> ## Documentation Index
> Fetch the complete documentation index at: https://docs.d1.exchange/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> Integrating with D1.

D1 is an options exchange. It lists cash-settled options on crypto underlyings, quoted and settled in USDC, and runs a central limit order book for each market.

D1 is the system of record for everything an integration needs to agree on: instruments, orders, fills, balances, positions and settlement. External systems connect to D1 over versioned HTTP APIs.

## Documentation

> [card] [Market Makers](https://docs.d1.exchange/market-makers/introduction.md)
>
> Integration guides for teams providing liquidity on D1.

> [card] [API Reference](https://docs.d1.exchange/api-reference/introduction.md)
>
> Exact request and response schemas for every public endpoint.

If you are a market maker with a D1 API key, start with the [Quickstart](https://docs.d1.exchange/market-makers/quickstart.md). It takes you from your key to a placed, reconciled and cancelled order.


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