USV just announced the investment in Twitter. I told a friendly VC about it before we announced today and he replied, “That’s the worst kept secret on the Internet today.” Ok, so maybe our blogs forecasted this one, and there’s no surprise here… but, I’ve never been one for secrecy. Comes with the territory of being a self-proclaimed openness junkie.

Getting back to Twitter, I’ve spent a few months now stalking the Twitter Dev Group and the Twitter Fan Wiki. The community that has developed around this investment is really something special. I think there’s a couple reasons for this great dev community group hug.

• Brad’s right: “It’s the API, stupid.”
• But, it’s also the simplicity. There are almost 500 APIs listed on programmable web, and Twitter’s 3rd party development activity is in the upper-eschelon of all APIs. So, it’s more than just the API… it’s because it’s a great API that was built in parallel to the site. A programmer could recreate nearly all of Twitter.com using the API, yet the API can be understood completely in a couple hours. The API-exposed functionality is both deep and simple.
• Great site design. The pages are beautiful and clean by default, but they are also totally customizable so that you can make your homepage your own. If you take pride in how your product looks, others will share the pride. And, allowing people to customize their look and feel gives them a sense of ownership in the site. It’s a great one-two punch, and I think it’s a big part of the reason why developers got so inspired in creating Twitter API implementations.
• Community: The API feels like much more than a doc. It’s a living, breathing community of people that are ready and waiting to help each other, and, more importantly, show off for each other.
• First Party Support. When you make a cool API implementation, Twitter supports your work. Check out their download page: it’s all third-party apps listed directly on the first-party site. There’s not many other web services that support and embrace the work of their third-party developers so strongly.

I love the dev culture around Twitter, and I’m looking forward to to seeing what third-party developers think of next.