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Configuring QMK

QMK is nearly infinitely configurable. Wherever possible we err on the side of allowing users to customize their keyboard, even at the expense of code size. That level of flexibility makes for a daunting configuration experience, however.

There are three main types of configuration files in QMK:

  • config.h, which contains various preprocessor directives (#define, #ifdef)
  •, which contains additional variables
  • info.json, which is utilized for data-driven configuration

This page will only discuss the first two types, config.h and


While not all settings have data-driven equivalents yet, keyboard makers are encouraged to utilize the info.json file to set the metadata for their boards when possible. See the info.json Format page for more details.

These files exist at various levels in QMK and all files of the same type are combined to build the final configuration. The levels, from lowest priority to highest priority, are:

  • QMK Default
  • Keyboard
  • Folders (Up to 5 levels deep)
  • Keymap

QMK Default

Every available setting in QMK has a default. If that setting is not set at the Keyboard, Folder, or Keymap level this is the setting that will be used.


This level contains config options that should apply to the whole keyboard. Some settings won't change in revisions, or most keymaps. Other settings are merely defaults for this keyboard and can be overridden by folders and/or keymaps.


Some keyboards have folders and sub-folders to allow for different hardware configurations. Most keyboards only go 1 folder deep, but QMK supports structures up to 5 folders deep. Each folder can have its own config.h and files that are incorporated into the final configuration.


This level contains all of the options for that particular keymap. If you wish to override a previous declaration, you can use #undef <variable> to undefine it, where you can then redefine it without an error.

The config.h File

This is a C header file that is one of the first things included, and will persist over the whole project (if included). Lots of variables can be set here and accessed elsewhere. The config.h file shouldn't be including other config.h files.

Hardware Options

  • #define VENDOR_ID 0x1234
    • defines your VID, and for most DIY projects, can be whatever you want
  • #define PRODUCT_ID 0x5678
    • defines your PID, and for most DIY projects, can be whatever you want
  • #define DEVICE_VER 0x0100
    • defines the device version (often used for revisions)
  • #define MANUFACTURER "Me"
    • generally who/whatever brand produced the board
  • #define PRODUCT "Board"
    • the name of the keyboard
  • #define MATRIX_ROWS 5
    • the number of rows in your keyboard's matrix
  • #define MATRIX_COLS 15
    • the number of columns in your keyboard's matrix
  • #define MATRIX_ROW_PINS { D0, D5, B5, B6 }
    • pins of the rows, from top to bottom
    • may be omitted by the keyboard designer if matrix reads are handled in an alternate manner. See low-level matrix overrides for more information.
  • #define MATRIX_COL_PINS { F1, F0, B0, C7, F4, F5, F6, F7, D4, D6, B4, D7 }
    • pins of the columns, from left to right
    • may be omitted by the keyboard designer if matrix reads are handled in an alternate manner. See low-level matrix overrides for more information.
  • #define MATRIX_IO_DELAY 30
    • the delay in microseconds when between changing matrix pin state and reading values
  • #define MATRIX_HAS_GHOST
    • define is matrix has ghost (unlikely)
    • On un-select of matrix pins, rather than setting pins to input-high, sets them to output-high.
    • COL2ROW or ROW2COL - how your matrix is configured. COL2ROW means the black mark on your diode is facing to the rows, and between the switch and the rows.
  • #define DIRECT_PINS { { F1, F0, B0, C7 }, { F4, F5, F6, F7 } }
    • pins mapped to rows and columns, from left to right. Defines a matrix where each switch is connected to a separate pin and ground.
  • #define AUDIO_VOICES
    • turns on the alternate audio voices (to cycle through)
  • #define C4_AUDIO
    • enables audio on pin C4
    • Deprecated. Use #define AUDIO_PIN C4
  • #define C5_AUDIO
    • enables audio on pin C5
    • Deprecated. Use #define AUDIO_PIN C5
  • #define C6_AUDIO
    • enables audio on pin C6
    • Deprecated. Use #define AUDIO_PIN C6
  • #define B5_AUDIO
    • enables audio on pin B5 (duophony is enabled if one of B pins is enabled along with one of C pins)
    • Deprecated. Use #define AUDIO_PIN B5, or use #define AUDIO_PIN_ALT B5 if a C pin is enabled with AUDIO_PIN
  • #define B6_AUDIO
    • enables audio on pin B6 (duophony is enabled if one of B pins is enabled along with one of C pins)
    • Deprecated. Use #define AUDIO_PIN B6, or use #define AUDIO_PIN_ALT B6 if a C pin is enabled with AUDIO_PIN
  • #define B7_AUDIO
    • enables audio on pin B7 (duophony is enabled if one of B pins is enabled along with one of C pins)
    • Deprecated. Use #define AUDIO_PIN B7, or use #define AUDIO_PIN_ALT B7 if a C pin is enabled with AUDIO_PIN
  • #define BACKLIGHT_PIN B7
    • pin of the backlight
  • #define BACKLIGHT_LEVELS 3
    • number of levels your backlight will have (maximum 31 excluding off)
    • enables backlight breathing
  • #define BREATHING_PERIOD 6
    • the length of one backlight "breath" in seconds
  • #define DEBOUNCE 5
    • the delay when reading the value of the pin (5 is default)
    • mechanical locking support. Use KC_LCAP, KC_LNUM or KC_LSCR instead in keymap
    • tries to keep switch state consistent with keyboard LED state
  • #define IS_COMMAND() (get_mods() == MOD_MASK_SHIFT)
    • key combination that allows the use of magic commands (useful for debugging)
    • sets the maximum power (in mA) over USB for the device (default: 500)
    • sets the USB polling rate in milliseconds for the keyboard, mouse, and shared (NKRO/media keys) interfaces
    • sets the number of milliseconds to pause after sending a wakeup packet. Disabled by default, you might want to set this to 200 (or higher) if the keyboard does not wake up properly after suspending.
  • #define F_SCL 100000L
    • sets the I2C clock rate speed for keyboards using I2C. The default is 400000L, except for keyboards using split_common, where the default is 100000L.

