This lets developers fetch only public data from user profiles in a read-only manner, and application calls are limited to what Google calls a "courtesy usage quota" for now.

Google sees this initial API release as the first step in building a more powerful and sophisticated developer platform. "For all of you developers who have been asking for a Google+ API, this is the start. Experiment with it. Build apps on it. Give us your feedback and ideas," Chris Chabot, from the Google+ Developer Relations team, in a blog post.

Creating a thriving developer community, as Twitter and Facebook have done, has proven a must for social networking sites to succeed, so a lot is riding on the Google+ application development platform. Twitter announced in July that some 750,000 developers have built about 1 million applications for its microblogging service.

Interestingly, Google is holding off on adopting for Google+ the OpenSocial APIs that it originally developed in 2007 and championed for years as a better alternative to proprietary tools for specific platforms like Facebook's.

Google conceived OpenSocial as a standard, common set of APIs for social networking sites to adopt, so that developers could build applications once and have them work on multiple sites with little or no modifications.