MUDDL (Multi-User Dungeon Design Language) is a programming language for building text-based multiplayer games known as MUDs (Multi-User Dungeons). MUDs simulate environments through textual descriptions and allow multiple users to interact in real time. The language was developed by Trubshaw, Bartle, and Taylorback in the late 1970s at the University of Essex. MUDDL was one of the first programming tools specifically designed to create virtual worlds on computers connected via networks. It influenced subsequent languages and systems for interactive fiction and online gaming.