Features That Can Be Disabled

If you define these options you will disable the associated feature, which can save on code size.

  • #define NO_DEBUG
    • disable debugging
  • #define NO_PRINT
    • disable printing/debugging using hid_listen
  • #define NO_ACTION_LAYER
    • disable layers
    • disable tap dance and other tapping features
    • disable one-shot modifiers

Features That Can Be Enabled

If you define these options you will enable the associated feature, which may increase your code size.

    • Enables the QK_MAKE keycode
  • #define FORCE_NKRO
    • NKRO by default requires to be turned on, this forces it on during keyboard startup regardless of EEPROM setting. NKRO can still be turned off but will be turned on again if the keyboard reboots.
    • force a key release to be evaluated using the current layer stack instead of remembering which layer it came from (used for advanced cases)

Behaviors That Can Be Configured

  • #define TAPPING_TERM 200
    • how long before a key press becomes a hold
    • enables handling for per key TAPPING_TERM settings
  • #define RETRO_TAPPING
    • tap anyway, even after TAPPING_TERM, if there was no other key interruption between press and release
    • See Retro Tapping for details
    • enables handling for per key RETRO_TAPPING settings
  • #define TAPPING_TOGGLE 2
    • how many taps before triggering the toggle
    • makes tap and hold keys trigger the hold if another key is pressed before releasing, even if it hasn't hit the TAPPING_TERM
    • See Permissive Hold for details
    • enabled handling for per key PERMISSIVE_HOLD settings
  • #define QUICK_TAP_TERM 100
    • tap-then-hold timing to use a dual role key to repeat keycode
    • See Quick Tap Term
    • Changes the timing of Tap Toggle functionality (TT or the One Shot Tap Toggle)
    • Defaults to TAPPING_TERM if not defined
    • enables handling for per key QUICK_TAP_TERM settings
    • selects the hold action of a dual-role key as soon as the tap of the dual-role key is interrupted by the press of another key.
    • See "hold on other key press" for details
    • enables handling for per key HOLD_ON_OTHER_KEY_PRESS settings
  • #define LEADER_TIMEOUT 300
    • how long before the leader key times out
      • If you're having issues finishing the sequence before it times out, you may need to increase the timeout setting. Or you may want to enable the LEADER_PER_KEY_TIMING option, which resets the timeout after each key is tapped.
    • sets the timer for leader key chords to run on each key press rather than overall
    • Disables keycode filtering for Mod-Tap and Layer-Tap keycodes. Eg, if you enable this, you would need to specify MT(MOD_CTL, KC_A) if you want to use KC_A.
    • Enables support for extended reports (-32767 to 32767, instead of -127 to 127), which may allow for smoother reporting, and prevent maxing out of the reports. Applies to both Pointing Device and Mousekeys.
  • #define ONESHOT_TIMEOUT 300
    • how long before oneshot times out
  • #define ONESHOT_TAP_TOGGLE 2
    • how many taps before oneshot toggle is triggered
  • #define COMBO_TERM 200
