Syster is a way to input symbols in a different way: instead of macros, Leader sequences or the like, we trigger the special input mode, and enter the symbol’s name. Once finished, we hit Space, and this plugin will do the rest: delete everything we typed, look up an action for the entered symbol, and execute that.

There are a number of ways this can be useful, but the easiest showcase is symbolic Unicode input: SYSTER coffee SPACE turns into , with just a little code.

Using the plugin

To use the plugin, one needs to include the header and set up a function that will handle the symbol actions:

#include <Kaleidoscope.h>
#include <Kaleidoscope-EEPROM-Settings.h>
#include <Kaleidoscope-HostOS.h>
#include <Kaleidoscope-Syster.h>
#include <Kaleidoscope-Unicode.h>

void systerAction(kaleidoscope::plugin::Syster::action_t action, const char *symbol) {
  switch (action) {
  case kaleidoscope::plugin::Syster::StartAction:
    Unicode.type (0x2328);
  case kaleidoscope::plugin::Syster::EndAction:
    handleKeyswitchEvent (Key_Backspace, UnknownKeyswitchLocation, IS_PRESSED | INJECTED);
    handleKeyswitchEvent (Key_Backspace, UnknownKeyswitchLocation, WAS_PRESSED | INJECTED);
  case kaleidoscope::plugin::Syster::SymbolAction:
    Kaleidoscope.serialPort().print ("systerAction: symbol=");
    Kaleidoscope.serialPort().println (symbol);
    if (strcmp (symbol, "coffee") == 0) {
      Unicode.type (0x2615);


void setup() {
  Kaleidoscope.setup ();

Note that we need to use the Syster object before any other that adds or changes key behaviour! Failing to do so may result in unpredictable behaviour.

Plugin methods

The plugin provides the Syster object, with no public methods. There are two methods outside of the object, however, that can be overridden:

systerAction(action, symbol)

Called whenever an action needs to be taken, which can happen in three cases:

First, when the Syster key is pressed and the alternate processing starts. In this case, action will be set to kaleidoscope::plugin::Syster::StartAction, and symbol will be NULL. This function can be used to do some setup to make it more obvious that the Syster input mode is active, such as sending a Unicode symbol to the host, or lighting up LEDs, or anything else we’d like.

Second, when the sequence is finished with a Space. In this case, action will be set to kaleidoscope::plugin::Syster::EndAction and symbol will be NULL. This can be used to undo anything that the start action did, if need be.

Third, when the action for the symbol should be made. In this case, action is set to kaleidoscope::plugin::Syster::SymbolAction, and symbol will be a C string. It is up to us, what we do with this information, how we handle it.


A function that turns a keycode into a character. If using QWERTY on the host, the default implementation is sufficient. When using something else, you may have to reimplement this function.


Further reading

Starting from the example is the recommended way of getting started with the plugin.