GoldSrc (also known as "Goldsource" or "Half-Life engine") is the game engine on which Half-Life (and several games related to it) runs on.

Origin of the name

"GoldSrc" was the internal codename for the Half-Life engine during the later stages of its development, when the engine code was forked into a development branch and a stable branch. Half-Life was released with the GoldSrc engine code, and the non-gold "Src" became known officially as Source, which would eventually be the engine used by Half-Life 2.

Technology

GoldSrc is a heavily modified version of the Quake engine and thus inherits some traits from it. Some systems were written from scratch by Valve like the artificial intelligence (AI) based on tasks & schedules, the skeletal animation system and much more. GoldSrc also reuses some code from QuakeWorld (update for Quake primarily designed for better networking play) and Quake II but only in small amounts.

Valve acquired Worldcraft and developed Valve Hammer Editor, the level design tool we know today to create maps for Half-Life.

Post-release, Valve updated GoldSrc to add features such as client-side prediction in multiplayer, the transition from the WON network platform that was shut down to Steam, and much more.

In 2013, the GoldSrc engine was ported to OS X (long before Apple made the call to replace Intel x86 processors by their custom M-series ARM processors) and a Linux client was made available (previously, only dedicated servers could run on Linux). Some people also refer to this update as "SteamPipe update".

GoldSrc has received some updates since, although those are more "quality of life/security" related rather than content related.

To celebrate Half-Life's 25th anniversary, Valve released a major update in late 2023. Noteworthy changes include the addition of Half-Life: Uplink (a demo), multiplayer maps, better controller/gamepad support (including Steam Deck), Peer-2-Peer (P2P) thanks to Steam Networking, HUD scaling, the original WON main menu and many small changes. This update is nicknamed "HL25".

Games

Notable games/mods running on the GoldSrc engine developed by Valve itself includes:

• Half-Life
• DeathMatch Classic
• Team Fortress Classic
• Ricochet

Several known community-made mods were released which Valve took interest in and hired its developers as well as acquiring them:

• Counter-Strike
• Day of Defeat

Several other video game companies were allowed to develop games/mods on the GoldSrc engine, those are:

• Half-Life: Blue-Shift (Gearbox Software)
• Half-Life: Decay (Gearbox Software - PlayStation 2 exclusive)
• Half-Life: Opposing Force (Gearbox Software)
• Gunman Chronicles (Rewolf Entertainment)
• James Bond 007: Nightfire (Gearbox Software - Mac OS and Windows versions)
• Counter-Strike Neo (Namco - Japanese arcade exclusive)
• Counter-Strike: Condition Zero (Ritual Entertainment & Turtle Rock Studios) also includes the "Deleted Scenes"
• Counter-Strike Online (Nexon - Asia exclusive)
• Counter-Strike Nexon: Studio (Nexon) previously known as Counter-Strike Nexon: Zombies

In the past, Valve exceptionally allowed two community-made mods access to the entire engine and authorized them to be released as "standalone" projects. Those are "Sven Co-Op", a co-operative multiplayer experience for Half-Life and "Cry of Fear", a psychological survival-horror experience.