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How do RESTful APIs work? An Insightful Guide

RESTful APIs are the kind of APIs that follow the constraints of a REST architectural style. We have covered a full article on the background architecture of this kind of API, its pros and cons, and its principles. This article focuses mainly on the way the REStful APIs work, client requests, and server responses in these APIs. If you want to get familiar with the way these APIs work and then use different frameworks, follow along with the article to get familiar with the backbone architecture of a RESTful API.

How do RESTful APIs work?

Just the same as browsing the internet, in a RESTful API, The client contacts the server by using the API when it requires a resource. The API developers explain how the client should use the REST API in the server application API documentation. The process that happens in RESTful API, goes like this. First, The client sends a request to the server and writes the request in a format that has been mentioned in the documentation, so that the server can understand. Then, the server confirms if the client has the right to make a request by authenticating him or her. Afterward, the server receives and processes the request internally. And finally, it returns a response containing the request acceptance or rejection and if the request has been accepted, it also returns what the client has requested.

What does the client request look like in a RESTful API?

All the RESTful API requests need to contain the following three main components:
1. URI
2. Method
3. HTTP Headers

What is URI? And how is it used in a client request?

URI is the acronym for Unique Resource Identifier. The server identifies each resource with a URI. In REST services, the server typically performs resource identification by using a URL (an acronym for Uniform Resource Locator). The URL specifies the path to the resource. A URL is similar to the website address that you enter into your browser to visit any webpage. The URL is also called the request endpoint and clearly specifies to the server what the client requires.


RESTful APIs are often implemented using the HTTP (Hypertext Transfer Protocol) methods. These methods do a certain action on the server by telling it what it needs to do to the server. The followings are the four HTTP common methods that is also used in a RESTful API:

1. GET:

Clients use GET to access resources that are located at the specified URL on the server. They can cache GET requests and send parameters in the RESTful API request to instruct the server to filter data before sending. By using the GET request, the client queries the necessary items from a database.

2. POST:

Clients use the POST request to send data to the database. They include the data representation with the request. Sending the same POST request multiple times has the side effect of creating the same resource multiple times.

3. PUT:

Clients use PUT to update existing resources on the server. Unlike POST, sending the same PUT request multiple times in a RESTful web service gives the same result and it does not create new resources.


Clients use the DELETE request to remove the resource. A DELETE request can change the server state. However, if the user does not have appropriate authentication, the request fails.

HTTP headers

Request headers are the metadata exchanged between the client and server. For instance, the request header indicates the format of the request and response, provides information about request status, and so on.


REST API requests might include data for the POST, PUT, and other HTTP methods to work successfully.


RESTful API requests can include parameters that give the server more details about what needs to be done. The following are some different types of parameters:
Path parameters that specify URL details.
Query parameters that request more information about the resource.
Cookie parameters that authenticate clients quickly.

RESTful API authentication methods?

A RESTful web service must authenticate requests before it can send a response. Authentication is the process of verifying identity. For example, you can prove your identity by showing an ID card or driver’s license. Similarly, RESTful service clients must prove their identity to the server to establish trust.
RESTful API has four common authentication methods:

HTTP authentication

HTTP defines some authentication schemes that you can use directly when you are implementing REST API. The following are two of these schemes:

Basic authentication

In basic authentication, the client sends the user name and password in the request header. It encodes them with base64, which is an encoding technique that converts the pair into a set of 64 characters for safe transmission.

Bearer authentication

The term bearer authentication refers to the process of giving access control to the token bearer. The bearer token is typically an encrypted string of characters that the server generates in response to a login request. The client sends the token in the request headers to access resources.

API keys

API keys are another option for REST API authentication. In this approach, the server assigns a unique generated value to a first-time client. Whenever the client tries to access resources, it uses the unique API key to verify itself. API keys are less secure because the client has to transmit the key, which makes it vulnerable to network theft.


OAuth combines passwords and tokens for highly secure login access to any system. The server first requests a password and then asks for an additional token to complete the authorization process. It can check the token at any time and also over time with a specific scope and longevity.

What does the RESTful API server response contain?

REST principles require the server response to contain the following main components:

Status line

The status line contains a three-digit status code that communicates request success or failure. For instance, 2XX codes indicate success, but 4XX and 5XX codes indicate errors. 3XX codes indicate URL redirection.
The following are some common status codes:
200: Generic success response
201: POST method success response
400: Incorrect request that the server cannot process
404: Resource not found
Message body

Message body

The response body contains the resource representation. The server selects an appropriate representation format based on what the request headers contain. Clients can request information in XML or JSON formats, which define how the data is written in plain text. For example, if the client requests the name and age of a person named John, the server returns a JSON representation as follows:
‘{“name”:”Mohamad”, “age”:27}’


The response also contains headers or metadata about the response. They give more context about the response and include information such as the server, encoding, date, and content type.


In this article, you learned about the way the RESTful APIs work, client requests, and server responses in these APIs. By knowing the way the RESTful API works, you can use any kind of framework or language to write a microservice or an API using the REST architecture. Flask, Django, PHP, or any other kind of language or framework or micro-framework can help you create this kind of API. One of the most popular and simple applications created using the RESTful API is CRUD (Create, Read, Update, Delete) application and it can be used for creating a user database or a website or a web application.

