HTTP Methods, Status Codes and their meaning

Have you ever wondered what's the difference between GET and POST requests, or what does 404 Not Found means? You're not alone. Having a basic understanding of the different HTTP Methods and HTTP Status Codes is important when you're exploring and testing APIs.

HTTP Methods:

Below are some common HTTP methods. Let's discuss what each of them means.

GET:

GET method is used to retrieve data from a server at the specified resource.
GET is often the default method in HTTP clients

POST:

POST requests are used to send data to the API server to create or update a resource. The data sent to the server is stored in the request body of the HTTP request.
The simplest example is a contact form on a website. When you fill out the inputs in a form and hit Send, that data is put in the response body of the request and sent to the server.

PUT:

Similar to POST, PUT requests are used to send data to the API to update or create a resource. The difference is that PUT requests are idempotent. That is, calling the same PUT request multiple times will always produce the same result. In contrast, calling a POST request repeatedly make have side effects of creating the same resource multiple times.

PATCH:

PATCH is used for modifying capabilities. The PATCH request only needs to contain the changes to the resource, not the complete resource.
This resembles PUT, but the body contains a set of instructions describing how a resource currently residing on the server should be modified to produce a new version. This means that the PATCH body should not just be a modified part of the resource, but in some kind of patch languages like JSON Patch or XML Patch.

DELETE:

DELETE is pretty easy to understand. It is used to delete a resource identified by a URI.

HTTP Response Status Codes:

HTTP response status codes indicate whether a specific HTTP request has been successfully completed. Responses are grouped into five classes. Let's touch upon some most common HTTP response status codes from all these classes in this blog.

• Informational responses (100–199)

• Successful responses (200–299)
  200 OK: The request was completed successfully.

• Redirects (300–399)
  301 Moved Permanently: The resource is permanently located in a different URI. A new URI should be given in the response.
  302 Found: The resource temporarily moved to a new location.

• Client errors (400–499)
  400 Bad Request: The request could not be understood by the server.
  401 Unauthorized: The request has not been applied because it lacks valid authentication credentials for the target resource.
  403 Forbidden: User not authorized to perform the requested operation.
  404 Not Found: The requested resource could not be found at the given URI.
  405 Method Not Allowed: The request method is not allowed on the specified resource.

• Server errors (500–599)
  500 Internal Server Error: The server encountered an unexpected condition, preventing it to fulfill the request.
  503 Service Unavailable: The server is temporarily unavailable, usually due to overloading or maintenance.
  504 Gateway Timeout: The server is a gateway or proxy server, and it is not receiving a response from the backend servers within the allowed time period.

Further References:

Here are some resources where you can refer to more of these HTTP Methods and HTTP Response Status Codes.
MDN - HTTP Methods
MDN - HTTP Response Status Codes