qmk_firmware/keyboards/handwired/symmetric70_proto/promicro/info.json

{
    "keyboard_name": "Symmetric70 prototype promicro",
    "features": {
        "bootmagic": true,
        "mousekey": false,
        "extrakey": false
    },
    "split": {
        "soft_serial_pin": "D0"
    },
    "processor": "atmega32u4",
    "bootloader": "caterina"
}