# Building on Foundation

You've configured the backend. Building is turning it into an app people use — a frontend (or another
app, or an agent) that consumes what Foundation already set up: the endpoints, the auth, the data, the
components. You write what's unique; the backend is already there.

## What you build with

- **A live backend** — your entities, auth, billing, integrations, and an API, already running.
- **The SDK** (`foundation-sdk`) — one typed client for auth, data, files, integrations, account, and
  config. [Set it up](/build/sdk).
- **Built-in UI components** — login, registration, settings, plans — drop in or replace.
- **A deploy contract** — one config file and Foundation builds and hosts your app. [Deploy](/build/deploy).

## You don't have to build it by hand

Most people don't write this themselves — their agent does. Point your agent at the
[Agent toolkit](/build/agent-toolkit) and describe what you want; it uses the SDK to assemble the app.
The pages here are written so your agent has everything it needs.

## The path

1. [Set up the SDK](/build/sdk) — one initialization, shared across your app.
2. [Use your backend](/build/using-your-backend) — auth, data, files, billing from the SDK.
3. [Add the UI](/build/components) — built-in components or your own.
4. [Deploy](/build/deploy) — add one config file, ship.

Or hand the whole thing to an agent with the [Agent toolkit](/build/agent-toolkit).