ChatterBox is a userscript that adds an inbox checker to the StackExchange Chat interface.
ChatterBox requires userscript support, which means you'll need GreaseMonkey on Firefox. It is supported natively in Chrome, and is untested on Opera.
Your access token is:
I don't want the token to expire. Request new token
Once you've requested a token, press the "Inbox" and then the "Config" button in chat, and copy and paste your token into the "Access Token" blank and hit "Save." Press the "Inbox" button and you should see your inbox items. Normally, tokens expire after 24 hours, but you can request one that does not expire by checking the "I don't want the token to expire" button above.
If you decide you don't want to use this anymore, you can delete the access token from the configuration and hit save to clear it out.