You can create an API-Key for your account at https://account.arena.net/applications.
Key must have progression perms, as seen in the image below.
The GW2 API gives in-game info, see the wiki page: https://wiki.guildwars2.com/wiki/API:Main
This web-site only uses Achievement Information from your account, to show you which Jumping Puzzles you have completed.
When you submit a key, it is saved and loaded when you return.
Your key is kept private, since it not sent to the server. (Unless you choose to share it.)