Polar supports synchronizing the storage of your documents and annotations (known as our datastore) with the cloud and synchronizing data across computers.
Cloud storage is near real-time and actively pushes updates to your other devices so that when you change computers your documents are already up to date - no waiting (assuming your computer is active at the time).
Polar Cloud storage is backed by Google's Firebase. You can read about the design in this blog post in the Cloud storage infrastructure.
All documents in Polar are only available to your account and we use Google Firebase access control credentials to block unauthorized users (anyone other than you).
Every new user gets 1 GB of cloud storage for free. Higher tiers provide you with up to 500 GB storage. See details here