    • how long for the Combo keys to be detected. Defaults to TAPPING_TERM if not defined.
    • Flag for enabling extending timeout on Combos containing modifiers
  • #define COMBO_MOD_TERM 200
    • Allows for extending COMBO_TERM for mod keys while mid-combo.
    • Flag to enable per-combo COMBO_TERM extension and get_combo_must_hold() function
    • Flag to enable per-combo COMBO_TERM extension and get_combo_term() function
    • Only start the combo timer on the first key press instead of on all key presses.
  • #define COMBO_NO_TIMER
    • Disable the combo timer completely for relaxed combos.
  • #define TAP_CODE_DELAY 100
    • Sets the delay between register_code and unregister_code, if you're having issues with it registering properly (common on VUSB boards). The value is in milliseconds and defaults to 0.
  • #define TAP_HOLD_CAPS_DELAY 80
    • Sets the delay for Tap Hold keys (LT, MT) when using KC_CAPS_LOCK keycode, as this has some special handling on MacOS. The value is in milliseconds, and defaults to 80 ms if not defined. For macOS, you may want to set this to 200 or higher.
    • Enables magic configuration handling for advanced keycodes (such as Mod Tap and Layer Tap)

RGB Light Configuration

  • #define WS2812_DI_PIN D7
    • pin the DI on the WS2812 is hooked-up to
    • Lets you define lighting layers that can be toggled on or off. Great for showing the current keyboard layer or caps lock state.
    • Defaults to 8. Can be expanded up to 32 if more lighting layers are needed.
    • Note: Increasing the maximum will increase the firmware size and slow sync on split keyboards.
    • Adds ability to blink a lighting layer for a specified number of milliseconds (e.g. to acknowledge an action).
  • #define RGBLIGHT_LED_COUNT 12
    • number of LEDs
  • #define RGBLIGHT_SPLIT
    • Needed if both halves of the board have RGB LEDs wired directly to the RGB output pin on the controllers instead of passing the output of the left half to the input of the right half
  • #define RGBLED_SPLIT { 6, 6 }
    • number of LEDs connected that are directly wired to the RGB pin on each half of a split keyboard
    • First value indicates number of LEDs for left half, second value is for the right half
    • When RGBLED_SPLIT is defined, RGBLIGHT_SPLIT is implicitly defined.
  • #define RGBLIGHT_HUE_STEP 12
    • units to step when in/decreasing hue
  • #define RGBLIGHT_SAT_STEP 25
    • units to step when in/decreasing saturation
  • #define RGBLIGHT_VAL_STEP 12
    • units to step when in/decreasing value (brightness)
  • #define WS2812_RGBW
    • Enables RGBW LED support

Mouse Key Options

  • #define MOUSEKEY_INTERVAL 20
  • #define MOUSEKEY_DELAY 0
  • #define MOUSEKEY_TIME_TO_MAX 60
  • #define MOUSEKEY_MAX_SPEED 7

Split Keyboard Options

Split Keyboard specific options, make sure you have 'SPLIT_KEYBOARD = yes' in your

  • SPLIT_TRANSPORT = custom
    • Allows replacing the standard split communication routines with a custom one. ARM based split keyboards must use this at present.

Setting Handedness

One thing to remember, the side that the USB port is plugged into is always the master half. The side not plugged into USB is the slave.

