"Tim obviously wasn't thinking that you might be modifying the hosted files directly with the same device that you are doing the sync."   Actually, I was. And while developing EasySync, that's exactly what I was doing: Using my workstation as if it were a mobile device, updating records on it, and with it to update records directly on the host.   The Device ID concept was added specifically to address the "round trip" issue. You wrote, "Because I usually push up a minor amount of data it's a minor problem that if what I push up also gets pulled back down, i.e. roundtrips." For many, it is a huge issue. Imagine that you've pushed up several photos or other binary data in container fields. "Round tripping" that data can easily become a nightmare.      "...but I'm not good enough to write that statement and maybe neither was Tim."   I'm not sure what to make of that. A lot of work went into making EasySync work as seamlessly as it does. The level of abstraction involved to pull that off was insane.     I made EasySync an open source solution for several reasons.   The primary reason was to share it with the community, and provide a sync framework that was easy to implement and extremely affordable (you can't beat "free"). Sync support is a critical feature for many mobile solutions. In fact, not having it can be a show stopper in some cases. My hope was that EasySync would help developers meet that need, sell more FileMaker Go-based solutions, and help the FileMaker platform in general.    But another reason for making it open source was to provide code that was fully unlocked and easily modifiable to meet specific needs. If you don't need the Device ID, and if round tripping isn't an issue for your solution, then disable it.    - Tim