> ## Documentation Index
> Fetch the complete documentation index at: https://ddp.drawdy.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> The Drawdy Driver Protocol and how extensions drive the Drawdy canvas.

The **Drawdy Driver Protocol (DDP)** is the contract between a Drawdy extension — a *driver* — and the Drawdy application that hosts it. A driver is a small JavaScript bundle that runs inside a sandboxed host worker and drives the canvas: it places elements, moves the camera, adds menus and panels, opens webviews, and reacts to what the user does.

This site documents that contract:

<Columns cols={2}>
  <Card title="Quickstart" icon="rocket" href="/quickstart">
    Build, run, and package your first driver in a few minutes.
  </Card>

  <Card title="Protocol reference" icon="book-open" href="/protocol/overview">
    Every command, subscription, event, and data type.
  </Card>
</Columns>

## The model

A driver never touches the Drawdy scene directly. It exchanges typed messages with the host over two channels:

* **Commands** — a request/response call from the driver to Drawdy. You ask Drawdy to do something (add elements, move the camera, read the selection) and await the result.
* **Subscriptions** — a long-lived registration. You issue a subscription command once; Drawdy then pushes **events** to your driver whenever the thing you subscribed to happens.

Both channels flow through the same envelope. A subscription is just a command whose response hands back a `subscriptionId`.

## Two guarantees

1. **Every request has a response.** Unlike LSP notifications, every command you issue resolves — with a value or an error — so the driver always knows whether Drawdy processed it. See [*LSP could have been better*](https://matklad.github.io/2023/10/12/lsp-could-have-been-better.html) for the reasoning.
2. **Requests are processed in order.** Commands sent to Drawdy are handled in the order they are received.

## What a driver looks like

A driver is a module that exports two functions:

```ts theme={"system"}
import type { DriverModule } from "@drawdy/driver-protocol";

export const activate: DriverModule["activate"] = async (ctx) => {
    // register menus, panels, subscriptions; issue commands via ctx.issueCommand
};

export const onEvent: DriverModule["onEvent"] = async (event) => {
    // react to subscription events
};
```

It is packaged as a **`.drawdyx`** file — a zip containing a `manifest.json` and the entry bundle (`main.js`, a single CommonJS file). Drawdy loads the bundle, calls `activate`, and delivers subscription events to `onEvent`.

Head to the **[Quickstart](/quickstart)** to build one.