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When should we use PUT and when should we use POST?

The HTTP methods POST and PUT aren't the HTTP equivalent of the CRUD's create and update. They both serve a different purpose. It's quite possible, valid and even preferred in some occasions, to use POST to create resources, or use PUT to update resources.

Use PUT when you can update a resource completely through a specific resource. For instance, if you know that an article resides at http://example.org/article/1234, you can PUT a new resource representation of this article directly through a PUT on this URL.

If you do not know the actual resource location, for instance, when you add a new article, but do not have any idea where to store it, you can POST it to an URL, and let the server decide the actual URL.

PUT /article/1234 HTTP/1.1
    
    
         
     
      12.50
     
    

POST /articles HTTP/1.1
    
    
         
     
      7.50
     
    
HTTP/1.1 201 CreatedLocation: /articles/63636

As soon as you know the new resource location, you can use PUT again to do updates to the blue stapler article. But as said before: you CAN add new resources through PUT as well. The next example is perfectly valid if your API provides this functionality:

PUT /articles/green-stapler HTTP/1.1
    
    
         
     
      9.95
     
    
HTTP/1.1 201 CreatedLocation: /articles/green-stapler

Here, the client decided on the actual resource URL.

Caveats

• PUT and POST are both unsafe methods. However, PUT is idempotent, while POST is not.

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