What is an Application Programming Interface(API)? How does it work: Definition, Function, Example, Types

July 6, 2021

What is an Application Programming Interface(API)? How does it work: Definition, Function, Example, Types


An API is defined as a specification of possible interactions with a software component. API is the acronym for Application Programming Interface, which is a software intermediary that allows two applications to interact with each other. Each time you use an app like Whatsapp or check the calendar on your mobile phone, you’re using an API.

It is a computing interface that defines interactions between multiple software or mixed hardware-software intermediaries. It defines the kinds of calls or requests that can be made, how to make them, the data formats that should be used, the conventions to follow, etc. It can also provide extension mechanisms so that users can extend existing functionality in various ways and to varying degrees. An API can be entirely custom, specific to a component, or designed based on an industry-standard to ensure interoperability. Through information hiding, APIs enable modular programming, allowing users to use the interface independently of the implementation.

What Is an Example of an API?

When using mobile applications, your application is connecting to the Internet which then transports data to a specific server. Upon retrieval, the server interprets this data in order to execute the required actions before sending the information back to your device. This is how your applications present you with information that you can read and understand. This process is API.

Imagine that you’re sitting in a coffee shop with an extensive menu before you. The kitchen will process your order as per their “system.” However, how are you going to communicate to them what it is that you want? The link that you’re missing is that of “communication.” This is where the server would come in– the API. API is the hostess, who listens to your request and informs the system as to how they ought to proceed. The hostess would then deliver the food back to you from the kitchen, as an API would respond.

An API example in our day-to-day life can look like using websites to interact with live databases, such as when booking a flight. You can choose from a vast array of departure or return dates, cities, cabin classes, and even seats. Then based on your inquiries, the API will let you know what is available.

On the contrary, it is also possible that you won’t be using a channel with direct access to this information. Let’s say that you opt for an online travel booking instead. Sites such as Skyscanner and Kayak aggregate data from a variety of airline databases to aid their clients.

In this case, the travel service is working with the airline’s API specifically. In this circumstance, the API is the interface being asked by the online travel service, for information regarding the airline’s seat availability, baggage options, etc. The API will then give the airline’s response to the online travel service as per your inquiry, which will then grant you updated information.


Here’s how an API works:

  • The client’s application will initiate an API call to seek information. This is known as a request. The API’s URI (Uniform Resource Identifier) will then process the request from the application to a web server. This URI can include a request body, as well as a request verb and headers.
  • Upon receiving a valid request, the API will call upon the external program or web server.
  • This server is what will send a response to the API along with the information being requested.
  • The API is what will transfer the data to the application that sent out the initial request.

Naturally, this transfer of data will differ depending on which web service is being used, but the entire process of requests and responses will happen entirely through an API. While user interfaces are designed for human use, APIs are designed to be used by applications or computers.

By virtue of their design, APIs offer security. This is because APIs are positioned as middlemen. Their position is what facilitates the abstraction of functionality between multiple systems. It is the API endpoint that provides the service by decoupling the consuming application from the infrastructure. In order to minimize the risk of attacks on a given server, API calls typically include authorization credentials. API gateways are also known to limit access in order to reduce the chance of security threats. To provide additional layers of security to data during an exchange, HTTP headers, cookies, and query string parameters can be implemented.

Consider payment processing services that utilize an API. Within a given e-commerce store, customers have the option to enter their card details on the frontend of the application. Rather than the payment processor itself requiring access to the user’s bank account, API will create a unique token for the transaction. This token will then be included within the API call to the server. This process is what ensures the aforementioned increased levels of security against potential hacking threats.