Start the game with the -DEVMODE command line parameter. Then, press one of the following keys during game play to activate the corresponding cheat function. Note: When in developer mode, all levels will also be unlocked.

Effect - Key

Spawn point [F3]
All weapons P
999 ammunition O
Toggle no clipping [F4]
Move to next checkpoint [F2]
Save current position [F9]
Load current position [F10]
Toggle extra information [F11]
Toggle first and third person view [F1]
Toggle God mode [Backspace]
Increase speed [Equals]
Decrease speed [Minus]
Return to Default speed [F5]