Source SDK Base 2013 - Singleplayer andSource SDK Base 2013 - Multiplayer are necessary dependencies formods based onSource 2013. They are responsible for bootstrapping the Source engine when launching a mod and include essential parts of thesource code that are not publicly available in the official SDK. Both are available to all Steam users under the 'tools' section on the Library page. As the name implies, Source SDK Base 2013 is locked to theSource 2013 engine branch, to prevent incompatible engine updates from making mods unusable.

Since Source 2013 is split into three sub-branches, there is:

• OnSource SDK Base 2013 - Singleplayer:
  • Source 2013 Singleplayer.
• OnSource SDK Base 2013 - Multiplayer:
  • Team Fortress 2 branch - current version.
  • Source 2013 Multiplayer - legacy branch (previous2021, see below).

Tip:Despite its name, you can make a singleplayer mod usingSource SDK Base 2013 - Multiplayer, but you MUST use the legacy branch ():

• The Multiplayer branch provides additional features (static prop lightmaps,BSP compression, moreambient cubes pervisleaf, and slightly newer code).
• This may be desirable over the Singleplayer branch if not using a base mod such asMapbase and not making a single-player mod with game code untouched (this process requires you to modify the code).

Bug:TheTeam Fortress 2 branch version ofSource SDK Base 2013 - Multiplayer makes some changes which break singleplayer mode:

• save loading does not work correctly[1].
• attempting to load any map withmaxplayers andcl_localnetworkbackdoor both set to1 will crash the game[2] (not affected when running on 32-bit).

SDK Base versions

There are two versions of Source SDK Base 2013:

• Source SDK Base 2013 - Multiplayer (AppID:243750 -Click to Install)

Note:This branch originally ran onSource 2013 Multiplayer, but it has been upgraded to theTeam Fortress 2 branch, which might be incompatible with mods built on the legacy version ofSource SDK Base 2013 - Multiplayer (that runs onSource 2013 Multiplayer).
To downgrade to legacy version of Source SDK Base 2013 Multiplayer, follow the instructions:

1. Open Steam, go toSource SDK 2013 Multiplayer, right click Properties
2. A window will open. Go to "Betas", selectprevious2021 beta branch.
3. Steam will automatically re-download the files. Once it's done, run Source SDK Base 2013 MP as normal, or use its tools.

• Source SDK Base 2013 - Singleplayer (AppID:243730 -Click to Install)

Note:By default, manysourcemods (includingMapbase), will crash when launched, unless you select theupcoming branch.
To selectupcoming branch, follow the instructions:

1. Open Steam, go toSource SDK 2013 Singleplayer, right click Properties
2. A window will open. Go to "Betas", selectupcoming beta branch.
3. Steam will automatically re-download the files. Once it's done, try to launch the mod again.

Important:As of October 2025, unlikeHalf-Life 2,Portal andHalf-Life: Source,Source SDK Base 2013 Singleplayer hasn't been updated since 2015, and doesn't include any new features fromHalf-Life 2's 20th Anniversary Update orTeam Fortress 2 branch (such asradial fog, classic particles, etc.) aswell asbug fixes introduced with later version ofHalf-Life 2 (and other Source games).
The latest version of Source SDK Base 2013 SP are from June 2014, whileupcoming branch was last updated in September 2014. Gamecode for the SP branch was last updated in September 2015.

Setting up & compiling code

To set up Source SDK 2013 and compiling mods, see:

• Setting up Source SDK Base 2013 Multiplayer - forTeam Fortress 2 branch (using post-2025Source SDK Base 2013 - Multiplayer)
• Setting up Source SDK Base 2013 Singleplayer - forSource 2013 Singleplayer (usingSource SDK Base 2013 - Singleplayer)
  • Source code for this SDK is not yet updated, unlike the TF2 branch, and will require using an older version of Visual Studio or GCC to compile.
  • Also applies to legacy (pre-2025) version ofSource SDK Base 2013 - Multiplayer.

SDK Base Content

Singleplayer branch

• Source Engine Test (sourcetest)
• Half-Life 2: Episode Two shared (ep2)
• Half-Life 2: Episode One shared (episodic)
• Half-Life 2 shared (hl2)
• Source 2013 Singleplayer branch (32-bit binaries only)

Multiplayer branch

• Source Engine Test (sourcetest)
  • Note:Source Engine Test can only be launched with 32-bit binaries.
• Half-Life 2: Deathmatch shared (hl2mp)
• Half-Life 2 Complete (hl2_complete)
• Half-Life 2 shared (hl2)
• Team Fortress 2 branch (32/64-bit binaries)

Known issues

If there are any issues or bugs with Source SDK 2013, including SDK Base, search for existing bugs or report it here on GitHub:

• Source SDK 2013 - GitHub Issues

• Pages with uncategorized bugs
• Tools
• Source
• SDK 2013
• Source SDK FAQ
• Source 2013 SP engine branch games
• Team Fortress 2 branch games

• English