A mudlib, short for mud library, is a library of code forming part of the technical infrastructure of a MUD. Though different varieties of MUD may be considered to have mudlibs, the term is most often used with LPMuds. In an LPMud, the mudlib consists of interpreted code written in the LPC language, which is interpreted on the fly by a driver. The driver acts as a virtual machine while the mudlib acts as an operating system by defining how the world acts and controlling its processes.
Publicly available LPC mudlibs include:
- CDlib
- Dead Souls
- Lima
- Sapidlib, also known at one time as the LPUniversity Mudlib
- Nightmare
- TMI
An example of a non-LPC MUD with a clearly identifiable mudlib is MUME, a DikuMUD that implements global support code in its language Mudlle.