> For the complete documentation index, see [llms.txt](https://docs.flash.trade/flash-trade/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.flash.trade/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/reference/previews.md).

# Previews

`POST` endpoints that compute numbers without building a transaction. Each returns `{ "err": "…" }` in the body when the computation fails. Shared conventions: [Conventions](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/reference/conventions.md). Task walkthrough: [Preview fees & PnL](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/guides/preview-fees-and-pnl.md).

| Method | Path                        |
| ------ | --------------------------- |
| `POST` | `/preview/limit-order-fees` |
| `POST` | `/preview/exit-fee`         |
| `POST` | `/preview/tp-sl`            |
| `POST` | `/preview/margin`           |

***

## Limit-order fees

`POST /preview/limit-order-fees`

Entry price, entry fee, liquidation price, and borrow rate for a would-be position.

| Field            | Type   | Req | Description                                  |
| ---------------- | ------ | --- | -------------------------------------------- |
| `marketSymbol`   | string | ✓   | Market token symbol                          |
| `inputAmountUi`  | string | ✓   | Collateral amount (UI)                       |
| `outputAmountUi` | string | ✓   | Size in target token (UI)                    |
| `side`           | enum   | ✓   | `LONG` / `SHORT`                             |
| `limitPrice`     | string | —   | Limit price (UI); uses live price if omitted |

**Response:** `{ entryPriceUi, entryFeeUsdUi, liquidationPriceUi, borrowRateUi }`.

***

## Exit fee

`POST /preview/exit-fee`

Exit fee and exit price for closing (part of) a position.

| Field              | Type   | Req | Description         |
| ------------------ | ------ | --- | ------------------- |
| `marketSymbol`     | string | ✓   | Market token symbol |
| `side`             | enum   | ✓   | `LONG` / `SHORT`    |
| `closeAmountUsdUi` | string | ✓   | USD to close (UI)   |
| `owner`            | string | ✓   | Owner wallet pubkey |

**Response:** `{ exitFeeUsdUi, exitFeeAmountUi, exitPriceUi }`.

***

## TP/SL

`POST /preview/tp-sl`

`mode` selects the computation: `forward` (trigger price → PnL), `reverse_pnl` (target PnL → trigger price), `reverse_roi` (target ROI% → trigger price).

Supply `owner` to use the caller's existing position; omit it and pass the inline fields to preview before a position exists.

| Field              | Type   | Req | Description                               |
| ------------------ | ------ | --- | ----------------------------------------- |
| `mode`             | string | ✓   | `forward` / `reverse_pnl` / `reverse_roi` |
| `marketSymbol`     | string | ✓   | Market token symbol                       |
| `side`             | enum   | ✓   | `LONG` / `SHORT`                          |
| `owner`            | string | —   | Owner pubkey (owner-position mode)        |
| `entryPriceUi`     | string | —   | Entry price (inline mode)                 |
| `sizeUsdUi`        | string | —   | Position size, USD (inline mode)          |
| `collateralUsdUi`  | string | —   | Collateral, USD (inline mode)             |
| `triggerPriceUi`   | string | —   | Forward: trigger price to price PnL for   |
| `targetPnlUsdUi`   | string | —   | Reverse-PnL: target PnL, USD              |
| `targetRoiPercent` | number | —   | Reverse-ROI: target ROI %                 |

**Response:** `{ pnlUsdUi?, pnlPercentage?, triggerPriceUi?, maxProfitPriceUi? }` — forward returns `pnlUsdUi`/`pnlPercentage`; reverse modes return `triggerPriceUi`.

***

## Margin

`POST /preview/margin`

Preview a collateral add/remove on an existing position.

| Field              | Type   | Req | Description            |
| ------------------ | ------ | --- | ---------------------- |
| `marketSymbol`     | string | ✓   | Market token symbol    |
| `side`             | enum   | ✓   | `LONG` / `SHORT`       |
| `marginDeltaUsdUi` | string | ✓   | Margin delta, USD (UI) |
| `action`           | enum   | ✓   | `ADD` / `REMOVE`       |
| `owner`            | string | ✓   | Owner wallet pubkey    |

**Response:** `{ newLeverageUi, newLiquidationPriceUi, maxAmountUsdUi, existingCollateralUsdUi?, newCollateralUsdUi?, existingLeverageUi?, existingLiquidationPriceUi?, deltaUsdUi? }`.


---

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