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Understanding RESTful API: An In-depth Overview

 · 5 min · Pallavi Varandani

The article provides a comprehensive overview of RESTful API, covering HTTP methods, their classification, idempotent and non-idempotent operations, and HTTP status codes. It emphasizes the importance of understanding these concepts for building effective and scalable web applications.

Restful APIs Introduction


RESTful API (Representational State Transfer) is a widely used architectural style for designing networked applications. It provides a standardized approach for communication between clients and servers over the internet. In this article, we will delve into the key concepts of RESTful API and explore its various components, including HTTP methods, request/response pairs, and status codes.

Classification of HTTP Methods

The classification of HTTP methods can be further categorized as follows:

  • Read Method: Read methods in the context of HTTP methods refer to operations that retrieve or fetch information from a server without modifying or altering any data. The primary HTTP method associated with read operations is the GET method.

  • Write Methods: Write methods, on the other hand, are used for operations that modify or manipulate data on the server. These methods enable the creation, modification, or deletion of resources. The common write methods used in RESTful APIs are PUT, POST, and DELETE.

  • Idempotent Methods: Idempotent methods are operations that can be applied multiple times without causing any additional or different effects beyond the initial application. In other words, repeating an idempotent method should produce the same result as the first application. The idempotent HTTP methods include GET, DELETE, and PUT.

  • Non-idempotent Method: Non-idempotent methods, in contrast, may have varying outcomes when applied multiple times. Each application of a non-idempotent method may result in a different state or effect. The non-idempotent HTTP method commonly used in RESTful APIs is POST.

ClassificationHTTP Methods
Read MethodGET
Write MethodsPUT, POST, DELETE
Idempotent MethodsGET, DELETE, PUT
Non-idempotent MethodPOST

HTTP Methods in Practice

RESTful APIs rely on the use of HTTP methods to perform specific actions on resources. Here are the commonly used HTTP methods:

Other Noteworthy HTTP Methods

Apart from the commonly used HTTP methods, there are a few additional methods that serve specific purposes within the RESTful API architecture:

  • HEAD: Similar to GET, the HEAD method retrieves server headers for a specific resource without including the message body. It is often used to check if the resource has changed by comparing timestamps.

  • TRACE: The TRACE method allows the client to retrieve the hops taken by a request to round trip from the server. It can be utilized for diagnostic purposes by inspecting the Via header field.

  • OPTIONS: By employing the OPTIONS method, the client can retrieve information about the server’s capabilities. It helps in modifying the request based on the server’s supported features.

HTTP Status Codes and Their Meanings

When a client makes a request to a server, the server responds with an HTTP status code to indicate the result of the request. Here are some commonly encountered HTTP status codes:

2xx: Successful

  • 200 OK: Indicates that the request was successfully processed. For a GET request, the server includes the requested resource in the response’s message body.
  • 202 Accepted: Signifies that the request was accepted, but the response may not include the resource. It is often used for asynchronous processing on the server, where the server may provide additional information for monitoring.
  • 204 No Content: Denotes that there is no message body in the response.
  • 205 Reset Content: Instructs the client to reset its document view.
  • 206 Partial Content: Indicates that the response contains only partial content. Additional headers provide information about the exact range and content expiration.

3xx: Redirection

  • 301 Moved Permanently: Specifies that the requested resource is now located at a new URL.
  • 303 See Other: Temporarily points to a different URL where the requested resource can be found. The Location response header contains the temporary URL.
  • 304 Not Modified: Informs the client that the resource has not changed, and it should use its cached copy. This relies on the client sending an ETag (Entity Tag), which is a hash of the content. The server compares the client’s ETag with its own to check for modifications.

4xx: Client Error

  • 400 Bad Request: Indicates that the request was malformed.
  • 401 Unauthorized: Requires authentication. The client can repeat the request with the Authorization header, and if the header was already included, it means the credentials were incorrect.
  • 403 Forbidden: Denies access to the resource.
  • 405 Method Not Allowed: Occurs when an invalid HTTP verb is used in the request line or when the server does not support the provided verb.
  • 409 Conflict: Arises when the server cannot complete the request because the client is attempting to modify a resource that is newer than the client’s timestamp. Conflicts often occur during collaborative edits on a resource, primarily with PUT requests.

5xx: Server Error

  • 500 Internal Server Error: Indicates a server failure while processing the request.
  • 501 Not Implemented: Specifies that the server does not yet support the requested functionality.
  • 503 Service Unavailable: Occurs when an internal system on the server has failed or when the server is overloaded, causing the server to be unavailable.


Understanding RESTful API is essential for building modern web applications that communicate effectively with servers. By grasping the key concepts discussed in this article, including HTTP methods, request/response pairs, and status codes, developers can design and implement robust and efficient APIs. Remember, a well-designed RESTful API adheres to the principles of simplicity, scalability, and ease of use, providing a solid foundation for building successful applications.