When do you use POST and when do you use GET?

Question

From what I can gather, there are three categories:

1. Never use GET and use POST
2. Never use POST and use GET
3. It doesn't matter which one you use.

Am I correct in assuming those three cases? If so, what are some examples from each case?

Answer 1

Well one major thing is anything you submit over GET is going to be exposed via the URL. Secondly as Ceejayoz says, there is a limit on characters for a URL.

Answer 2

HTTP Post data doesn't have a specified limit on the amount of data, where as different browsers have different limits for GET's. The RFC 2068 states:

Servers should be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations may not properly support these lengths

Specifically you should the right HTTP constructs for what they're used for. HTTP GET's shouldn't have side-effects and can be safely refreshed and stored by HTTP Proxies, etc.

HTTP POST's are used when you want to submit data against a url resource.

A typical example for using HTTP GET is on a Search, i.e. Search?Query=my+query A typical example for using a HTTP POST is submitting feedback to an online form.

Answer 3

Because GETs are purely URLs, they can be cached by the web browser and may be better used for things like consistently generated images. (Set an Expiry time)

One example from the gravatar page: http://www.gravatar.com/avatar/4c3be63a4c2f539b013787725dfce802?d=monsterid

GET may yeild marginally better performance, some webservers write POST contents to a temporary file before invoking the handler.

Another thing to consider is the size limit. GETs are capped by the size of the URL, 1024 bytes by the standard, though browsers may support more.

Transferring more data than that should use a POST to get better browser compatibility.

Even less than that limit is a problem, as another poster wrote, anything in the URL could end up in other parts of the brower's UI, like history.