Behaviors Overview

"Behaviors" are bindings that are assigned to and triggered by key positions on keymap layers, sensors (like an encoder) or combos. They describe what happens e.g. when a certain key position is pressed or released, or an encoder triggers a rotation event. They can also be recursively invoked by other behaviors, such as macros.

Below is a summary of pre-defined behavior bindings and user-definable behaviors available in ZMK, with references to documentation pages describing them.

Key press behaviors

Binding	Behavior	Description
&kp	Key Press	Send keycodes to the connected host when a key is pressed
&mt	Mod Tap	Sends a different key press depending on whether a key is held or tapped
&kt	Key Toggle	Toggles the press of a key. If the key is not currently pressed, key toggle will press it, holding it until the key toggle is pressed again or the key is released in some other way. If the key is currently pressed, key toggle will release it
&sk	Sticky Key	Stays pressed until another key is pressed, then is released. It is often used for modifier keys like shift, which allows typing capital letters without holding it down
&gresc	Grave Escape	Sends Grave Accent ` keycode if shift or GUI is held, sends Escape keycode otherwise
&caps_word	Caps Word	Behaves similar to caps lock, but automatically deactivates when any key not in a continue list is pressed, or if the caps word key is pressed again
&key_repeat	Key Repeat	Sends again whatever keycode was last sent

Miscellaneous behaviors

Binding	Behavior	Description
&trans	Transparent	Passes the key press down to the next active layer in the stack for processing
&none	None	Swallows and stops the key press, no keycode will be sent nor will the key press be passed down to the next active layer in the stack

Layer navigation behaviors

Binding	Behavior	Description
&mo	Momentary Layer	Enables a layer while a key is pressed
&lt	Layer-tap	Enables a layer when a key is held, and outputs a key press when the key is only tapped for a short time
&to	To Layer	Enables a layer and disables all other layers except the default layer
&tog	Toggle Layer	Enables a layer until the layer is manually disabled
&sl	Sticky Layer	Activates a layer until another key is pressed, then deactivates it

Mouse emulation behaviors

Binding	Behavior	Description
&mkp	Mouse Button Press	Emulates pressing mouse buttons

Reset behaviors

Binding	Behavior	Description
&sys_reset	Reset	Resets the keyboard and re-runs the firmware flashed to the device
&bootloader	Bootloader	Resets the keyboard and puts it into bootloader mode, allowing you to flash new firmware

Output selection behaviors

Binding	Behavior	Description
&bt	Bluetooth	Completes a bluetooth action given on press, for example switching between devices
&out	Output Selection	Allows selecting whether output is sent to the USB or bluetooth connection when both are connected

Lighting behaviors

Binding	Behavior	Description
&rgb_ug	RGB Underglow	Controls the RGB underglow, usually placed underneath the keyboard
&bl	Backlight	Controls the keyboard backlighting, usually placed through or under switches

Power management behaviors

Binding	Behavior	Description
&ext_power	Power management	Allows enabling or disabling the VCC power output to save power
&soft_off	Soft off	Turns the keyboard off.

User-defined behaviors

Behavior	Description
Macros	Allows configuring a list of other behaviors to invoke when the key is pressed and/or released
Hold-Tap	Invokes different behaviors depending on key press duration or interrupting keys. This is the basis for layer-tap and mod-tap
Tap Dance	Invokes different behaviors corresponding to how many times a key is pressed
Mod-Morph	Invokes different behaviors depending on whether a specified modifier is held during a key press
Sensor Rotation	Invokes different behaviors depending on whether a sensor is rotated clockwise or counter-clockwise