Glass Development Kit
The Glass Development Kit (GDK) is an add-on to the Android SDK that lets you build Glassware that runs directly on Glass.
Design and develop for Glass with the GDK
The GDK is an Android SDK add-on that contains APIs for Glass-specific features.
By using the Android SDK and GDK, you can leverage the vast array of Android APIs and also design a great experience for Glass.
Unlike the Mirror API, Glassware built with the GDK runs on Glass itself, allowing access to low-level hardware features.
Work in the Android environment
We designed the Glass platform to make the existing Android SDK just work on Glass. This lets you code in a familiar environment, but for a uniquely novel device.
In addition, you can use all of the existing Android development tools, and your Glassware is even delivered as a standard Android package (APK).
You'll need a solid background in Android before moving on, so go to the Android developer site if you need to brush up on your skills.
When you're ready, check out these resources to start developing Glassware.