Mod-Tap

The Mod-Tap key MT(mod, kc) acts like a modifier when held, and a regular keycode when tapped. In other words, you can have a key that sends Escape when you tap it, but functions as a Control or Shift key when you hold it down.

The modifiers this keycode and OSM() accept are prefixed with MOD_, not KC_:

Modifier

Description

MOD_LCTL

Left Control

MOD_LSFT

Left Shift

MOD_LALT

Left Alt

MOD_LGUI

Left GUI (Windows/Command/Meta key)

MOD_RCTL

Right Control

MOD_RSFT

Right Shift

MOD_RALT

Right Alt (AltGr)

MOD_RGUI

Right GUI (Windows/Command/Meta key)

MOD_HYPR

Hyper (Left Control, Shift, Alt and GUI)

MOD_MEH

Meh (Left Control, Shift, and Alt)

You can combine these by ORing them together like so:

MT(MOD_LCTL | MOD_LSFT, KC_ESC)

This key would activate Left Control and Left Shift when held, and send Escape when tapped.

For convenience, QMK includes some Mod-Tap shortcuts to make common combinations more compact in your keymap:

Key

Aliases

Description

LCTL_T(kc)

CTL_T(kc)

Left Control when held, kc when tapped

LSFT_T(kc)

SFT_T(kc)

Left Shift when held, kc when tapped

LALT_T(kc)

LOPT_T(kc), ALT_T(kc), OPT_T(kc)

Left Alt when held, kc when tapped

LGUI_T(kc)

LCMD_T(kc), LWIN_T(kc), GUI_T(kc), CMD_T(kc), WIN_T(kc)

Left GUI when held, kc when tapped

RCTL_T(kc)

Right Control when held, kc when tapped

RSFT_T(kc)

Right Shift when held, kc when tapped

RALT_T(kc)

ROPT_T(kc), ALGR_T(kc)

Right Alt when held, kc when tapped

RGUI_T(kc)

RCMD_T(kc), RWIN_T(kc)

Right GUI when held, kc when tapped

SGUI_T(kc)

SCMD_T(kc), SWIN_T(kc)

Left Shift and GUI when held, kc when tapped

LCA_T(kc)

Left Control and Alt when held, kc when tapped

LSA_T(kc)

Left Shift and Alt when held, kc when tapped

RSA_T(kc)

SAGR_T(kc)

Right Shift and Right Alt (AltGr) when held, kc when tapped

RCS_T(kc)

Right Control and Right Shift when held, kc when tapped

LCAG_T(kc)

Left Control, Alt and GUI when held, kc when tapped

RCAG_T(kc)

Right Control, Alt and GUI when held, kc when tapped

C_S_T(kc)

Left Control and Shift when held, kc when tapped

MEH_T(kc)

Left Control, Shift and Alt when held, kc when tapped

HYPR_T(kc)

ALL_T(kc)

Left Control, Shift, Alt and GUI when held, kc when tapped - more info here

Caveats

Currently, the kc argument of MT() is limited to the Basic Keycode set, meaning you can't use keycodes like LCTL(), KC_TILD, or anything greater than 0xFF. This is because QMK uses 16-bit keycodes, of which 3 bits are used for the function identifier, 1 bit for selecting right or left mods, and 4 bits to tell which mods are used, leaving only 8 bits for the keycode. Additionally, if at least one right-handed modifier is specified in a Mod-Tap, it will cause all modifiers specified to become right-handed, so it is not possible to mix and match the two - for example, Left Control and Right Shift would become Right Control and Right Shift.

Expanding this would be complicated, at best. Moving to a 32-bit keycode would solve a lot of this, but would double the amount of space that the keymap matrix uses. And it could potentially cause issues, too. If you need to apply modifiers to your tapped keycode, Tap Dance can be used to accomplish this.

You may also run into issues when using Remote Desktop Connection on Windows. Because these keycodes send key events faster than a human, Remote Desktop could miss them. To fix this, open Remote Desktop Connection, click on "Show Options", open the the "Local Resources" tab, and in the keyboard section, change the drop down to "On this Computer". This will fix the issue, and allow the characters to work correctly. It can also be mitigated by increasing TAP_CODE_DELAY.

Other Resources

See the Tap-Hold Configuration Options for additional flags that tweak Mod-Tap behavior.