---
title: Combos
---

## Summary

Combo keys are a way to combine multiple keypresses to output a different key. For example, you can hit the Q and W keys on your keyboard to output escape.

### Configuration

Combos configured in your `.keymap` file, but are separate from the `keymap` node found there, since they are processed before the normal keymap. They are specified like this:

```
/ {
	combos {
		compatible = "zmk,combos";
		combo_esc {
			timeout-ms = <50>;
			key-positions = <0 1>;
			bindings = <&kp ESC>;
		};
	};
};
```

- The name of the combo doesn't really matter, but convention is to start the node name with `combo_`.
- The `compatible` property should always be `"zmk,combos"` for combos.
- `timeout-ms` is the length of the window (in milliseconds) in which all keys of the combo must be pressed in order to successfully trigger the combo.
- `key-positions` is an array of key positions. See the info section below about how to figure out the positions on your board.
- `layers = <0 1...>` will allow limiting a combo to specific layers. This is an _optional_ parameter, when omitted it defaults to global scope.
- `bindings` is the behavior that is activated when the behavior is pressed.
- (advanced) you can specify `slow-release` if you want the combo binding to be released when all key-positions are released. The default is to release the combo as soon as any of the keys in the combo is released.

:::info

Key positions are numbered like the keys in your keymap, starting at 0. So, if the first key in your keymap is `Q`, this key is in position `0`. The next key (possibly `W`) will have position 1, etcetera.

:::

### Advanced usage

- Partially overlapping combos like `0 1` and `0 2` are supported.
- Fully overlapping combos like `0 1` and `0 1 2` are supported.
- You are not limited to `&kp` bindings. You can use all ZMK behaviors there, like `&mo`, `&bt`, `&mt`, `&lt` etc.

:::note Source-specific behaviors on split keyboards
Invoking a source-specific behavior such as one of the [reset behaviors](behaviors/reset.md) using a combo will always trigger it on the central side of the keyboard, regardless of the side that the keys corresponding to `key-positions` are on.
:::

### Advanced configuration

There are three global combo parameters which are set through KConfig. You can set them in the `<boardname>.conf` file in the same directory as your keymap file.

- `CONFIG_ZMK_COMBO_MAX_PRESSED_COMBOS` is the number of combos that can be active at the same time. Default 4.
- `CONFIG_ZMK_COMBO_MAX_COMBOS_PER_KEY` is the maximum number of combos that can be active on a key position. Defaults to 5. (So you can have 5 separate combos that use position `3` for example)
- `CONFIG_ZMK_COMBO_MAX_KEYS_PER_COMBO` is the maximum number of keys that need to be pressed to activate a combo. Default 4. If you want a combo that triggers when pressing 5 keys, you'd set this to 5 for example.