There are a few different ways to set handedness for split keyboards (listed in order of precedence):

  1. Set SPLIT_HAND_PIN: Reads a pin to determine handedness. If pin is high, it's the left side, if low, the half is determined to be the right side
  2. Set EE_HANDS and flash eeprom-lefthand.eep/eeprom-righthand.eep to each half
    • For boards with DFU bootloader you can use :dfu-split-left/:dfu-split-right to flash these EEPROM files
    • For boards with Caterina bootloader (like stock Pro Micros), use :avrdude-split-left/:avrdude-split-right
    • For boards with ARM DFU bootloader (like Proton C), use :dfu-util-split-left/:dfu-util-split-right
  3. Set MASTER_RIGHT: Half that is plugged into the USB port is determined to be the master and right half (inverse of the default)
  4. Default: The side that is plugged into the USB port is the master half and is assumed to be the left half. The slave side is the right half

Defines for handedness

  • #define SPLIT_HAND_PIN B7

    • For using high/low pin to determine handedness, low = right hand, high = left hand. Replace B7 with the pin you are using. This is optional, and if you leave SPLIT_HAND_PIN undefined, then you can still use the EE_HANDS method or MASTER_LEFT / MASTER_RIGHT defines like the stock Let's Split uses.
  • #define SPLIT_HAND_MATRIX_GRID <out_pin>,<in_pin>

    • The handedness is determined by using the intersection of the keyswitches in the key matrix, which does not exist. Normally, when this intersection is shorted (level low), it is considered right. If you define #define SPLIT_HAND_MATRIX_GRID_LOW_IS_LEFT, it is determined to be left when the level is low.
  • #define EE_HANDS (only works if SPLIT_HAND_PIN and SPLIT_HAND_MATRIX_GRID are not defined)

    • Reads the handedness value stored in the EEPROM after eeprom-lefthand.eep/eeprom-righthand.eep has been flashed to their respective halves.
  • #define MASTER_RIGHT

    • Master half is defined to be the right half.

Other Options

  • #define USE_I2C

    • For using I2C instead of Serial (default is serial; serial transport is supported on ARM -- I2C is AVR-only)
  • #define SOFT_SERIAL_PIN D0

    • When using serial, define this. D0 or D1,D2,D3,E6.
  • #define MATRIX_ROW_PINS_RIGHT { <row pins> }

  • #define MATRIX_COL_PINS_RIGHT { <col pins> }

    • If you want to specify a different pinout for the right half than the left half, you can define MATRIX_ROW_PINS_RIGHT/MATRIX_COL_PINS_RIGHT. Currently, the size of MATRIX_ROW_PINS must be the same as MATRIX_ROW_PINS_RIGHT and likewise for the definition of columns.
    • may be omitted by the keyboard designer if matrix reads are handled in an alternate manner. See low-level matrix overrides for more information.
  • #define DIRECT_PINS_RIGHT { { F1, F0, B0, C7 }, { F4, F5, F6, F7 } }

    • If you want to specify a different direct pinout for the right half than the left half, you can define DIRECT_PINS_RIGHT. Currently, the size of DIRECT_PINS must be the same as DIRECT_PINS_RIGHT.
  • #define RGBLED_SPLIT { 6, 6 }

  • #define SELECT_SOFT_SERIAL_SPEED <speed> (default speed is 1)

    • Sets the protocol speed when using serial communication
    • Speeds:
      • 0: about 189kbps (Experimental only)
      • 1: about 137kbps (default)
      • 2: about 75kbps
      • 3: about 39kbps
      • 4: about 26kbps
      • 5: about 20kbps
  • #define SPLIT_USB_DETECT

    • Detect (with timeout) USB connection when delegating master/slave
    • Default behavior for ARM
    • Required for AVR Teensy (without hardware mods)
  • #define SPLIT_USB_TIMEOUT 2000

    • Maximum timeout when detecting master/slave when using SPLIT_USB_DETECT

    • Poll frequency when detecting master/slave when using SPLIT_USB_DETECT

    • Reboot slave if no communication from master within timeout.
    • Helps resolve issue where both sides detect as slave using SPLIT_USB_DETECT

    • Maximum slave timeout when waiting for communication from master when using SPLIT_WATCHDOG_ENABLE

    • Deadline for synchronizing data from master to slave when using the QMK-provided split transport.

    • Mirrors the master-side matrix on the slave when using the QMK-provided split transport.

