Hot on the heels of last week's announcement that Valve was turning its multiplayer shooter -- Team Fortress 2 -- into a free-to-play product, it's been revealed that Valve will soon release the Source Engine SDK mod tools for everyone to use for free. At the moment you can only access the Source Engine SDK by paying for a Source Engine based game but with last week's change of Team Fortress 2 into a free game, Rock Paper Shogun reports that Valve has now made the decision to make the mod tools free as well.
According to an email from Valve's Robin Walker, "We are in the process of getting it all done. It’s a bit messy because we have multiple versions of the SDK, and there’s some dependencies we need to shake out. But yes, the gist of it is that we’re just going to go ahead and make the Source SDK freely available." The tools included in the Source SDK include the Hammer level editor, a model viewer and more. You can get more info on the Source Engine SDK via Valve's developers web site.
While the Source Engine SDK will soon be free, it looks like amateur game developers will still require that a Source Engine game be installed before playing any mods created via the Source Engine SDK, even if Team Fortress 2 and another free game, Alien Swarm, are free. This is in contrast to Epic Games' UDK which allows people to create stand alone games using a modified version of Epic's Unreal Engine 3.