What is the function of the PATCH HTTP method?

The PATCH HTTP method is designed specifically for making partial updates to a resource. When a client sends a PATCH request, it includes only the changes to be applied rather than sending the entire resource representation. This allows for more efficient and streamlined updates, particularly in situations where the resource is large or complex.

For example, if a user wants to update just the email address field in a user profile resource, they can send a PATCH request with only that specific field, rather than having to resend the entire profile. This method is particularly useful in RESTful APIs, where bandwidth and performance are concerns, and it enables clients to change a resource's state more efficiently without modifying the whole entity.

The distinction between PATCH and other methods is crucial. While methods like POST are used for creation of resources and PUT typically requires the full representation of the resource to replace the existing one, PATCH focuses solely on the modifications needed, making it an integral part of RESTful web services.