The only big 'unknown' is whether Valve actually cares (hint: I'm pretty sure they don't) enough to take any action against Idle Master. I hope this insight helps! Ultimately it's up to you to decide. I have over 2,200 games in my account and if I didn't feel like this method would be safe I wouldn't have made the program in the first place. From their side of things, using Idle Master looks identical to running the game itself or using any other idling method that was previously available. The full source code is available in the OP's link so you can check yourself and see exactly what it's doing. Idle Master won't steal your Steam account details or anything shady. This required too much manual input on my part and honestly I was collecting games with cards faster than I could possibly idle them. I developed it because I had hundreds of games in my account that had card drops remaining and I was tired of the 'old methods' like using SAM to idle a game or changing a game's AppID manually and leaving it running.
