Library Merger is an iOS app that allows you to merge two JW Library backups. It wraps the merge logic of go-jwlm (the CLI version) into an easy to use app.
Both projects are still in beta phase, so there is a chance that you may spot a bug while using it (see A word of caution). If you want to be part of the Beta test of JWLM, feel free to join the TestFlight group here.
If you found a bug in the app, feel free to open an issue. If it might have something to do with the merge logic itself, it may be better to open the issue on the go-jwlm repository.
