As much as people are willing to pay for it, writes Bob Reselman of SmartBear, a specialist in software quality tools.
"The basic laws of valuation don't go away just because we're living in a world of microservices, PaaS and big data on demand," he writes. "It doesn't matter if you are giving your API away, any more than it applies for trying to get rid of a litter of "free" puppies. If the user is not willing to make the investment of time, attention and support costs, then your API is not worth much."
But there are examples of extremely valuable APIs out there, he notes, and one of the keys is doing for your users what they can't — or would find extremely difficult — to do for themselves.
Check out this handy infographic SmartBear has put together to help you determine the value of your APIs.