> For the complete documentation index, see [llms.txt](https://help.rails.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.rails.xyz/trading/index-and-forward-price-sources.md).

# Index & Forward Price Sources

## Index Price Source

Accurate and reliable index prices are crucial to our platform. We source index price data from multiple reputable APIs to ensure robustness, reduce the risk of price manipulation, and maintain availability. These prices underpin Rails' core services such as [funding](https://help.rails.xyz/trading/funding) and [trading metrics](https://help.rails.xyz/getting-started/trading-metrics-guide) calculations.

To ensure reliability and availability, our system uses a multi-sourced cascading fallback approach for index pricing, detailed below:

|                                                                     Primary Source                                                                    |
| :---------------------------------------------------------------------------------------------------------------------------------------------------: |
| [CoinDesk Aggregate Index API - CCIX](https://developers.coindesk.com/documentation/data-streamer/index_cc_v1_latest_tick_direct_trading_methodology) |
|                                                            Our main source of index prices.                                                           |

<table><thead><tr><th align="center" valign="middle">Backup Source 1</th><th align="center" valign="middle">Backup Source 2</th><th align="center">Backup Source 3</th></tr></thead><tbody><tr><td align="center" valign="middle"><a href="https://developers.coindesk.com/documentation/legacy-websockets/AggregateIndex">CoinDesk Aggregate Index API - CCCAGG</a></td><td align="center" valign="middle"><a href="https://hyperliquid.gitbook.io/hyperliquid-docs/for-developers/api/websocket/subscriptions">Hyperliquid Subscriptions API - Hyperliquid</a></td><td align="center"><a href="https://docs.kraken.com/api/docs/websocket-v2/ticker/">Kraken's Ticker (Level 1) API</a></td></tr><tr><td align="center" valign="middle">Used if the primary source becomes unavailable.</td><td align="center" valign="middle">Acts as a secondary fallback to maintain price availability.</td><td align="center">Acts as the last fallback to maintain price availability.</td></tr></tbody></table>

## Forward Price Source

Accurate and reliable forward prices are crucial to options valuation. We source forward price data from [Deribit’s Get Book Summary by Currency Public API](https://docs.deribit.com/api-reference/market-data/public-get_book_summary_by_currency) endpoint.

This data supports contract-level mark price and implied volatility calculations. For each live options contract, `underlying_price` provides the forward-derived price used for valuation. Options use a forward reference price in [Black-76](/trading/options/black-76-and-the-greeks.md), so this price reflects the futures curve for that expiry rather than the current spot price.