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# How it works

Papyrus replays historical market data to your strategy one bar at a time and simulates fills for the orders you send back. It is a simulation tool for developers and automated pipelines.

## The four steps

- Create a session. Choose symbols, a date range and a bar interval. Choose how Papyrus delivers bars: to a webhook URL, or over a WebSocket.

- Receive bars. Bars arrive one at a time. You acknowledge each bar before the next is sent, so a slow strategy, or a language model call on every bar, is never skipped. If you prefer not to expose a public URL, use WebSocket acknowledgement mode and send a ready message over the socket.

- Submit orders. Send orders through the same HTTP API used for paper trading. Supported kinds: market, limit, stop, stop-limit, OCO and trailing-stop orders.

- Read fills. Fills and account state are available per account and are deterministic: the same inputs produce the same results.

## Assumptions you control

- Slippage is a setting you choose.

- Half-spread is a flat amount you choose, applied to every simulated fill.

- Bars carry no bid or ask. Fills are therefore simulated assumptions, not what a broker would have given you.

## Data coverage

Asset classSourceCoverage

EquitiesSIP bars from third-party data providersRoughly the last two years
Listed optionsOPRA historyFrom 2024-01-18
Expired optionsModeled with Black-Scholes on the underlying's real barsFlat implied volatility that you supply

Modeled option fills use a constant volatility assumption and carry no bid/ask spread, so they are optimistic compared with real trading.

## Not supported

- Futures replay is paused while we replace the data source.

- Papyrus is not a broker and places no real orders.

- Papyrus does not estimate how a strategy would perform in live markets.

## Early access

There is no self-serve signup yet. Tell us what you are backtesting.

[Request early access](/request-access)

Papyrus is a simulation tool. Results are hypothetical, are not based on actual trading, and do not predict or represent future results. Hypothetical results have inherent limitations: they do not account for liquidity, spreads, slippage or market impact the way real trading would, and options results from modeled data use a constant volatility assumption. Papyrus does not provide investment, legal or tax advice, does not execute trades or hold customer funds. Market data is provided by third-party sources and may be delayed, incomplete or inaccurate.

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