I made this quickly to find domain and resource ids to use with a linode DDNS updater script, as you need the domain and resource id of the domain you want to update, and I couldn't find any easy way of finding them!
Your API isn't transmitted to my server in any way, it goes straight to the Linode API* to get information about your domains. Check the source if you don't believe me!
* The request goes though the Yahoo YQL api because the Linode API doesn't support JSONP so cross domain AJAX requests don't work
Enter your Linode API key in the field above, then click find domains. A list of your domains will then appear. Click on the Fetch Resources button on the domain which has the sub domain you want to use