Games giant Valve has added the full client and server code for Team Fortress 2 to its Source engine SDK. 

In a blog post, the company said that this will allow developers to create brand new game mods if they want to. Fans will now be able to "change, extend or rewrite" the online shooter. 

Game creators, however, cannot profit from their creations. 

"The SDK is licensed to users on a non-commercial basis, meaning that any mod created using the SDK must be free, and any content in those mods must be free. TF2 mods may be published on the Steam Store, and after publication will appear as new games in the Steam game list," Valve wrote.

"Players have a lot of investment in their TF2 inventories, and Steam Workshop contributors have created of a lot of that content. The majority of items in the game now are thanks to the hard work of the TF2 community. To respect that, we're asking TF2 mod makers continue to respect that connection, and to not make mods that have the purpose of trying to profit off Workshop contributors' efforts. We're hoping that many mods will continue to allow players access their TF2 inventory, if this makes sense for the mod."