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Hold-Tap Behavior

Summary​

Hold-tap is the basis for other behaviors such as layer-tap and mod-tap.

Simply put, the hold-tap key will output the 'hold' behavior if it's held for a while, and output the 'tap' behavior when it's tapped quickly.

Hold-Tap​

The graph below shows how the hold-tap decides between a 'tap' and a 'hold'.

Simple behavior

By default, the hold-tap is configured to also select the 'hold' functionality if another key is tapped while it's active:

Hold preferred behavior

We call this the 'hold-preferred' flavor of hold-taps. While this flavor may work very well for a ctrl/escape key, it's not very well suited for home-row mods or layer-taps. That's why there are two more flavors to choose from: 'tap-preferred' and 'balanced'.

Flavors​

  • The 'hold-preferred' flavor triggers the hold behavior when the tapping-term-ms has expired or another key is pressed.
  • The 'balanced' flavor will trigger the hold behavior when the tapping-term-ms has expired or another key is pressed and released.
  • The 'tap-preferred' flavor triggers the hold behavior when the tapping-term-ms has expired. Pressing another key within tapping-term-ms does not affect the decision.
  • The 'tap-unless-interrupted' flavor triggers a hold behavior only when another key is pressed before tapping-term-ms has expired. It triggers the tap behavior in all other situations.

When the hold-tap key is released and the hold behavior has not been triggered, the tap behavior will trigger.

Hold-tap comparison

Basic Usage​

For basic usage, please see the mod-tap and layer-tap pages.

Advanced Configuration​

tapping-term-ms​

Defines how long a key must be pressed to trigger Hold behavior.

quick-tap-ms​

If you press a tapped hold-tap again within quick-tap-ms milliseconds of the first press, it will always trigger the tap behavior. This is useful for things like a backspace, where a quick tap+hold holds backspace pressed. Set this to a negative value to disable. The default is -1 (disabled).

require-prior-idle-ms​

require-prior-idle-ms is like quick-tap-ms however it will apply for any non-modifier key pressed before it. This effectively disables the hold-tap when typing quickly, which can be quite useful for homerow mods. It can also have the effect of removing the input delay when typing quickly.

For example, the following hold-tap configuration enables require-prior-idle-ms with a 125 millisecond term, alongside quick-tap-ms with a 200 millisecond term.

rpi: require_prior_idle {
    compatible = "zmk,behavior-hold-tap";
    #binding-cells = <2>;
    flavor = "tap-preferred";
    tapping-term-ms = <200>;
    quick-tap-ms = <200>;
    require-prior-idle-ms = <125>;
    bindings = <&kp>, <&kp>;
};

If you press &kp A and then &rpi LEFT_SHIFT B within 125 ms, then ab will be output. Importantly, b will be output immediately since it was within the require-prior-idle-ms, without waiting for a timeout or an interrupting key. In other words, the &rpi LEFT_SHIFT B binding will only have its underlying hold-tap behavior if it is pressed 125 ms after the previous key press; otherwise it will act like &kp B.

Note that the greater the value of require-prior-idle-ms is, the harder it will be to invoke the hold behavior, making this feature less applicable for use-cases like capitalizing letters while typing normally. However, if the hold behavior isn't used during fast typing, then it can be an effective way to mitigate misfires.

retro-tap​

If retro-tap is enabled, the tap behavior is triggered when releasing the hold-tap key if no other key was pressed in the meantime. The hold key does not activate until another key is pressed, meaning that it cannot be used for mouse events like Shift Click to select from your cursor position to mouse position.

For example, if you press &mt LEFT_SHIFT A and then release it without pressing another key, it will output a.

&mt {
    retro-tap;
};

hold-while-undecided​

If enabled, the hold behavior will immediately be held on hold-tap press, and will release before the behavior is sent in the event the hold-tap resolves into a tap. With most modifiers this will not affect typing, and is useful for using modifiers with the mouse.

Alt/Win/Cmd behavior

In some applications/desktop environments, pressing Alt keycodes by itself will have its own behavior like activate a menu and Gui keycodes will bring up the start menu or an application launcher.

hold-while-undecided-linger​

If your tap behavior activates the same modifier as the hold behavior, and you want to avoid a double tap when transitioning from the hold to the tap, you can use hold-while-undecided-linger. When enabled, the hold behavior will continue to be held until after the tap behavior is released. For example, if the hold is &kp LGUI and the tap is &sk LGUI, then with hold-while-undecided-linger enabled, the host will see LGUI held down continuously until the sticky key is finished, instead of seeing a release and press when transitioning from hold to sticky key.

Positional hold-tap and hold-trigger-key-positions​

Including hold-trigger-key-positions in your hold-tap definition turns on the positional hold-tap feature. With positional hold-tap enabled, if you press any key NOT listed in hold-trigger-key-positions before tapping-term-ms expires, it will produce a tap.

In all other situations, positional hold-tap will not modify the behavior of your hold-tap. Positional hold-tap is useful when used with home-row modifiers: for example, if you have a home-row modifier key in the left hand, by including only key positions from the right hand in hold-trigger-key-positions, you will only get hold behaviors during cross-hand key combinations.

info

Note that hold-trigger-key-positions is an array of key position indexes. Key positions are numbered sequentially according to your keymap, starting with 0. So if the first key in your keymap is Q, this key is in position 0. The next key (probably W) will be in position 1, et cetera.

