We’ve explored what we mean by APIs and why strong API documentation is important to software developers when choosing applications.

But there’s one more thing that really helps get apps over the line when it comes to implementation – and that’s good quality SDKs (software development kits).

So if you’re wondering:

  • What is a software development kit (SDK)?
  • How is an SDK different from an API?
  • Do SDKs have something to do with toolkits or devkits?

…then you’ve come to the right place.

Our friend James will explain what is an SDK, how they make integration cleaner and faster, why it’s an absolute necessity for companies to offer them and how to choose an SDK that works for you.

Read on for everything you need to know about SDKs.

Software development kits (SDKs) help developers build integrations with a company’s services fast. An SDK should provide a toolkit of components that third-party developers can drop into their own applications.

SDKs are usually designed for specific programming languages, frameworks, and platforms. To support different environments, you will need to offer a separate SDK for each one. For example, ClickSend provides ten different SDKs including most major languages – C#, PHP, Java, Node.js, and Python.

A streamlined SDK is often the difference between a smooth integration and a painful one. Being able to identify good toolkits will save you time and improve your software’s long-term maintainability. 

What makes up an SDK?

An SDK usually offers one or more of the following components:

  • Code libraries that provide pre-built objects and methods for interacting with the company’s systems using a particular programming language
  • Debugging tools that allow developers to test their integration against a development environment and diagnose any issues that occur
  • Compilation and build tools when the SDK is designed to work with compiled languages or physical hardware devices
  • Documentation that provides a reference for all the other components, as well as clear guides for getting started and lists of best practices

These parts form a toolkit that provides everything you need to integrate with the vendor’s service. You can start with the documentation, write code using the included snippets, then test and build your project – using an officially supported workflow.

SDKs are available for many different technologies, from hardware test kits to relatively simple wrappers around web APIs. The Android SDK comes with everything you need to author, test, and build Android apps. Docker’s SDKs help you build integrations with the popular containerization platform. ClickSend’s suite of SDKs lets you easily add communications APIs within your own code.

Why you need SDKs

SDKs help to simplify common development tasks – saving time and cutting costs. Choosing vendors that offer SDKs lets you integrate more quickly using an approach endorsed by the supplier. This shortens the development cycle and maximizes reliability.

SDKs are a holistic, convenient approach, as all the resources are included in one bundle. Verified code samples sit alongside the documentation showing you how to use them, making integration easier.

It also helps you to effectively debug any issues that occur. There’s less margin for error when you’re using library code produced specifically for integration. Instead of manually typing out API endpoints, use the features of your IDE to discover codebase entities that can be called alongside your own work.

Why companies should offer SDKs

Developer demand for SDKs is high and many teams will evaluate SDK availability and quality when selecting a new service provider. Developers don’t want to spend their time writing boilerplate code before they can perform basic interactions with a new SaaS product.

Companies that provide an SDK to integrate with their platform therefore have an advantage in attracting attention and making sales. Offering an SDK demonstrates a commitment to encouraging third-party development that helps to reinforce the quality of your service.

Building an SDK encourages you to approach your own platform from the perspective of an external developer. This can identify feature gaps and other opportunities to enhance your service, creating a virtuous cycle of improvement.

The act of publishing an SDK also requires you to produce documentation and getting started guides that support customers in understanding your platform’s capabilities. This can encourage a quick start and a positive first impression of your service. 

Companies can sometimes find it daunting to produce SDKs. For best results, you need to offer a solution for each of the major programming languages that your customers are likely to use. This could be challenging if you lack in-house experience with some of those environments. Fortunately, there are tools like Swagger that can automatically produce SDKs from OpenAPI specifications. This allows you to offer a comprehensive lineup of toolkits without manually writing each one.

SDKs vs. APIs

SDKs are often offered alongside application programming interfaces (APIs). An API provides a standardized interface for interacting with a particular service. They’re usually platform- and language-agnostic while SDKs are tied to specific environments.

SDKs often wrap a company’s existing API. They make the API easier to use in the context of a particular programming language. Developers don’t need to pay too much attention to the workings of the API, reducing the learning curve and encouraging adoption.

