What is an API? What does API mean? Explained in Simple English

API (Application Programming Interface) sounds complicated, but it just means “function”!

Photo by Caspar Camille Rubin on Unsplash

An Analogy

  • how does a computer chip work?
  • how do the computer parts talk to each other?
  • how does programming work?

All we care about is how to use a keyboard and a mouse. In other words, keyboard and mouse are the interfaces for us human to use the computer. This applies to other objects as well. For example, in a car, the steering wheel, brake pedal, gear handle are all interfaces for us to drive a car.

Now, in the programming world, there are also needs for interfaces to interact with software. And we call these interfaces API! Hence the name Application Programming Interface, i.e a programming interface for applications 🎮.

Why API?

Why do we need API? Well it is the same reason as why do we need a steering wheel in a car? Though it is technically possible for us to drive a car without a steering wheel (via 💪 and sheer determination) but it is simply impractical. A car is far too complex for an end user.

Similar to a car, the main goal of API is to let the end users be able to easily use a particular program. They only need to know how to use the interface / functions, but not the inner working of the system.

API Deep Dive

  1. Programming API
  2. Web API

Programming API

For example, in JavaScript, we are able to interact with the console via the console API. If we want to log something in the console, we can simply call the log function that is exposed by the console module, or logging an error using the error function, or generic info using the info function:

console.log('heeyy');console.error('something went wrong');console.info('some info');

These functions are collectively known as the Console API in JavaScript.


Modern web applications are often dependent on each other. For example, although Facebook and Instagram are 2 different web app, but we can still share our Instagram post to Facebook within Instagram itself. How does Instagram do that? The magic behinds it is….Web API!

So what composes of a Web Application?

But our transcription service can only work within our app…right?

Well this is exactly where web API solves our problem. Why don’t we expose our transcription service as a function (aka API) so the others can use it externally?

Web API: Behind the scenes

Let’s try to call an API endpoint from Github.

Sample response:

Sample response returned by Github’s public API
Web API: Behind the scenes

So what is happening here?

  1. The server receives the request, and run a function to search for all types of licenses from its database.
  2. Once found, the server sends back a JSON string to the browser and the browser will simply display it. JSON — JavaScript Object Notation is a string format that looks very similar to JavaScript object. It is widely used to transmit data in web API.

In a nutshell, we are simply running a function by sending a HTTP GET request to the Github’s server.

So Web APIs are just functions exposed via URLs by a server.

By using web APIs exposed by another web application, we can leverage features developed by other people so we don’t need to reinvent the wheel.

What about Authentication?

Typical API authentication methods

1. Secret Key / API key / Bearer Token 🔑

An API key is kind of like a password. The server will only process API requests with a valid API Key.

For example, an API request with API key would look something like this:


We are simply passing our API key as a query parameter on our API request!

Although using an API key for authentication is simple, once the key is stolen, it could severely compromise your account.

2. Cookie 🍪

Cookies associated to medium.com

Cookies have a few common uses:

  1. Trackers that identify visitors for marketing purposes.
  2. Security cookies to stop attacks like XSS (cross site scripting).
  3. Authenticating users. Let’s talk more about this.

When you check the ‘remember me’ box when you login to a web app, the app’s server will give you a cookie to store in your browser. From here on, whenever you try to access any resource via web API, your browser will attach this cookie along with your HTTP request. The server will then validate the cookie in the request to make sure the cookie is the one that it sent to the browser before.

3. JWT (JSON Web Token)

When a user logins to an app, the server will issue a JWT to the user. The JWT is then passed along with the subsequent HTTP requests to the server.

JWT is short-lived by convention, typically with a lifetime of 15 min to 1 hour. Whenever it is due to expiry. the browser will request for a new JWT from the server.

JWT has the same security concerns as using an API key. Once it is stolen, the hacker can do pretty much anything to the user’s account. However, due to its short-lived nature, JWT is more secure than using an API key, because the hacker only has a minimal amount of time to wreck havoc.

4. Oauth

That’s it for now!

Additional Resources

Web Development. https://acadea.io/learn . Follow me on Youtube: https://www.youtube.com/c/acadeaio