MUDDLE is an object-oriented language, supporting inheritence from multiple sources and using a directed pattern-matching algorithm (like an hierarchical version of Prolog's unification). Although primarily intended for use in text-based adventures (its parser is perhaps the most powerful of all those used by MUDs), MUDDLE is nevertheless sufficiently flexible that it can be used for other games, or indeed for non-games (the MUDDLE interpreter could be written in MUDDLE!). It is not merely a database; it really is a full-fledged programming language - manuals, primers and all.

Because MUDDLE is MUSE's bread and butter, licences to use it are very tightly specified and not at all cheap: an unlimited licence is £30,000. Smaller-scale licences for specific, individual products are less expensive, and occasionally individual developers may be granted a licence at a knock-down price for a share of the royalties on games implemented in MUDDLE, although this is rare.

MUDDLE may seem expensive, but the alternative - designing, programming and debugging something which would take a team 6 to 12 months to complete and still probably be inferior or unsuitable - will work out costing considerably more.