This page will decode PGP armored messages in javascript. It's intended to help you debug if you happen to be working with RFC 4880 encoded messages. I built it while making dotgpg and it was inspired by (and shares code from) the awesome ASN.1 decoder.
To use it, just paste a GPG message in the box below and click Decode. On the left of the page you'll see the actual bytes, and on the right of the page is the assigned meaning.