# Preview Order

Check whether an order is currently admissible without creating an order, reserving funds, or presenting an execution quote.

`OrdersService.PreviewOrder` is an authenticated, account-aware admission preflight. It evaluates a complete order intent without submitting it.

## What Preview checks

Preview evaluates the current inputs used for create admission:

- request validation and execution compatibility
- Pair policy and trading constraints
- fee and risk rules
- available account balance

It creates no order, hold, reservation, or client-order-ID claim.

> **Preview is advisory**
>
> Preview does not walk order-book depth, simulate fills, reserve funds, or guarantee execution. Account state, prices, fees, and Pair policy can change before submission. `CreateOrder` always evaluates the intent again.

## Request shape

`PreviewOrderRequest` and `CreateOrderRequest` both contain:

- optional `subaccount_id`
- required `order: OrderIntent`

Reuse the same `OrderIntent` builder for both operations. Do not maintain a separate flat Preview model. The intent includes symbol, side, sizing, execution, fee asset, client order ID, self-trade prevention, and optional attached risk.

See [Order Sizing](https://testnet.polyester.com/docs/developer-docs/shared-concepts/order-sizing) and [Fee Assets](https://testnet.polyester.com/docs/developer-docs/shared-concepts/fee-assets) for those independent choices.

## Request examples

## REST JSON

Send the nested order object to `POST /v1/orders/preview`:

```json
{
	"order": {
		"symbol": "BTC-USDT",
		"side": "BUY",
		"baseQty": "0.001",
		"feeAsset": "QUOTE",
		"limitGtc": {
			"price": "50000.00",
			"postOnly": true
		}
	}
}
```

## ConnectRPC ProtoJSON

Call `/orders.v1.OrdersService/PreviewOrder`:

```json
{
	"order": {
		"symbol": "BTC-USDT",
		"side": "BUY",
		"baseQtyScaled": "100000",
		"feeAsset": "QUOTE",
		"limitGtc": {
			"priceTicks": "50000000000",
			"postOnly": true
		}
	}
}
```

The examples assume the Pair scales have already been applied. See [Scaled Integers](https://testnet.polyester.com/docs/developer-docs/connectrpc/scaled-integers).

## Response fields

| Protobuf field                | Meaning                                                                       |
| ----------------------------- | ----------------------------------------------------------------------------- |
| `admissible`                  | Whether current admission and available-balance checks passed                 |
| `rejection`                   | Typed `ErrorDetail` when the order is not currently admissible                |
| `resolved_base_qty_scaled`    | Gross base quantity resolved during admission, when sizing reached resolution |
| `protected_price_bound_ticks` | Protective execution boundary, when price protection reached resolution       |
| `evaluated_at`                | Time at which the admission evaluation completed                              |

REST exposes the optional resolved values as `resolvedBaseQty` and `protectedPriceBound`.

`protected_price_bound_ticks` is a safety boundary, not an expected fill price. Preview does not return expected fills, order-book depth, quote debit, fees, net proceeds, or required balance. Reservation and fee-ceiling calculations remain internal to the admission check.

## Rejections and transport errors

Insufficient funds is a completed preview result. `admissible` is false and `rejection.code` is `ERROR_CODE_INSUFFICIENT_FUNDS`.

Authentication failures, malformed requests, and failures that prevent evaluation still use normal RPC or HTTP errors. Preserve `ErrorDetail.code` and every field violation rather than parsing human-readable messages.

## Interface availability

Preview is available through REST and ConnectRPC. The SBE WebSocket command path does not expose a Preview command.