The ClickSend platform is a good example of how SDKs make integration easier. Here’s an example of how you could list all the contacts in your account as a PHP developer using manual API calls:

$listId = 100;

$client = new GuzzleHttp\Client([
    "headers" => [
     "Authorization" => "Basic YXBpLXVzZXJuYW1lOmFwaS1wYXNzd29yZA"

try {
    $contactsRequest = $client -> request(
catch (\Exception $ex) {
    // Something went wrong

$data = json_decode($contactsRequest -> getBody(), true);

if (!is_array($data)) {
    // Something went wrong

// Get the phone number of the first contact in the response

This code is verbose and relies on several hardcoded strings to assemble the request URL and access data in the response. As the API works with plain JSON, it’s difficult to map data back to a format that’s useful to your PHP application. You’re also responsible for manually encoding your API credentials and including them as a header with each request.

The ClickSend PHP SDK lets you transparently access the API using PHP function calls:

$listId = 100;
$page = 1;
$limit = 10;

$clicksendConfig = Clicksend\Configuration::getDefaultConfiguration()
    -> setUsername("YOUR_CLICKSEND_USERNAME")
    -> setPassword("YOUR_CLICKSEND_API_KEY");

$clicksendApiInstance = new Clicksend\Api\ContactApi(
    new GuzzleHttp\Client(),

try {
    $contacts = $clicksendApiInstance -> listsContactsByListIdGet($listId, $page, $limit);
catch (\Exception $ex) {
    // Something went wrong

The SDK makes the API much easier to consume within your code. You can use the provided objects and methods to perform complex API interactions without assembling URLs yourself. The SDK will also help mask any changes to the API in the future, providing a degree of future-proofing for your code.

There are use cases for both APIs and SDKs. APIs work across environments and sit atop standard data exchange formats. They’ll always be relevant as a way to communicate between two independent platforms with minimal constraints.

An SDK is a complete development toolkit, of which an API might be a component. SDKs make APIs easier to work with by wrapping their endpoints in environment-specific utility methods. This allows deeper integration with your code. The SDK also incorporates all the peripheral material for successful development, such as documentation and any required build tools.

Identifying a good SDK


A good SDK will have been purposefully designed to make specific tasks easier. You can assess it’s quality by checking whether it covers all the functions of the company’s API and has comprehensive documentation similar to ClickSend’s portal, which groups content by languages.

Screenshot of the ClickSend SDK library with C#, PHP, Java, NodeJS, Python and Perl devkits

Unclear or missing documentation can be a sign that the SDK isn’t regularly maintained or widely used. Making it harder to build and maintain your integration over the life of your system.

Coding standards

It’s also worth checking how closely the SDK aligns with the programming paradigms that are common to the target language. The best SDKs will mirror the prevailing standards (ie object-oriented or functional programming) and use modern language features. SDKs shouldn’t be overly bloated, though, as heavy packages could slow down your application and increase its bundle size. This is especially important for mobile applications and IoT solutions.


It’s important to analyze any SDK’s security before you use it. You could be unintentionally adding vulnerabilities to your codebase by adopting an SDK without auditing the source. Many organizations discovered this in late 2021 when the Log4j vulnerability was reported. This popular Java logging library was widely used across the ecosystem. It was often included in projects as a sub-dependency without the author’s knowledge. SDKs and apps that are still using an unpatched Log4j version continue to be targeted.


Finally, look at the vendor’s SDK versioning practices to check how long your integration will be supported for. Different companies will have their own policies for how long an SDK release is maintained. Some are proactive in keeping old versions protected with bug fixes while others quickly cease support as new programming language and framework updates are published.


An SDK provides platform-specific tools that help developers integrate their work with third-party services. Quality SDKs can be a distinguishing point for software vendors. They encourage integration by providing simple interfaces that can be called directly from existing code. A good SDK will feel like an extension of your programming language, with comprehensive documentation that leaves no doubt around how it should be used.

With SDKs providing so many advantages, it’s worth choosing a vendor that offers them each time you integrate with an external service. Choose our API for sending and receiving SMS, email, voice, and direct mail worldwide. We have a range of SDKs cover the majority of popular programming languages, making it easy to start adding cloud communications to your app.

Sign up to get started here.