What whitelist.json is for
On an online-mode Minecraft server, the whitelist is a JSON list of player UUIDs and names. Only listed players can join when white-list is enabled in server.properties. Hand-editing that file is slow and easy to break with a missing comma or wrong UUID.
This tool lets you paste an existing whitelist, add names one per line, look up Mojang UUIDs automatically, remove stale accounts, and export a clean file. It is built for SMP openings, private friend servers, and season resets when you need a fresh allow list fast.