PATCH

The HTTP PATCH request method applies partial modifications to a resource.

PATCH is somewhat analogous to the "update" concept found in CRUD (in general, HTTP is different than CRUD, and the two should not be confused).

A PATCH request is considered a set of instructions on how to modify a resource. Contrast this with PUT; which is a complete representation of a resource.

A PATCH is not necessarily idempotent, although it can be. Contrast this with PUT; which is always idempotent. The word "idempotent" means that any number of repeated, identical requests will leave the resource in the same state. For example if an auto-incrementing counter field is an integral part of the resource, then a PUT will naturally overwrite it (since it overwrites everything), but not necessarily so for PATCH.

PATCH (like POST) may have side-effects on other resources.

To find out whether a server supports PATCH, a server can advertise its support by adding it to the list in the Allow or Access-Control-Allow-Methods (for CORS) response headers.

Another (implicit) indication that PATCH is allowed, is the presence of the Accept-Patch header, which specifies the patch document formats accepted by the server.

Request has body	Yes
Successful response has body	May
Safe	No
Idempotent	No
Cacheable	No
Allowed in HTML forms	No

PATCH /file.txt HTTP/1.1

PATCH /file.txt HTTP/1.1
Host: www.example.com
Content-Type: application/example
If-Match: "e0023aa4e"
Content-Length: 100

[description of changes]

HTTP/1.1 204 No Content
Content-Location: /file.txt
ETag: "e0023aa4f"