Today I learned about the existence of keyd, which is a system-wide daemon program that lets you remap keys on a kernel level.

I previously used kmonad, but its configuration file can be overwhelming to setup for simple needs. Keyd feels simpler and has a minimalistic configuration syntax.

In author's words:

Notably keyd was written entirely in C with performance and simplicitly in mind and will likely never be as configurable as kmonad (which is extensible in Haskell).

Here's how my current configuration looks like:

[ids]
0001:0001

[main]
shift = oneshot(shift)
control = oneshot(control)
leftalt = oneshot(meta)
leftmeta = oneshot(alt)
capslock = overload(C, esc)
f = overload(extend, f)
v = overload(number, v)

[extend]
h = left
j = down
k = up
l = right
y = home
u = pagedown
i = pageup
o = end
m = enter
; = backspace

[number]
m = 1
, = 2
. = 3
j = 4
k = 5
l = 6
u = 7
i = 8
o = 9
; = 0

What it does:

• turns all modifier keys into "one-shots", meaning they stick until next keypress so you don't have to hold them down;
• swaps left alt and meta (cmd) keys;
• capslock becomes esc on tap and ctrl on hold;
• holding f activates the "extend" layer with navigation keys on the home row;
• holding v activates the "number" layer with numbers arranged into a numpad on the home block.

Unfortunately, keyd is Linux-only. If you're interested in a cross-platfom solution, check out kmonad.