Half-Life and Steam creator Valve have announced that the company's Source Engine and modding tools will now be made available completely free of charge.
The software development kit (SDK) for the technology was previously only available after the purchase of a Valve game, but following the move to make Team Fortress 2 free-to-play the SDK has now also been made available at no charge.
Valve's Robin Walker has admitted that the free availability of the SDK was not originally planned and was an unintended side benefit of the change in Team Fortress 2's business model.
After a fan pointed out the loophole Walker revealed to website Rock, Paper, Shotgun that Valve decided not to limit the availability, but that the company had not planned in advanced for it.
"We are in the process of getting it all done," he said. "Its a bit messy because we have multiple versions of the SDK, and theres some dependencies we need to shake out. But yes, the gist of it is that were just going to go ahead and make the Source SDK freely available."
More information is available at the official website, although it still refers to the SDK as being only available with a purchase of a game.