Warpl is a simple plugin that does one thing well- warping.
There are three commands:
/warp [warpname] - Warps the player to that warp.
/setwarp [warpname] (permission node: warpl.set) - Sets a warp at the player’s location.
/removewarp [warpname] (permission node: warpl.remove) - Removes the specified warp
/warplist - Lists all the warps that exist.
I would also recommend you test your plugin in single player worlds. If you are in one world, you will be able to see you warps from another.
Hint: you should be saving the world.getUniqueId() per location so when you get your worlds list, you can verify if the world is available in the current game session.
You can see Destinations source to give you an idea of how I did it. Also, you may have issues with permissions in single player worlds, at least until this issue is solved.