Just days ahead of the Project Ara Developers Conference, Google has released the first version of the Module Developers Kit (MDK).

The 81-page MDK goes into detail about the three sizes of endo skeletons and how the ribs and spines must be laid out. A Medium endo is made up of a 3x6 grid of modules with a spine that’s at a 1:2 offset from the center of the unit. Meanwhile, Mini and Large endos consist of 2x5 and 4x7 module grids and have centered spines.

The MDK also goes into detail about the design of Ara phones and the modules that’ll be attached to them. Google says that the modules should “create a smooth, flat, pebble form” so that they’re easy to insert into the slots and that the completed devices are “enjoyable to handle.” The company also gives guidelines for how the modules should be shaped. Interestingly, Google says that camera modules can extend out from an Ara device’s body.

Google previously revealed that it hopes to have the first commercially-available Ara phones ready by the first quarter of 2015. Between now and then, it will educate developers and manufacturers on how to create the modules that’ll make up those units. This early version of the MDK gives us a nice preview of what we can expect from Google’s modular smartphone effort, and with the the Project Ara Developers Conference scheduled for next week, it won’t be long before we learn even more.

Via Project Ara