qmk_firmware/docs/adding_features_to_qmk.md

How To Add Features To QMK

If you have an idea for a custom feature or extra hardware connection, we'd love to accept it into QMK!

Before you put a lot of work into building your new feature you should make sure you are implementing it in the best way. You can get a basic understanding of QMK by reading Understaning QMK, which will take you on a tour of the QMK program flow. From here you should talk to us to get a sense of the best way to implement your idea. There are two main ways to do this:

• Chat on Gitter
• Open an Issue

Once you have implemented your new feature you will generally submit a pull request. Here are some things to keep in mind when creating one:

• Disabled by default - memory is a pretty limited on most chips QMK supports, and it's important that current keymaps aren't broken, so please allow your feature to be turned on, rather than being turned off. If you think it should be on by default, or reduces the size of the code, please talk with us about it.
• Compile locally before submitting - hopefully this one is obvious, but things need to compile! Our Travis system will catch any issues, but it's generally faster for you to compile a few keyboards locally instead of waiting for the results to come back.
• Consider subprojects and different chip-bases - there are several keyboards that have subprojects that allow for slightly different configurations, and even different chip-bases. Try to make a feature supported in ARM and AVR, or automatically disabled on platforms it doesn't work on.
• Explain your feature - Document it in docs/, either as a new file or as part of an existing file. If you don't document it other people won't be able to benefit from your hard work.
• Don't refactor code - to maintain a clear vision of how things are laid out in QMK, we try to plan out refactors in-depth, and have a collaborator make the changes. If you have an idea for refactoring, or suggestions, open an issue, we'd love to talk about how QMK can be improved.