PUT and POST are two of the most common HTTP methods that are used to send data to a server. They both have similarities and differences, and understanding them is essential for designing and consuming RESTful APIs.

The PUT method is used to create or replace a resource at a specific URI. The URI identifies the resource that will be modified or created by the request. The request body contains the representation of the resource that will be stored under the URI. The PUT method is idempotent, which means that sending the same request multiple times will have the same effect as sending it once. The PUT method is not cacheable, which means that the response cannot be stored by intermediate proxies or caches¹.

An example of a PUT request is:

This request will create or replace the user resource at /users/123 with the JSON data in the body.

The POST method is used to submit data to a resource for processing. The URI identifies the resource that will handle the data, but not necessarily the resource that will be created or modified by the request. The request body can contain any data that is relevant for the processing. The POST method is not idempotent, which means that sending the same request multiple times may have different effects, such as creating multiple resources or triggering multiple actions. The POST method can be cacheable, but only if the server sets the appropriate headers to indicate that the response can be stored¹.