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

# SDK overview

> Choose an official SDK for your application.

Official SDKs provide typed or idiomatic wrappers around the Billions public API.

<CardGroup cols={2}>
  <Card title="TypeScript SDK" icon="js" href="/sdks/typescript">
    For Node.js and TypeScript applications. Published as
    `@billions-works/sdk-ts`.
  </Card>

  <Card title="PHP SDK" icon="php" href="/sdks/php">
    For PHP 8.1 and newer. Published as `billions-works/sdk-php`.
  </Card>
</CardGroup>

Both SDKs default to:

* API host: `https://api.billions.works`
* Public API version: `v1`

## Shared concepts

The SDKs preserve public API field names such as `order_no`, `invoice_url`, and
`expires_at`. Both support idempotent invoice creation and invoice lookup by
order number.

Choose the SDK matching your backend runtime. API keys must never be used in
frontend or mobile client code.