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Mis à jour le 30/03/2022

Use Postman to Make Your Requests

Identify the Pros of Postman

You already know that a REST API involves sending requests from the client to the API, which passes the request on to the server. The API then retrieves the response and returns it to the client. In this chapter, we will look at how to make these requests using Postman.

Lots of developers use this graphical interface. It makes it easier to create requests, making it the ideal tool for testing APIs without having to use any code.

It’s also the tool that we’ll be using in this course!

Cool, but why Postman?

Because there are lots of pros to this particular interface:

  • You can use it no matter what language you’re programming in.

  • It has a sleek user interface; you can make requests easily.

  • You don’t need to know how to code  

Download Postman

It’s time to take the plunge and download Postman

Select your operating system. Postman is available for use with Linux, Windows, and OS X.

Postman's home page: on the left side of the interface the icons propose to download your operating system.
The Postman home page

Once you’ve done that, you’ll be redirected to a page for downloading the software. Click on the button Download the App.

The Postman download button for MacBook
The download button for Postman on MacBook

Perfect! And now we can move onto making requests. 😃

Make a Request on Postman

The Structure of Requests

Every request has a specific structure:

HTTP Verb + URI + HTTP Version + Headers + Optional Message Body

A typical request structure in 3 overlapping layers: at the bottom the body, in the middle the headers, above the HTTP verb, the URI and the HTTP version.
A typical request structure

It can look different depending on the software or language you use.

A Request in Postman

Now that you’ve launched the program, let’s take a look at what a request looks like in Postman.

You should see this:

The field used to perform a query in Postman is indicated in green in the Workspaces tab of the interface.
Field used to make a request in Postman

Oh dear, that looks a bit complicated!

Don’t panic! We’ll break down each zone one by one, following the structure of a request:

Example of HTTP verb with GET: displayed on the left.
Example of an HTTP verb with GET

Let’s start with verbs. HTTP verbs are different types of actions you can take with your request – the most common ones you’ll see are GET, PUT, POST, and DELETE. We'll cover these all in more depth later.

To the right of GET is the url https://api.github.com/users/facebook
The full request URL includes the domain name: api.github.com and the URI or resource path: /users/facebook

Moving on now to the URI. A URI is how you identify resources. For example, if you want to see all the users on your website, the path would be:


Now let’s say you wanted to get information for a specific user. You’ll need to specify their ID, so it would be something like:


Why have we suddenly switched from using a number to :user_id ? 🤔

You use :user_id to represent the user ID – it’s a placeholder. In practice, with a real ID, the path would look more like this: users/145.

The Content-Type and Authorization headers are displayed in a query.
Headers in a request

header enables you to pass along additional information about the message. For example:

  • What language is it?

  • What date are you sending it on?

  • What software is the person using?

  • What is your authentication key?

Headers are in a key-value pair, and there are many different types of options for them. For example:

Date: Tue, 19 Jan 2019 18:15:41 GMT

User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5)

You can check out this full list of header options.  

The body is displayed from the Body tab of the request.
A message body
Message Body

And finally, the message body. When making a request, this is only used with PUT or POST HTTP verbs. It contains the actual data of the resource you are trying to create or update. The data is sent using JSON.

Quick reminder: JSON is widely used, but certain APIs might only accept XML. You’ll find this information in the documentation of the API you’re using.

Let’s look at an example. You want to add or update a user’s information, so you add the user details (name, last name, address, etc.) in the body (in JSON).

See how the message body is optional in both cases? This means that it is totally possible to send an empty message body depending on the API actions you want.

You’ll learn more about this in the coming chapters. 🕵🏻‍♀️

Get a Response With Postman

Request structure done ✅ ! Let’s move on to responses.

response message has a similar format to the request:

HTTP Version + HTTP Response Code + Headers + Message Body

A typical response structure in 3 overlapping layers: at the bottom the Body, in the middle the Header and above the HTTP version and code.
A typical response structure

In Postman, you can see a response message that looks like this:

A typical Postman response message is displayed on the interface in the Body tab.
A typical response message

Wait a second. The message body? But isn’t that only used to make a request with POST and PUT? 🤔

To make a request, yes! But for responses, the message body has the information you asked for and the API has returned. This is signaled within the message body in JSON or XML. The image above shows a successful response for a request to the GitHub API. 

And if it is unsuccessful? What happens then? Do we get different information? 🤔

Exactly! If the request was unsuccessful, the message body could have an error message:

An unsuccessful request
An unsuccessful request

However, the message isn’t enough, and sometimes APIs don't send any messages at all, whether the request is successful or not. This is rare, though! In such cases, your best friend is the HTTP response code

Analyze the HTTP Response Code

The HTTP response code helps the developer or client understand the status of the response. Here are the requests in Postman:

Screenshot of a message reading Status: 200 OK
A successful HTTP status code
Screenshot of a message reading Status: 404 Not Found
An unsuccessful HTTP status code

When a client sends a request like, “Hey, can you send me all the tweets for this user?” You can think of the response code as something like a traffic light 🚥  telling you:

GREEN ✅ : “This request was successfully processed.” 


RED 🔴 : “We could not find anything about this request!”

There are a lot of different response codes - one you are probably familiar with is 404 Not Found. You may have seen this on a few websites. For example, when you try to go to a page that doesn't exist, you'll see something like:

GitHub 404 response page
GitHub 404 response page

Another important response code to know is 200 OK - which means your request was successful, and your response is good to go! In general, the rule of thumb for HTTP response codes is:

  • 100+ ➡ Informational

  • 200+ ➡ Success

  • 300+ ➡ Redirection

  • 400+ ➡ Client error

  • 500+ ➡ Server error

HTTP codes are very standard, and each number corresponds to a specific response. So, all APIs will return a 404 if the resource is not found, and this means developers will understand what type of response they’re getting. It’s a sort of generalized naming system that everyone sticks to.

If you have any doubts about an HTTP code, take a look at this documentation, which contains more detailed information. 

Let’s Recap!

  • Postman is a free software for making API requests without any code. 

  • Requests take the form:
    HTTP Verb + URI + HTTP Version + Headers + Optional Message Body.

  • HTTP verbs are possible types of actions to take when making a request.

  • Responses take the form:
    HTTP Response Code + HTTP Version + Headers + Message Body.

  • HTTP response codes are a kind of traffic light 🚦 with specific codes to let clients know whether a given request was processed successfully or not. 

  • HTTP codes are standardized according to the type of response; you’ll find a list here.

Next chapter, we’ll be rolling up our sleeves and starting to work with real APIs! So that your learning can be as effective as possible, it’s important to know the general format of requests and responses and what successful and unsuccessful responses look like!

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