To input the following cheats you have to enable the console interface in the single-player game. To do this, make a shortcut of hl.exe, and then add -dev -toconsole to the command line. Start Half-Life with this shortcut.

Half-Life will load directly to the console interface, bypassing the opening flash screens. If you already have a quick-saved game, hit the F7 key. If you are starting a new game type map c0a0 (these are zeros) into the console to start with the train ride introduction, or map c1a0 (again, a zero) to start after the train ride introduction.

The console is now active in single-player mode and you can input the cheats. Standard Quake cheats such as GOD, FLY, NOCLIP, and NOTARGET are now available, as are the Half-Life-specific cheats listed below.

To enable a cheat, type /GIVE X where X is any of the following codes. For example, typing /GIVE WEAPON_SHOTGUN will give you a shotgun.

Cheat Codes
ITEM_AIRTANK
ITEM_ANTIDOTE
ITEM_BATTERY
ITEM_HEALTHKIT
ITEM_LONGJUMP
ITEM_SECURITY
ITEM_SODACAN
ITEM_SUIT AMMO_357
AMMO_9MMAR
AMMO_9MMBOX
AMMO_9MMCLIP
AMMO_ARGRENADES
AMMO_BUCKSHOT
AMMO_CROSSBOW
AMMO_EGONCLIP
AMMO_GAUSSCLIP
AMMO_GLOCKCLIP
AMMO_MP5CLIP
AMMO_MP5GRENADES
AMMO_RPGCLIP
WEAPON_357
WEAPON_9MMAR
WEAPON_9MMHANDGUN
WEAPON_CROSSBOW
WEAPON_CROWBAR
WEAPON_EGON
WEAPON_GAUSS
WEAPON_GLOCK
WEAPON_HANDGRENADE
WEAPON_HORNETGUN
WEAPON_MP5
WEAPON_PYTHON
WEAPON_RPG
WEAPON_SATCHEL
WEAPON_SHOTGUN
WEAPON_SNARK
WEAPON_TRIPMINE

Tip: You're not the only one fighting aliens; the commandos are, too. If you find yourself in a situation that has both aliens and commandos in the same area, pick a nice hiding spot and watch them beat up on each other. When the fighting stops, jump in and finish off the weakened winner.

Tip: Use security guards as backup. Get up real close to them, and press your "use" key until they say something to the effect of, "You're right, we'll have a better chance together." Once they're following you, they'll engage aliens and commandos at will.

Tip: Commandos are very smart, and once your position has been compromised, it's on! Not only will they attack you in formation but they'll also lob grenades at you. So don't sit still. A veteran friend of mine once told me that the only way to survive an ambush is to run into it, and the same holds true in Half-Life. Sure, the odds will still suck, but they'll suck less.

Tip: If you find yourself hurting and in desperate need of medical attention, seek out a scientist. Walk up to him and press your "use" key until he says, "Let me take care of that wound for you." This won't work every time, but when it does, it's a welcome surprise.