The Plate Theme Tool starts up a listener for your theme’s folder, and tracks changes. When a file is changed (added, edited, deleted), the theme tool uploads the change immediately to Plate’s servers. This way you don’t have to worry about FTP’ing your files after each change, but you can edit your theme or site’s theme files on the fly.
Fill in your API key and click ‘Verify’. You can find your API credentials in your User settings in the Plate dashboard.