What does PATCH do in REST semantics?

• A. Replaces a resource completely
• B. Creates a resource
• C. Deletes a resource
• D. Partially updates a resource

Answer: (D)

PATCH is used to apply partial updates to a resource. Instead of sending the entire resource to replace it, you send only the changes you want to make, and the server applies those changes to the existing resource, leaving unspecified fields untouched. This makes PATCH ideal for small, targeted updates—for example, changing just a user’s email or a single property in a product record.

This differs from replacing completely, which is what PUT does: PUT sends a full resource representation and replaces the existing one. Creating a resource is typically done with POST (or PUT in some idempotent creation scenarios), not PATCH. Deleting a resource is done with DELETE.

Common patches come in formats like JSON Patch (a sequence of operations) or JSON Merge Patch (a diff-like structure), both aimed at describing the specific changes to apply rather than the whole resource.