How can I increase the key repeat rate beyond the OS’s limit?

In Windows you can set this with a system call (SystemParametersInfo(SPI_SETFILTERKEYS,...)).

I wrote a utility for myself: keyrate <delay> <repeat>.

Github repository.

Full source in case that link goes away:

#include <windows.h>
#include <stdlib.h>
#include <stdio.h>

BOOL parseDword(const char* in, DWORD* out)
{
   char* end;
   long result = strtol(in, &end, 10);
   BOOL success = (errno == 0 && end != in);
   if (success)
   {
       *out = result;
   }
   return success;
}


int main(int argc, char* argv[])
{
   FILTERKEYS keys = { sizeof(FILTERKEYS) };

   if (argc == 1)
   {
      puts ("No parameters given: disabling.");
   }
   else if (argc != 3)
   {
      puts ("Usage: keyrate <delay ms> <repeat ms>\nCall with no parameters to disable.");
      return 0;
   }
   else if (parseDword(argv[1], &keys.iDelayMSec) 
         && parseDword(argv[2], &keys.iRepeatMSec))
   {
      printf("Setting keyrate: delay: %d, rate: %d\n", (int) keys.iDelayMSec, (int) keys.iRepeatMSec);
      keys.dwFlags = FKF_FILTERKEYSON|FKF_AVAILABLE;
   }

   if (!SystemParametersInfo (SPI_SETFILTERKEYS, 0, (LPVOID) &keys, 0))
   {
      fprintf (stderr, "System call failed.\nUnable to set keyrate.");
   }

   return 0;
}