What is the difference between PUT and POST methods in the HTTP protocol?

PUT is used to update an existing resource or create a new one at the specified URI if it does not exist. It is idempotent – repeated calls with the same request body to the same URI should have the same effect as the first.

POST is used to send data to the server for processing. It is not idempotent and may cause different effects upon repeated calls. It is typically used to create a new resource, submit form data, or invoke an action on the server.

Key differences:

Attribute	PUT	POST
Purpose	Replace/create resource at URI	Send data for processing/creation
Idempotency	Yes	No (usually)
URI	Points to the target resource	Points to the resource where data is sent
Side effects	Same for repeated requests	Can vary for repeated requests