server and perform operations designed by the third party, but you need to set up the integration on your own. You will be free to choose the type of tools you are using in the process, however, integrating an API takes more effort. You will need to set up your own data mapping rules, authentication procedures, synchronization and logging scenarios, and a lot more.

3. What do APIs and SDKs contain?

An API usually consists of a number of methods that enable communication between your software and a third-party service. Calling a method using the strictly defined set of mandatory or optional parameters may change the value or return some data to the UI of your app. For example, QuickBlox API contains the Retrieve messages method allowing to retrieve messages from a particular dialog filtering them by a number of parameters, if needed.

SDKs, in their turn, contain a complete package of development tools designed to create a particular function. An SDK allows setting up the entire development framework to build the app or a functional component. Sometimes, an SDK contains one or more APIs enabling communication with third-party servers and fetching data from them.

For example, among its development tools, QuickBlox offers its Android SDK that you can use to build a messenger app for Android devices. It includes the corresponding code samples, the instructions on setting up the development environment and using the framework, as well as lots of other useful tools.

4. What are the main highlights of APIs and SDKs?

The table below contains a side-by-side comparison of APIs and SDKs based on our development experience. We use QuickBlox API and SDK as examples in this comparison.


Integration Time

Usually longer development time that may result in higher costs

Significant time-savings (about 1000+ man-hours per app) allowing to reduce the costs and time-to-market

Data Model

Designed to use standard HTTP protocols and return JSON payloads in response to HTTP requests

Due to the predefined classes that reflect the API data model, there is no need to write boilerplate code


Can be either written from scratch or set up using the preferred library/framework

SDKs usually sit on top of reliable and tested network libraries (or platform default), therefore, there is no need to develop networking layer


Full control over threads and concurrency. May be useful when performance and optimization are critical

Standard async and sync calls, very straightforward in terms of usage


No limitations, any storage option can be used

Standard caching & storage using best practices specific to a particular platform


APIs allow putting additional levels of security, using custom encryption etc.

Best practices are used which fits 99% of use cases

Maintenance & Migration

The development team is responsible for the migration to new versions of API and data migration

SDKs have inherent backward compatibility and mechanisms performing data migration in the related storage


Developers can pick the libraries or frameworks that are going to be used and have control over their versions. Alternatively, the integration can be set up with no dependencies

Most SDKs are built on top of popular, reliable and tested open-source libraries. In exceptional cases, dependencies may have conflicts


The developers are responsible for the whole architecture and have to write all of the code

SDKs require less coding as they are designed to simplify integration for a specific platform

5. What to choose – an API or an SDK?

In view of what we have found out about APIs and SDKs, we recommend that you choose according to your particular situation. If you have time and resources to set up your own integration, choose an API. If you want a quick solution with most of the preliminary work done, choose an SDK.

Besides, as we mentioned already, APIs are the tool to build server-side solutions, that is, if your goal lies in that area, use an API. SDKs, in their turn, are intended to develop client-side solutions and should be selected in such cases.

We hope we could throw some light on the “API vs SDK” issue and help your business make a better-informed choice. If you need more information about QuickBlox APIs and SDKs, contact our team for a detailed consultation. Our experts will gladly help you find the best solution for your messenger function or app.