SDK vs API: Simple Guide for Developers

APIs (Application Programming Interfaces) and SDKs (Software Development Kits) are vital components of modern software development. APIs enable applications to communicate and exchange data, while SDKs typically provide a comprehensive toolchain, libraries, and documentation to build features as robust as possible, or even an entire application. This guide will go over the differences, examples, and how APIs and SDKs can work together to make it easier, faster, and more efficient for developers and businesses to innovate.

What is an API?

API stands for Application Programming Interface, which is a set of rules, endpoints, and definitions that enable different software components to interact.

Analogy: An API is similar to a clerk at the library counter. The clerk helps you communicate with the library's database. The clerk took your request, found or updated the book you needed, and gave you the results of your request without having to work with the library's database directly. An API does the same thing: it allows applications to talk to a system to request or send data without needing to access or understand what the ticketing or data collection system is doing internally.

How an API Works

1. Request: The client application sends a request to the API endpoint.

2. Processing: The server processes this request according to predefined rules and logic.

3. Response: The API sends back a structured response to the client.

Types of APIs

• REST API: Based on HTTP and returns JSON, this is the most common type of API used when building on the web.

• SOAP API: Depends on XML and is very rigid in terms of how the two parties communicate.

• GraphQL: An API that allows a client to ask for exactly the information or data that it needs.

• WebSocket API: An API that allows real-time, two-way communication.

How Do Developers Use APIs?

• Getting live weather data from a weather API.

• Pausing and processing a payment from the Stripe API.

• Embedding Google Maps into an application.

• Allowing microservices to communicate in a distributed app.

What is an SDK?

An SDK (Software Development Kit) is a set of tools, libraries, code samples, documentation, and debuggers designed to help developers create software for a specific platform or service. An SDK does more than just allow you to communicate with a service; it equips you, as a developer, with everything you need to build, test, and integrate applications in an organized and efficient manner.

Analogy: An SDK is like a complete developer’s toolbox. It contains the tools (libraries, frameworks), the instructions (documentation), and the ready-made parts (code samples) required to assemble and fine-tune your software.

How Does an SDK Work?

1. Function Call: The client (your application) uses the SDK’s built-in functions to request specific operations.

2. Processing & Abstraction: The SDK handles the complexities behind the scenes-such as API calls, authentication, and data formatting-so developers don’t have to manage them manually.

3. Data Exchange: The SDK communicates with the server, retrieves or sends the required data, and returns it to the client in a ready-to-use format.

   

An SDK generally consists of:

• APIs (for communication)

• Libraries (pre-written functions to save time)

• Documentation (how to use the tools)

• Sample Code (code that's ready to use)

• Debugging Tools (tools for debugging)

Types of SDKs:

• Platform SDKs: Hardware & Software examples of SDKs; building on a specified OS (Android SDK, iOS SDK).

• Service SDKs: Apps that leverage another service (AWS SDK, Firebase SDK).

• Hardware SDKs: Application-specific to certain hardware (VR headset).

How Do Developers Use SDKs?

• Building mobile apps using the Android SDK.

• Adding push notifications using the Firebase SDK.

• Building AI Apps using OpenCV SDK.

• Testing hardware devices using dedicated SDKs.

Real World Example

API Examples:

• Twitter API → Programmatically, fetch and post tweets.

• Spotify API → Get the data from playlists and songs.

• PayPal API → Provide secure payment transactions online.

SDK Examples:

• Android SDK → Create Android applications utilizing built-in components.

• AWS SDK → Access cloud services without having to manage HTTP requests and responses.

• Unity SDK → Create 2D/3D games while taking advantage of a physics and rendering engine.

Differences Between APIs and SDKs

Similarities of APIs and SDKs

• Both facilitate the development.

• Both are provided by a platform or service.

• Both can use one another; many SDK packages contain APIs.

API ​vs ​SDK: Which One Should You Use?

Use an API if:

• You just need to connect to a service.

• You want reduced integration load.

• You don't need to consider other tools besides communication.

Use an SDK if:

• You are building from scratch for a specific platform.

• You want pre-packaged everything - APIs, tools, and docs.

• You want to reduce development with packaged features.

Quick Demo - API vs SDK in Action

To make the difference between an API and an SDK concrete, let’s use the Open Weather Map service to build a tiny weather app.

Step 1 - Get Your API Key

• Visit https://openweathermap.org/api

• Create a free account if you don't already have one.

• Once signed in, under your profile, go to the API Keys section and copy your key.

Using the API (Raw HTTP Requests)

Now let's make a raw HTTP request to the API endpoint.

import requests

API_KEY = "your_api_key"  # Replace with your key from OpenWeatherMap
BASE_URL = "https://api.openweathermap.org/data/2.5/weather"

city = "London"
params = {
    "q": city,
    "appid": API_KEY,
    "units": "metric"  # Celsius
}

response = requests.get(BASE_URL, params=params)
data = response.json()

print(f"Temperature in {city}: {data['main']['temp']}°C")

Sample output

Temperature in London: 25.34°C

Here, the API will return you the unprocessed weather data in JSON format, and it's up to you how you would like to parse it and display it.

Using the SDK (Python Wrapper)

Open Weather Map has Python client libraries (SDKs) developed by the community that wrap these raw requests into easy-to-use methods. We will be using the pyowm package.

Run this in your terminal

# Install the SDK first: pip install pyowm
from pyowm import OWM

API_KEY = "your_api_key"  # Same API key from OpenWeatherMap
owm = OWM(API_KEY)
mgr = owm.weather_manager()

observation = mgr.weather_at_place("London,GB")
weather = observation.weather

print(weather.temperature('celsius')['temp'], weather.humidity, weather.detailed_status)

Sample output

19 65% broken clouds

In this case, the SDK can handle the following for us:

• Authenticate with your api key

• Send requests

• Parse the JSON

• Offer readable methods and properties

Therefore, less boilerplate and cleaner code than just calling the API directly.

How to Test Your APIs Without Writing Any Code or Touching an SDK

In this blog, we’re talking about the debate between SDKs vs APIs, right? We use both APIs and SDKs in our projects. Let’s say you want to test your APIs how do you check whether they are working fine or not? We manually write the test cases and verify them using assertions, right?

That’s fine for small projects, but what if there are so many APIs? How do you test them all? And what about the edge cases for the APIs?

Why worry when Keploy is here for API testing? Keploy provides you with a platform to create API test cases without writing any code or interacting with any SDKs. You heard it right the Keploy API Testing platform gives you API test cases that work for your application, including edge case scenarios too.

Curious about how it works? All you have to provide is:

1. cURL commands or a Postman collection

2. An OpenAPI schema

3. Your application URL (localhost also works)

Keploy will automatically create your API test cases and verify the test cases by running them against your application. In the end, you’ll have test cases that work for your application, and you can also run API testing in your CI/CD pipeline.

So, why wait? Go to app.keploy.io to create your test cases. Trust me, you will definitely like it.

Best Practices for Working with APIs

• Read the documentation thoroughly.

• Use environment variables for your API/token keys.

• Implement error handling in case there are any failures.

• Follow the rate limits so you do not get blocked.

Best Practices for Working with SDKs

• Use the latest version of the SDK; it will be up to date, and bug/security fixes will be included.

• Ensure the SDK supports your platform.

• Use the sample code to help speed up the development time.

• Understand the APIs that are included in order to better utilize the SDK.

Conclusion

To summarize, SDKs and APIs are two key components of contemporary software development and they represent distinct aspects of the process. APIs are all about communication; how things are provisioned and advertised, whereas SDKs include everything you need to build applications with as little friction as possible.

Generally, the question is about whether you need a basic way to connect two things, or whether you need the complete 'building blocks' to build your application. In reality, most successful projects utilize both APIs to integrate different services and SDKs to harness and expedite development, reuse assets, and leverage turnkey resources.

FAQs

1. Can I use an API and not use an SDK?

   Yes, you can just make the HTTP requests directly to the API without using an SDK.

2. Can I use an SDK and not use an API?

   Very rarely, most SDKs also have APIs, and they are designed to be used together!

3. Which is easier to learn API or SDK?

   APIs will usually be easier to learn because SDKs contain a lot more elements.

4. Do SDKs cost money?

   Most SDKs are free to use, but may require a subscription to the API if they are attached to any paid service.

5. Are SDKs platform-specific?

   Yes, generally, there are platform specifics for example, the Android SDK only works for Android apps.