    • Ensures the current layer state is available on the slave when using the QMK-provided split transport.

    • Ensures the current host indicator state (caps/num/scroll) is available on the slave when using the QMK-provided split transport.

    • Ensures the current modifier state (normal, weak, and oneshot) is available on the slave when using the QMK-provided split transport.
  • #define SPLIT_WPM_ENABLE

    • Ensures the current WPM is available on the slave when using the QMK-provided split transport.

    • Syncs the on/off state of the OLED between the halves.
  • #define SPLIT_ST7565_ENABLE

    • Syncs the on/off state of the ST7565 screen between the halves.
  • #define SPLIT_TRANSACTION_IDS_KB .....


The File

This is a make file that is included by the top-level Makefile. It is used to set some information about the MCU that we will be compiling for as well as enabling and disabling certain features.

Build Options

    • Used to specify a default folder when a keyboard has more than one sub-folder.
    • Defines which format (bin, hex) is copied to the root qmk_firmware folder after building.
  • SRC
    • Used to add files to the compilation/linking list.
    • Used to add files as a library to the compilation/linking list. The files specified by LIB_SRC is linked after the files specified by SRC. For example, if you specify:
      SRC += a.c
      LIB_SRC += lib_b.c
      SRC += c.c
      LIB_SRC += lib_d.c
      The link order is as follows.
       ...  a.o c.o  ...  lib_b.a lib_d.a  ...
    • A list of layouts this keyboard supports.
    • Enables Link Time Optimization (LTO) when compiling the keyboard. This makes the process take longer, but it can significantly reduce the compiled size (and since the firmware is small, the added time is not noticeable).

AVR MCU Options

  • MCU = atmega32u4
  • F_CPU = 16000000
  • ARCH = AVR8
  • F_USB = $(F_CPU)
  • BOOTLOADER = atmel-dfu with the following options:
    • atmel-dfu
    • lufa-dfu
    • qmk-dfu
    • halfkay
    • caterina
    • bootloadhid
    • usbasploader

Feature Options

Use these to enable or disable building certain features. The more you have enabled the bigger your firmware will be, and you run the risk of building a firmware too large for your MCU.

    • MAGIC actions (BOOTMAGIC without the boot)
    • Enable Bootmagic Lite
    • Mouse keys
    • Audio control and System control
    • Console for debug
    • Commands for debug and configuration
    • Key combo feature
    • USB 6-Key Rollover - Instead of stopping any new input once 6 keys are pressed, the oldest key is released and the new key is pressed.
    • Enable the audio subsystem.
    • Enable the key override feature
    • Enable keyboard underlight functionality
    • Enable leader key chording
    • MIDI controls
    • Unicode
    • Current options are bluefruit_le, rn42
    • Enables split keyboard support (dual MCU like the let's split and bakingpy's boards) and includes all necessary files located at quantum/split_common
    • Allows replacing the standard matrix scanning routine with a custom one.
    • Allows replacing the standard key debouncing routine with an alternative or custom one.
    • Forces the keyboard to wait for a USB connection to be established before it starts up
    • Disables usb suspend check after keyboard startup. Usually the keyboard waits for the host to wake it up before any tasks are performed. This is useful for split keyboards as one half will not get a wakeup call but must send commands to the master.
    • Enables deferred executor support -- timed delays before callbacks are invoked. See deferred execution for more information.
    • Allows to configure the global tapping term on the fly.

USB Endpoint Limitations

In order to provide services over USB, QMK has to use USB endpoints. These are a finite resource: each microcontroller has only a certain number. This limits what features can be enabled together. If the available endpoints are exceeded, a build error is thrown.

The following features can require separate endpoints:


In order to improve utilisation of the endpoints, the HID features can be combined to use a single endpoint. By default, MOUSEKEY, EXTRAKEY, and NKRO are combined into a single endpoint.

The base keyboard functionality can also be combined into the endpoint, by setting KEYBOARD_SHARED_EP = yes. This frees up one more endpoint, but it can prevent the keyboard working in some BIOSes, as they do not implement Boot Keyboard protocol switching.

Combining the mouse also breaks Boot Mouse compatibility. The mouse can be uncombined by setting MOUSE_SHARED_EP = no if this functionality is required.