API - post updates

Can someone give me a working example of an API call for adding tags to a post (and maybe another one for changing the source)? I've been trying some variations but just can't get it to work; I just get redirected to the post in question with no changes.

Make sure you're submitting it as a POST request, not a GET request. Here's an example in Javascript.

POST, hm. Up until this point I was just using /post/index.json and /artist/index.json, so I guess I was just used to GET.

I was writing in Java, but thanks for the tip. I'll work on it more later.