Half-Life Cheat Codes

Note:  The God mode and Noclip cheats do not work in the demo version of Half-Life (Uplink). All cheats do work in the Uplink lite version of the demo (which requires the retail version installed). Note that cheating in the single-player game may mess up some of the scripted sequences and make it so you don't see everything you would if you weren't cheating (such as you never wake up after being captured on the Apprehension episode, or the final boss emits ligtning forever and refuses to die). I suggest trying the Half-Life Walkthrough (or the Opposing FOrce Walkthrough) before cheating if you you're having trouble making it through the single-player game. If you must cheat, just enable cheats long enough to get past a problem area and then disable them again before continuing or saving your game.

Enabling Basic Cheats
Load the game with the " -console" command-line option ("hl.exe -console" -- see the detailed instructions on the Console Help page if you don't know how to do this). Start a new game, and then open the console (either hit ESCAPE to return to the main menu and select "console", or press ~ -- the tilde key), and type sv_cheats 1 and press enter. Next enable developer mode by typing developer 1 and then pressing enter. You can automate all of this by using the following command-line to load Half-Life: hl.exe -console -dev +sv_cheats 1 (note the spaces before '-', '+', and '1', those are required). By the way, there are many other command-line flags like -console and -dev for various purposed (I use -numericping and -toconsole), and they are all listed here. As shown in the exanmple above (+sv_cheats 1), you can also set any console variable on the command-line by adding a plus (+) followed immediately (no space) by thwe variable name, then a space and the value you want to set the variable to. Multiple command-line flags and variable settings may be chained together in any order as long as you separate each with a space. 

Before using any of the cheat codes listed below, load a saved game, start a new one, or simply open the console and type map mapname (see the walkthrough for Half-Life or Opposing Force for the valid mapnames). If you're cheating and you are still trying to complete it for the first time, be sure to disable cheats before saving a game or playing the "Apprehension" or "Nihilanth" Half-Life episodes. These episodes (and possibly some others) do not always play correctly when cheats are enabled (scripted sequences appear to hang). If you have problems moving from one episode to another, or if you see bug in the scripted actions in the game, try disabling cheats before playing that part. 

Disabling Basic Cheats
Open the console and turn off developer mode (type developer 0 and press enter), then turn off cheats (type sv_cheats 0 and press return). If you get tired of typing that, note that you can make one key do it all for you by binding a key as in: bind x "developer 0; sv_cheats 0". You could even make a special quicksave key that disables cheats before saving your game, as in: bind x "developer 0; sv_cheats 0; save quick". Of course, you can change 'x' to any key or button you like. See the Console Guide for more details. 

Problems With Cheats
I have heard a few reports that the /give cheat will not work until after you've reached a new "chapter" in the story (when the white text, i.e. "Unforeseen Consequences" appears on screen then fades away), or that the /impulse 101 cheat doesn't work properly. I have not been able to duplicate this problem with any version of Half-Life. 

Note that it's your HEV suit (PCV in Opposing Force) that provides your HUD (Heads-Up Display) that shows your weapon selection, ammo and health status, etc. If you don't have a suit (cheat code /give item_suit, see below), you won't see any HUD, so you can't tell if the cheats are working correctly. Before using any other /give cheats or /impulse 101, be sure to give yourself the suit (and the crowbar: /give item_crowbar). 
 

Cheat Codes
Type any of these into the console after doing the above:

/GOD - god mode. 
/NOCLIP - walk through walls/fly. 
/MAP xxxx - go to map xxxx. Map names are of the format c#a#, (c1a1, c2a1, etc). Will screw up 1p game script sequences. 
/IMPULSE 76 - "Grunt-O-Matic" - spawn a grunt on any map. You must first set sv_cheats, developer, and mp_allowmonsters all to '1', then quick save/load before spawning.
/IMPULSE 101 - give all weapons and ammo, so say DaGimp. David says you need to enter this command at least four times to get the bigger weapons fully loaded. Some people swear you need the slash (/), some say you don't. This seems to work for most people, but a few have problems. I have no idea why this may or may not work for you (it does for me), so please don't email me and ask. Try exiting and reloading, or making a shortcut to Half-Life that includes " +sv_cheats 1" on the command-line properties. (Don't forget the space before the plus).
/GIVE xxxx - give item xxxx. This seems to work for most people, but a few have problems. I have no idea why this may or may not work for you (it does for me), so please don't email me and ask. The following items are available for Half-Life or Opposing Force (weapon_gauss, weapon_glock, and weapon_python don't work in OpFor): 
 

item_airtank ammo_357 weapon_357
item_antidote ammo_9mmAR weapon_9mmAR
item_battery ammo_9mmbox weapon_9mmhandgun
item_healthkit ammo_9mmclip weapon_crossbow
item_longjump ammo_ARgrenades weapon_crowbar
item_security ammo_buckshot weapon_egon
item_sodacan ammo_crossbow weapon_gauss
item_suit ammo_egonclip weapon_glock
ammo_gaussclip weapon_handgrenade
ammo_glockclip weapon_hornetgun
ammo_mp5clip weapon_mp5
ammo_mp5grenades weapon_python
ammo_rpgclip weapon_rpg
weapon_satchel
weapon_shotgun
weapon_snark
weapon_tripmine

Opposing Force
The Opposing Force addon for Half-Life adds quite a few new weapons. The codes for these weapons are listed below (the ammo and item names will be added as soon as I can find them -- if you know, please send them in.) 
 

weapon_displacer
weapon_eagle
weapon_grapple
weapon_knife
weapon_m249
weapon_pipewrench
weapon_shockrifle
weapon_sniperrifle
weapon_sporelauncher ammo_spore

Advanced Cheats
The cheats explained above should be enough to get you out of any tough spots that the Walkthrough can't help with. If you want to try some really interesting new cheat codes for playing around with the characters and enemies in Half-Life, see the Advanced Cheats Page