It is inconceivable that Twitter would be as popular as it is today without its robust Application Programming Interface, which allows client applications like TweetDeck and the original Tweetie (since bought by Twitter and re-branded as its official client app) to both display a user’s stream of tweets and manipulate his or her account in all the ways he or she would on Twitter.com itself.

So depending on your perspective, it’s either surprising that Google+ did not launch with a developer API, or it’s surprising that they have come out with one relatively quickly, given the amount of testing and tweaking an entirely new social network no doubt involves.

Either way, Google+ finally has an API, although it’s read-only, and it only shows the Google+ posts that a user has made public. In the coming days and weeks, we’re going to see a handful of uses of this API, which, in the abstract, at this point is little more than an RSS or XML feed for a user’s public posts.

Once Google allows its API to write as well as read, Twitter-style clients will arrive on the service. Or perhaps client applications already suited to Twitter will add Google+ functionality, allowing G+ to piggyback on their popularity.

Whatever happens, it’s hard to imagine Google+ remaining the stimulating hive of conversation that it is—at least for some of us—without the addition of a robust ecosystem of apps built by outside developers. Serious users of Twitter know this is true: nothing beats a client app in terms of speed and flexibility, and empowering the 1 percent of users who generate the majority of your content is how a service moves from being a toy to something like a public utility, as Twitter has become.