In Art’s own words
Sentinel is the web dashboard for Natty. All posts the bot catches are sent to Sentinel, which collects them as a permanent record. The basic features of Sentinel (viewing posts, reasons, etc, as well as the statistics for them) are available to everyone, but you’ll need to sign up to access the more advanced features (post search, API access, etc).
Sentinel has two major parts
The Posts page lists all the new posts sent to the page and the Reasons page lists all the reasons due to which a particular post has been caught.
Sentinel posts receive feedback through Natty. Whenever a Natty report is given feedback to, Sentinel reflects that feedback. The feedback can be accessed through the /feedback page. The 4 types of feedback are
The source code of Sentinel is available on Github. You can raise issues or request new features there.