An API key is a key that give third-party program read-only access to your account (it means you can give your key to everybody if you don't mind showing the content of your account), you can get your key on the official Arenanet website on the application tab.

On the application page, you can create a key by pressing the New key button. Give it a name and permissions and press the create an application key button. Once the key is created you can use it on any website / application. (But I strongly recommand you to create one key per application)
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