Form fill

Charm can already do this, using Text Replacement. It lets you set a short shortcut that expands into any longer text you like, such as your full address.

How to set it up:
1- Open Charm's Settings and go to Personal, then Replacements.
2- Add a shortcut (for example addr) and set its expansion to your full address.
3- Now, in any app including web forms, type addr and Charm expands it to the whole address.

This works in normal form fields just like anywhere else. The only spots Charm deliberately leaves alone are password fields and the browser's address bar, so your saved snippets are there when you need them. Add as many as you like (email, phone, a standard signature), all kept on your Mac. Give it a go and let us know how you get on?