Terrasavr is a web-based Terraria profile/inventory editor.
It allows user to upload their Terraria character (also called player or profile) file,
perform operations over it
(such as modifying it's looks, adding/removing items and buffs, etc.),
and save it back to disk for later use in-game in single-player or multi-player modes.
Terrasavr works with latest version of Terraria, but can also load and save player files made
by earlier versions of the game, meaning that it can be used to migrate savegames back and forth
between game versions.
Due to web-based nature, Terrasavr is used explicitly online, without having to download or install any software. It also works on all major operative systems and browsers, including Windows, Mac, and Linux.
(or try the flash version).