Source SDK
The Source SDK provides the source code and tools for creating Source engine mods. It was first released on November 5th 2004. In 2013 the source code was moved to GitHub at https://github.com/ValveSoftware/source-sdk-2013. The Valve-ERC forums hosted by Chatbear at http://www.chatbear.com/unity2/9/unityhome contained Source modding forums but they were closed in favour of the Steampowered User Forums, which were themselves shut down, though an archive remains at https://archive.org/details/steamforums_spuf_archive_201706.
Faceposer
Faceposer currently does not work on operating systems other than Windows XP due to a dependency on the Microsoft Speech API 5.1. A fixed phoneme extractor has been created to work around this (v1.2 and v1.3). It can also reportedly be fixed by copying the bin/lispinc_data and bin/phonemeextractors from Source Filmmaker and then opening the Phoneme Extractor window and clicking "Change Speech API" and choosing "Lispinc Speech API".
vice
vice allows the encryption and decryption of files. Various script files can be encrypted to prevent easy modification, though the encryption key necessarily must ship in the game code, so it is not meant to provide absolute security. vice uses ICE encryption. It has been used to encrypt .txt and .nut files into .ctx and .nuc files.
vtex
vtex is a tool to convert .tga files into .vtf files. It accepts a .tga and an identically named .txt file with parameters and outputs a .vtf file. Unlike other tools in the Source SDK, vtex is not open source - possibly some of the DXT compression algorithms are proprietary.
64-bit support
The Source SDK is 32-bit but Blade Symphony ships with some 64-bit Source SDK tools.
Third-Party Tools
| Tool | Use | Link |
|---|---|---|
| AutoMDL | Model compilation tool | https://github.com/NvC-DmN-CH/AutoMDL |
| AutoVTF | Texture compilation tool | https://github.com/NvC-DmN-CH/AutoVTF |
| Hammer++ | Map creation tool | https://ficool2.github.io/HammerPlusPlus-Website/ |
| hlmv++ | Model compilation tool | https://github.com/ImguRandom/HLMVPlusPlus |
| Slammin' Source Tools | Map compile tools | https://knockout.chat/thread/992 |
| SourceIO | Blender plugin | https://github.com/REDxEYE/SourceIO |
| VTFEdit-Reloaded | .vtf viewer | https://github.com/Sky-rym/VTFEdit-Reloaded |
| Wall Worm | 3ds Max plugin | https://dev.wallworm.com/ |