Based on Ultima SDK its an Tool to view and alter almost every 2d Client file.

The application once connected to your client files allows a variety of options for visualizing the UO client data.
 ♦ Multis - Multi List with Compenent Details for each
 ♦ Animations - Animation frama data
 ♦ Items - Item List
 ♦ Land Tiles - Land Tile List
 ♦ Texture - Texture List
 ♦ Gumps - List of Available Gump Components.
 ♦ Sounds - Sound list
 ♦ Hue - Hue List
 ♦ Fonts - Client Fonts
 ♦ CliLoc - Client Localization Data
 ♦ Map - Map Data
 ♦ Light - Light Sources
 ♦ Speech - Speech Data
 ♦ Skills - Skill Data
 ♦ Animdata - Item Animation Data
 ♦ MultiMap/Facets - Multimap Data (Used for Tmaps)
 ♦ Dress - Player Body Dress Data
 ♦ TileData - Item Tile Data
 ♦ RadarColor - Color Data for Radar Visualization
 ♦ SkillGrp - Default Skill Groupings.

To Download the UO Fiddler data click here or go to the downloads section.