The Powder Toy Lua API is a set of objects and functions that was introduced in version 83 (The TPT++ Release). They allow control over some aspects of the game, including graphics, element interactions and interfaces.

boxmein made an massive reference of the most parts of the API, including these not added to this wiki yet. You can find it here.

The API is split into several categories

Interface

Includes UI components such as buttons, labels and checkboxes, access to the very primitive window manager and input events

Renderer

Methods and constants for interacting with the display mode

Elements

Methods and constants for modifying and creating elements

Simulation

Methods for modifying the state of the simulation

Graphics

Methods for drawing simple shapes and text on screen.

File System

Functions for creating, deleting, modifying and enumerating files and folders.

Bit

Doesn't actually provide any interaction with the game, but provides some functions for performing bitwise operations on integer numbers.

Legacy

Old Lua API with the tpt.* prefix