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What is a RESTful API? A Complete Guide

REST API and RESTful API are both terms that can be used interchangeably. REST stands for Representational State Transfer and it is a software architectural style that defines a set of certain rules or constraints for creating web services. API is the acronym for Application Programming Interface. REST API is a kind of API that uses the rules defined by the REST architectural style and is also a way of accessing web services in a simple and flexible way without having any processing. Web services that implement REST architecture are called RESTful web services.

What is an API?

An API or an Application Programming Interface is a kind of a gateway between the clients and the resources on the web. These resources contain certain data that can be accessed by rules defined in the API. In other words, API is a way for various applications to communicate with each other. Developers expose or create APIs so that other applications can communicate with their applications programmatically. For instance, suppose you want to create a software that any user can enter their bank account balance and see it in the Bitcoin unit (see how much they will have in Bitcoin if they change all their balance to bitcoin), you will then need an API for retrieving the current price of the BTC at any time. Coin Market Cap API is one of these APIs that can give you the price of BTC at any time. Using this API you can programmatically convert the user’s balance to BTC so that he or she can see it in the BTC unit.

What is a RESTful API?

RESTful API is a kind of application programming interface that two computer systems use to exchange data securely over the internet. Most business applications have to communicate with other internal and third-party applications to perform various tasks. For instance, to generate monthly payslips, your internal accounts system has to share data with your customer’s banking system to automate invoicing and communicate with an internal timesheet application. RESTful APIs support this information exchange because they follow secure, reliable, and efficient software communication standards. These communication standards or the constraints that we previously mentioned need to be applied on the API to be considered as a RESTful API, otherwise this API will lack the standards of a typical RESTful API.

REST Architecture Standards (Constraints)

There are several principles that an API must have in order to be considered a RESTful API. These standards include:

1. Uniform interface
2. Statelessness
3. Layered system
4. Cacheability
5. Code on demand (optional)

All of the above constraints are the standards of the REST architectural style. The 5th one is optional, meaning that if the API lacks it, it will still be considered RESTful. We will take a look at all of these standards one by one to what each of them actually means:

Uniform interface

The uniform interface is fundamental to the design of any RESTful web service. It indicates that the server transfers information in a standard format. The formatted resource is called a representation in REST. This format can be different from the internal representation of the resource on the server application. For example, the server can store data as text but send it in an HTML representation format.

1. Uniform interface imposes four architectural constraints:

2. Requests should identify resources. They do so by using a uniform resource identifier.

3. Clients have enough information in the resource representation to modify or delete the resource if they want to. The server meets this condition by sending metadata that describes the resource further.

4. Clients receive information about how to process the representation further. The server achieves this by sending self-descriptive messages that contain metadata about how the client can best use them.

5. Clients receive information about all other related resources they need to complete a task. The server achieves this by sending hyperlinks in the representation so that clients can dynamically discover more resources.


In REST architecture, statelessness refers to a communication method in which the server completes every client request independently of all previous requests. Clients can request resources in any order, and every request is stateless or isolated from other requests. This REST API design constraint implies that the server can completely understand and fulfill the request every time.

Layered system

In a layered system architecture, the client can connect to other authorized intermediaries between the client and server, and it will still receive responses from the server. Servers can also pass on requests to other servers. You can design your RESTful web service to run on several servers with multiple layers such as security, application, and business logic, working together to fulfill client requests. These layers remain invisible to the client.


RESTful web services support caching, which is the process of storing some responses on the client or on an intermediary to improve server response time. For example, suppose that you visit a website that has common header and footer images on every page. Every time you visit a new website page, the server must resend the same images. To avoid this, the client caches or stores these images after the first response and then uses the images directly from the cache. RESTful web services control caching by using API responses that define themselves as cacheable or noncacheable.

Code on demand (optional)

In REST architectural style, servers can temporarily extend or customize client functionality by transferring software programming code to the client. For example, when you fill a registration form on any website, your browser immediately highlights any mistakes you make, such as incorrect phone numbers. It can do this because of the code sent by the server.

How do RESTful APIs work?

The basic function of a RESTful API is the same as browsing the internet. The client contacts the server by using the API when it requires a resource. API developers explain how the client should use the REST API in the server application API documentation. These are the general steps for any REST API call:

1. The client sends a request to the server. The client follows the API documentation to format the request in a way that the server understands.
2. The server authenticates the client and confirms that the client has the right to make that request.
3. The server receives the request and processes it internally.
4. The server returns a response to the client. The response contains information that tells the client whether the request was successful. The response also includes any information that the client requested.

The REST API request and response details vary slightly depending on how the API developers design the API.


In this article, you learned about the APIs, REST architectural style and its principles, and finally the RESTful API. Of course, there is a lot to discuss about these APIs such as the requests and the responses in a RESTful API and the authentication methods. We will talk about these topics in the next articles. Moreover, there are frameworks like Django and Flask using which you can create RESTful APIs like the CRUD API (Create, Read, Update, Delete). We have covered the codes and the implementations of these APIs in Python on the blog tutorials section where you can head over and visit our tutorial contents.

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