Everyday there is more written and presented about what makes a good API.

In recent years, much discussion related to APIs has focused on architectural approach (e.g., SOAP-based web services vs. RESTful ones) or even how a specific approach (like REST) is best applied. Beyond all the blog-blather about APIs (this post included among the blather), there also is an increasing number of market metrics as to the type of APIs, as well as the particular APIs, that are gaining the most adoption.

Some of the metrics come from the API publishers themselves. For example, a key data point frequently cited with regard to Amazon web services (offered in both SOAP and RESTful configurations) is that 20 percent of the usage is SOAP, while 80 percent is REST. There also are a few independent sources of information about API usage. SOA analyst and born-again cloud-computing evangelist David Lithicum highlighted in one of his recent podcasts the website Programmableweb.com, which provides a directory of, and community feedback on, more than 1,000 APIs.

What Makes a Good API?

I won't try to recreate the aforementioned blog blather about what makes a good API, but if you want to be spoon-fed a good, high-level introduction on this topic there really are few better sources than the webcast embedded below (also available here) by Joshua Bloch, a senior software engineer and architect at Google. This is a high-level review of technical design principles. I have a follow-up regarding one of Bloch's early statements in the webcast about API's as "business assets," which I'll get to below the embed.