Developer
Someone who builds a tool, a mod or a service on the open SDK, or extends the game itself
The SDK is open under MIT, and its source is the final reference
Start with SDK, then - Installation
Documentation
Command-line arguments that open a screen, a level or a run at once, and switches that change one launch of the game
The open C# library the game reads and writes levels through
How to connect the SDK to a .NET or Unity project and check that it reads your levels
What a level folder holds, which files travel with it and which stay on the device, and how the JSON inside is laid out
The byte layout of a .blob file: the 24-byte header, the order it is checked in and the envelopes inside
How the SDK packs a level into one file or puts it behind a password, and how it recognizes what it was handed
Which number versions what, how an older file is migrated and why a file from a newer build is refused
How the SDK checks a level against the format's rules, repairs what can be repaired and reports what cannot
How a service states which levels it accepts, written as a data file instead of code
How a generator is built from the SDK base classes and what it has to respect to work in the editor
Converting Afterbeat levels, themes and prefabs to the Bullet Hero format and back, and what is lost on the way
Where to report problems, where the SDK's rules for contributors are written down, and how to build, test and pack it