# Building Bits: the full context for an agent This document is the whole of what an agent needs to know to build a Bit that is perfectly at home on Rabbit. It describes the environment a Bit runs in, the APIs Rabbit installs into it, how Rabbit reads and presents the document, and the lines that cannot be crossed. Everything here comes from the running platform. Where this document says something works, the code supports it; where it says something is blocked, the sandbox blocks it. Rabbit is where a creator keeps what they build with AI and hears back from the people they send it to. A **Bit** is one thing on Rabbit: a small, self-contained interactive creation, a game, a toy, a tool, a visualization, a tiny site. Most Bits are one HTML document that Rabbit hosts, and nearly all of this guide is about those. A Bit can also be a page hosted anywhere else and added as a link; it stays where it is, and section 3 says the one part of Rabbit it can still reach. The person asking for one is usually not technical. The deliverable is always something finished and playable, never a scaffold or a demo. ## 1. What a Bit is, physically - Exactly one complete HTML document. Starts with ``, ends with ``. No markdown fences or commentary before or after. - At most 2 MB (`2 * 1024 * 1024` bytes). This is a hard gate: a document over it is rejected before it can be posted. Aim far under; most great Bits are tens of kilobytes. - Must parse as HTML: a doctype or at least one real element of its own. A text file renamed `.html` fails the gate. - Fully inline, with one exception for the font. Styles in `