All chapters
Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. Use a text editor to edit the "config.cfg" file in the "\hl2\cfg" directory. Locate the "sv_unlockedchapters" line and change its value to "15".

Get super gravity gun in any level
Enable the "map d3_citadel_03.bsp" code. Once you get the super gravity gun, enable the "changelevel [map name]" code to go to the desired level. Then, enable the "give weapon_physcannon" code.

Defend yourself by using the Zero-Point Energy gun
Take something like a barrel, chair, or another object with the Zero-Point Energy gun. Enemies cannot hurt you when they are shooting you. For better results, crouch when you are defending yourself.

Avoid losing health in Sand Trap
When you start the Sands Trap map, you will find some rocks. Someone will tell you not to step on the sand because a creature will attack. You will have to jump on the rocks. When the rock ends and only sand remains, use your gravity gun. Use it to place a door or wooden piece in the sand and stand on it. Then, place another object in front of it. Jump on it, remove the first object, and place it in front. Continue to do this until you reach rock again and the creature will not appear.

Easy kills
To kill an enemy quickly and easily, take the shotgun and hit an enemy like headcrap, zombies, and City 17 guards. Aim and hit it in the head to kill it.

Bonus sequence
After the credits, wait to see the headcrab, Lamar, being pursued by the scientist. Then, watch him pounce on your head.

Defeating Barnicals
To kill the Barnicals, let them pull you up, than hit them with a crowbar from a short distance.

Defeating Striders
If you find it difficult to hit the Striders (or any other enemy) with the RPG from far away, fire a rocket and immediately press [Zoom] (default is Z). You will automatically zoom in like normal, but will still have control of the rocket. This helps in the later levels when you do not want to get too close to the Striders, or other enemies like the Combines.

Blazing Saddles reference
When you teleport to Dr. Kliener's lab from Nova Prospekt, you will meet up with Dog and go out and find Barney. Do not follow Dog out of the lab yet; wait until Dr. Kliener and Alyx start talking about getting another headcrab to replace Lamar (Dr. Kliener's pet headcrab). After Alyx suggests that he gets another headcrab, he replies, "There is only one heady." In the movie Blazing Saddles, the villain's name is Headly Lamar (whom is called Heady Lamar by some of the characters).

Cheat Codes
Open Steam, go to your "Play Games" menu, and select Half-Life 2. Right click on it and select "Properties". Click the Launch Options button, then type "-console". Click "Ok", then close. Double click Half-Life 2 to start the game. Once it is loaded and you are playing, press the ~ key to bring up the console. Then, enter "sv_cheats 1" and press [Enter]. You can now enter the following codes at the console window. Also, any code can be used as a command line parameter by prefixing it with the "-" character. Note: For games that were downloaded from Steam, to use cheats in single player mode, start the game with the "-applaunch -dev -tconsole" command line parameter.

Map names
Use one of the following values with the "map [map name]" code:

Weapon names
Use one of the following values with the "give [item name]" code:

Item names
Use one of the following values with the "give [item name]" code:

NPC names
Use one of the following values with the "npc_create [name]" code:

Additional command-line parameters
Start the game with one of the following command line parameters to activate the corresponding feature: