LSL

LSL, the Linden Scripting Language, is a scripting language used in Second Life to give in-world objects, features, and avatars interactive behavior. Scripts run on the simulator and are attached to prims, objects, or avatars to respond to events and perform actions, enabling everything from simple animations to complex systems.

LSL is designed as an event-driven, procedurally oriented language with a C-like syntax. It is statically typed and provides data types such as integer, float, string, key, vector, rotation, and list. Programs are organized into states, with a default state containing the state_entry event; objects can react to events such as touch_start, collision_start, on_rez, timer, and listen-related events. The language supports common control structures (if/else, while, for, switch) and a rich standard library of built-in functions.

Most functionality in LSL is exposed through a large set of built-in functions prefixed with ll, covering object manipulation (llSetPos, llSetRot, llSetText), communication (llSay, llWhisper, llListen), sensing and interaction (llSensor, llGetMcEvent), and external connectivity (llHTTPRequest). LSL also supports data structures such as lists and strings, enabling developers to create complex interactions, games, and automation within the virtual world. Scripts are subject to memory limits (historically around 64 kilobytes per script) and operate with restricted access to the hosting environment, notably lacking direct file I/O or local system access.

Developers use LSL to create interactive objects, NPC behaviors, and gameplay mechanics, contributing to the broader ecosystem of Second Life content. While closely tied to Second Life, LSL concepts and some compatibility have influenced similar scripting environments in other virtual worlds.