what points i should consider to create API for a new website i am building? [closed]

Question

What points i should consider while building a website, and planing to support users with API to use?

I see that most of famous websites are giving developers an API to deal with, such as facebook, twitter, google, ....

There are any general points i should consider while building a new website to be able to support developers with an API? "just very general points regardless the website service its self"

UPDATE all answers below helped me a lot.

Answer 1

Soap or XML

Depending on your application. If it is complex you might need the functionality of soap. KISS should apply with APIs especially. Have a sensible URL layout that makes sense in terms of resources:

www.site.com/people/london

As a resource.

http://en.wikipedia.org/wiki/Restful

Look into why using PUT, POST, GET and others is important.

Good Luck