How to install Half-Life 2 mods: Workshop, Steam releases and sourcemods

Half-Life 2 has had mods for twenty years, and the way you install one depends on how its author chose to release it. Valve's 20th Anniversary Update in November 2024 added a third route that didn't exist before. So older tutorials describe only part of the picture.

Which route does your mod use?

How it's released	Where you get it	How to install
Workshop item	The Workshop page for Half-Life 2, or in game	Subscribe, then play it from the game's menu
Standalone Steam release	Its own page on the Steam store, usually free	Install it like any game
Sourcemod	ModDB or the author's site, as a download	Extract it into the sourcemods folder by hand

The mod's page will tell you which one applies. Check that first, because the three don't overlap.

Workshop mods

The 20th Anniversary Update added Steam Workshop support to Half-Life 2. It covers more than skins: Workshop items can be entire campaigns, or replacements for weapons, enemies, sounds and UI.

Open Extras from the game's main menu to browse, install and play Workshop content without leaving the game. You can also subscribe from the Half-Life 2 Workshop in a browser, and Steam downloads the item for you.

When two Workshop replacements change the same thing, for example two different crowbar models, only one can win. If an item doesn't seem to apply, unsubscribe from the others that touch the same asset.

The same update also folded Episode One and Episode Two into the main Half-Life 2 app, so you play all three from one menu. The separate Episode apps still exist in your Steam Tools list, because some community mods are built on them.

Mods released as their own Steam game

Many of the biggest Half-Life 2 mods have their own Steam store pages. Examples include the co-op mod Synergy, which lets you play the Half-Life 2 campaigns with friends, and story mods like Entropy: Zero 2. These are the easiest of all:

1. Make sure you own Half-Life 2. Most of these releases need its content installed.
2. Install the mod from its store page.
3. Launch it from your library like any other game.

If a mod you've found on ModDB also has a Steam release, use the Steam version. Updates arrive automatically, and there's nothing to extract.

Sourcemods from ModDB

This is the classic method, and it's still how many older and smaller mods are distributed.

1. Install Source SDK Base 2013 Singleplayer. It's free and appears under Tools in your Steam library. Most sourcemods run on top of it rather than on Half-Life 2 itself. Launch it once after installing.

2. Find your sourcemods folder. On a default install it's at:

   C:\Program Files (x86)\Steam\steamapps\sourcemods\
   

   If it doesn't exist, create it. It must be directly inside steamapps, not inside common or the Half-Life 2 folder.

3. Extract the mod so that its own folder sits directly inside sourcemods. Inside that folder there should be a gameinfo.txt file.

4. Restart Steam completely by quitting it from the system tray, not just closing the window. Sourcemods only appear in your library after a full restart.

The mod then shows up in your Steam library as its own entry.

When a sourcemod doesn't appear or won't start

• It's not in the library. Check that gameinfo.txt is exactly one folder below sourcemods. Archives often contain an extra folder level, such as sourcemods\ModName\ModName\gameinfo.txt, which Steam won't detect. Move the inner folder up.
• It launches, then shows missing textures or errors about missing content. The mod needs content you don't have installed. Its page will say whether it needs Episode One, Episode Two or something else. If it needs an Episode, install that Episode's app from your Tools list.
• It closes immediately on launch. It's probably built for a different SDK base. Check the mod's page for whether it wants Source SDK Base 2013 Singleplayer, Multiplayer, or the older 2007 base, and install that one.

Classic story mods such as MINERVA: Metastasis were distributed this way. Always read the release notes for which base and content they expect.

Making your own

Valve's Source SDK tools, including the Hammer level editor, are the same ones Valve used. The Valve Developer Community wiki is the reference for mapping, modelling and scripting. Much of the documentation is old, but the Source 1 fundamentals it describes haven't changed much. A single map is a realistic first project: many well-loved Half-Life 2 releases are just that.

For Valve's VR entry in the series, which uses Source 2 and a completely separate toolset, see the Half-Life: Alyx guide.