APIs are mechanisms that enable two software components to communicate with each other using a set of definitions and protocols. For example, the weather bureau’s software system contains daily weather data. The weather app on your phone “talks” to this system via APIs and shows you daily weather updates on your phone.

API stands for Application Programming Interface. In the context of APIs, the word Application refers to any software with a distinct function. Interface can be thought of as a contract of service between two applications. This contract defines how the two communicate with each other using requests and responses. Their API documentation contains information on how developers are to structure those requests and responses.

REST stands for Representational State Transfer. REST defines a set of functions like GET, PUT, DELETE, etc. that clients can use to access server data. Clients and servers exchange data using HTTP.

The main feature of REST API is statelessness. Statelessness means that servers do not save client data between requests. Client requests to the server are similar to URLs you type in your browser to visit a website. The response from the server is plain data, without the typical graphical rendering of a web page.

A Web API or Web Service API is an application processing interface between a web server and web browser. All web services are APIs but not all APIs are web services. REST API is a special type of Web API that uses the standard architectural style explained above.

The different terms around APIs, like Java API or service APIs, exist because historically, APIs were created before the world wide web. Modern web APIs are REST APIs and the terms can be used interchangeably.

APIs are classified both according to their architecture and scope of use. We have already explored the main types of API architectures so let’s take a look at the scope of use.

API endpoints are the final touchpoints in the API communication system. These include server URLs, services, and other specific digital locations from where information is sent and received between systems. API endpoints are critical to enterprises for two main reasons: 

All APIs must be secured through proper authentication and monitoring. The two main ways to secure REST APIs include:

API testing strategies are similar to other software testing methodologies. The main focus is on validating server responses. API testing includes:

• Making multiple requests to API endpoints for performance testing.
• Writing unit tests for checking business logic and functional correctness.
• Security testing by simulating system attacks.
  

Writing comprehensive API documentation is part of the API management process. API documentation can be auto-generated using tools or written manually. Some best practices include:

• Writing explanations in simple, easy-to-read English. Documents generated by tools can become wordy and require editing.
• Using code samples to explain functionality.
• Maintaining the documentation so it is accurate and up-to-date.
• Aiming the writing style at beginners
• Covering all the problems the API can solve for the users.
  

The steps to implement a new API include:

1. Obtaining an API key. This is done by creating a verified account with the API provider.
2. Set up an HTTP API client. This tool allows you to structure API requests easily using the API keys received.
3. If you don’t have an API client, you can try to structure the request yourself in your browser by referring to the API documentation.
4. Once you are comfortable with the new API syntax, you can start using it in your code.
   

New web APIs can be found on API marketplaces and API directories. API marketplaces are open platforms where anyone can list an API for sale. API directories are controlled repositories regulated by the directory owner. Expert API designers may assess and test a new API before adding it to their directory.  

Some popular API websites include:

• Rapid API – The largest global API market with over 10,000 public APIs and 1 million active developers on site. RapidAPI allows users to test APIs directly on the platform before committing to purchase.
• Public APIs – The platform groups remote APIs into 40 niche categories, making it easier to browse and find the right one to meet your needs.
• APIForThat and APIList – Both these websites have lists of 500+ web APIs, along with in-depth information on how to use them.                                                                                                 
  

An API Gateway is an API management tool for enterprise clients that use a broad range of back-end services. API gateways typically handle common tasks like user authentication, statistics, and rate management that are applicable across all API calls.

Amazon API Gateway is a fully managed service that makes it easy for developers to create, publish, maintain, monitor, and secure APIs at any scale. It handles all the tasks involved in accepting and processing thousands of concurrent API calls, including traffic management, CORS support, authorization, and access control, throttling, monitoring, and API version management.

Application Programming Interface management is an important part of modern software development. It is worth investing in API infrastructure, including tools, gateway, and microservices architecture for both internal and external users.

Amazon API Gateway comes with a full range of features to manage multiple APIs simultaneously and efficiently. You can make up to one million API calls for free by signing up at the AWS Portal.

AWS AppSync offers fully managed GraphQL API setup, administration, and maintenance, with high-availability serverless infrastructure built-in. You pay only for what you use with no minimum fees or mandatory service usage. To get started, please sign in to the AWS AppSync Console.