Is there any limit or fee to use facebook api? Can I develop a commercial software with faceboo api?
Questions on Web Applications Stack Exchange are expected to relate to web applications within the scope defined in the FAQ. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about closed questions here.
This is best answered already on StackOverflow:
You can develop commercial software with the API, read the dev policy for more details. If you exceed the limits above you'll probably have to pay.