See the following example, which uses a hold-tap behavior definition, configured with the hold-preferred flavor, and with positional hold-tap enabled:

#include <dt-bindings/zmk/keys.h>
#include <behaviors.dtsi>

/ {
    behaviors {
        pht: positional_hold_tap {
            compatible = "zmk,behavior-hold-tap";
            #binding-cells = <2>;
            flavor = "hold-preferred";
            tapping-term-ms = <400>;
            quick-tap-ms = <200>;
            bindings = <&kp>, <&kp>;
            hold-trigger-key-positions = <1>;    // <---[[the W key]]
        };
    };
    keymap {
        compatible = "zmk,keymap";
        default_layer {
            bindings = <
                //  position 0         position 1       position 2
                &pht LEFT_SHIFT Q        &kp W            &kp E
            >;
        };
    };
};
  • The sequence (pht_down, E_down, E_up, pht_up) produces qe. The normal hold behavior (LEFT_SHIFT) IS modified into a tap behavior (Q) by positional hold-tap because the first key pressed after the hold-tap key is the E key, which is in position 2, which is NOT included in hold-trigger-key-positions.
  • The sequence (pht_down, W_down, W_up, pht_up) produces W. The normal hold behavior (LEFT_SHIFT) is NOT modified into a tap behavior (Q) by positional hold-tap because the first key pressed after the hold-tap key is the W key, which is in position 1, which IS included in hold-trigger-key-positions.
  • If the LEFT_SHIFT / Q key is held by itself for longer than tapping-term-ms, a hold behavior is produced. This is because positional hold-tap only modifies the behavior of a hold-tap if another key is pressed before the tapping-term-ms period expires.

By default, hold-trigger-key-positions are evaluated upon the first key press after the hold-tap. For homerow mods, this is not always ideal, because it prevents combining multiple modifiers unless they are included in hold-trigger-key-positions. To overwrite this behavior, one can set hold-trigger-on-release. If set to true, the evaluation of hold-trigger-key-positions gets delayed until key release. This allows combining multiple modifiers when the next key is held, while still deciding the hold-tap in favor of a tap when the next key is tapped.

Using different behavior types with hold-taps​

You can create instances of hold-taps invoking most behavior types for hold or tap actions, by referencing their node labels in the bindings value. The two parameters that are passed to the hold-tap in your keymap will be forwarded to the referred behaviors, first one to the hold behavior and second one to the tap.

If you use behaviors that accept no parameters such as mod-morphs or macros, you can pass a dummy parameter value such as 0 to the hold-tap when you use it in your keymap. For instance, a hold-tap with node label caps and bindings = <&kp>, <&caps_word>; can be used in the keymap as below to send the caps lock keycode on hold and invoke the caps word behavior on tap:

&caps CAPS 0
info

You cannot use behaviors that expect more than one parameter such as &bt and &rgb_ug with hold-taps, due to the limitations of the devicetree keymap format. One workaround is to create a macro that invokes those behaviors and use the macro as the hold or tap action.

Example Use-Cases​

The following are suggested hold-tap configurations that work well with home row mods:

Option 1: cross-hand only modifiers, using tap-unless-interrupted and positional hold-tap (hold-trigger-key-positions)​
Homerow Mods: Cross-hand Example
#include <dt-bindings/zmk/keys.h>
#include <behaviors.dtsi>

/ {
    behaviors {
        lh_pht: left_positional_hold_tap {
            compatible = "zmk,behavior-hold-tap";
            #binding-cells = <2>;
            flavor = "tap-unless-interrupted";
            tapping-term-ms = <100>;                        // <---[[produces tap if held longer than tapping-term-ms]]
            quick-tap-ms = <200>;
            bindings = <&kp>, <&kp>;
            hold-trigger-key-positions = <5 6 7 8 9 10>;    // <---[[right-hand keys]]
        };
    };

    keymap {
        compatible = "zmk,keymap";
        default_layer {
            bindings = <
                // position 0     pos 1             pos 2             pos 3             pos 4    pos 5    pos 6    pos 7    pos 8    pos 9    pos 10
                &lh_pht LSFT A    &lh_pht LGUI S    &lh_pht LALT D    &lh_pht LCTL F    &kp G    &kp H    &kp I    &kp J    &kp K    &kp L    &kp SEMI
            >;
        };
    };
};
Option 2: tap-preferred​
Homerow Mods: Tap-Preferred Example
#include <behaviors.dtsi>
#include <dt-bindings/zmk/keys.h>

/ {
    behaviors {
        hm: homerow_mods {
            compatible = "zmk,behavior-hold-tap";
            #binding-cells = <2>;
            tapping-term-ms = <150>;
            quick-tap-ms = <0>;
            flavor = "tap-preferred";
            bindings = <&kp>, <&kp>;
        };
    };

    keymap {
        compatible = "zmk,keymap";
        default_layer {
            bindings = <
                &hm LCTRL A &hm LGUI S &hm LALT D &hm LSHIFT F
            >;
        };
    };
};
Option 3: balanced​
Homerow Mods: Balanced Example
#include <behaviors.dtsi>
#include <dt-bindings/zmk/keys.h>

/ {
    behaviors {
        bhm: balanced_homerow_mods {
            compatible = "zmk,behavior-hold-tap";
            #binding-cells = <2>;
            tapping-term-ms = <200>;    // <---[[moderate duration]]
            quick-tap-ms = <0>;
            flavor = "balanced";
            bindings = <&kp>, <&kp>;
        };
    };

    keymap {
        compatible = "zmk,keymap";
        default_layer {
            bindings = <
                &bhm LCTRL A &bhm LGUI S &bhm LALT D &bhm LSHIFT F
            >;
        };
    };
};

Comparison to QMK​

The hold-preferred flavor works similar to the HOLD_ON_OTHER_KEY_PRESS setting in QMK. The balanced flavor is similar to the PERMISSIVE_HOLD setting, and the tap-preferred flavor is the QMK default.