Ask HN: How common is it to charge customers for API access?

[joshdance]

http://www.yardi.com/anz/services/interfaces/ - Yardi is a property management solution I think. We had one of their customers want to connect to our system. Yardi charges $25,000 a year PER API of which there are 9.

That seems insane to me. How common is it to charge your customers that are already paying you more to use an API?

[savethefuture]

If you offer it as a new service or option than it makes perfect sense to charge them again.