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

# preview_order

> Preview a 100-coin position before placing it (step 1 of 2)

Computes the summary the user is meant to confirm before taking a position, and
— when the order is currently possible — mints the `confirm_token`
[`place_order`](/mcp/tools/place-order) needs.

**Scope**: `write` · **Annotations**: `readOnlyHint`
**REST equivalent**: `POST /open/v1/topics/{id}/order-preview`

<Note>
  This tool **charges nothing** and does not reserve anything. It counts against
  the read window only, so an agent can freely price a few options before asking.
</Note>

## Parameters

| Name        | Type                                     | Required | Default | Notes                      |
| ----------- | ---------------------------------------- | -------- | ------- | -------------------------- |
| `topic_id`  | string (uuid)                            | ✅        | —       | `v21_lmsr` topics only     |
| `option_id` | string (uuid)                            | ✅        | —       | From the topic's `options` |
| `language`  | see [languages](/mcp/overview#languages) |          | `en`    |                            |

## Returns

Every `v21_lmsr` order is a fixed **100 coins**. `payout_if_correct_rubies` is
what the option pays if it turns out correct — that many **rubies**, with the
100-coin stake *not* returned. `price_after` is where the option's price lands
once this order joins the book.

`avg_price` is coins paid per ruby (`stake / units`). It always sits above
`price_now` and below `price_after`, since the order moves the price up as it
fills. It carries **6 decimal places** — the one field that departs from the
4-decimal convention, because it is a ratio rather than a price.

Captured live:

```json theme={null}
{
  "can_place": true,
  "summary": {
    "topic_title": "Will the Fed cut rates at the November 2026 meeting?",
    "option_label": "Yes",
    "stake_coins": "100.0000",
    "balance_before": "5000.0000",
    "balance_after": "4900.0000",
    "price_now": "0.5000",
    "price_after": "0.5244",
    "payout_if_correct_rubies": "195.2372",
    "avg_price": "0.512197",
    "close_time": "2026-10-06T23:34:02.46058Z",
    "mechanism": "v21_lmsr"
  },
  "confirm_token": "oc1.eyJhIjoicGxhY2Vfb3JkZXIi…YP6hrtHyqIdsOX_s",
  "expires_at": "2026-09-08T23:39:11.993467Z"
}
```

<Warning>
  **Show the summary to the user and get their explicit confirmation before
  calling the execute tool.** The token is what proves a preview happened — it is
  not a substitute for asking.
</Warning>

## When the order can't be placed

`can_place` is `false`, `reason` says why, and **no token is issued**:

| `reason`                | Meaning                                                                          |
| ----------------------- | -------------------------------------------------------------------------------- |
| `TOPIC_CLOSED`          | Past `close_time`, or a ruling has started                                       |
| `ALREADY_STAKED`        | The owner already holds a position — one order per topic, no adding or switching |
| `INSUFFICIENT_BALANCE`  | Fewer than 100 coins                                                             |
| `MECHANISM_UNSUPPORTED` | A legacy `v2_share` topic; this surface only trades `v21_lmsr`                   |

The summary is still returned so the agent can explain the situation with real
numbers:

```json theme={null}
{
  "can_place": false,
  "reason": "ALREADY_STAKED",
  "summary": {
    "topic_title": "Will the Fed cut rates at the November 2026 meeting?",
    "option_label": "Yes",
    "stake_coins": "100.0000",
    "balance_before": "4899.0000",
    "balance_after": "4899.0000",
    "price_now": "0.4988",
    "price_after": "0.5233",
    "payout_if_correct_rubies": "195.6806",
    "avg_price": "0.511037",
    "close_time": "2026-10-06T23:34:02.46058Z",
    "mechanism": "v21_lmsr"
  }
}
```

<Note>
  With `MECHANISM_UNSUPPORTED` the summary is partial — only `topic_title`,
  `option_label`, `stake_coins`, the balances, `price_now`, `close_time` and
  `mechanism` are meaningful.
</Note>

## Example prompts

* "What would it cost me to back Yes on the Fed market?"
* "If I'm right on this one, what do I get?"

## Related

[`place_order`](/mcp/tools/place-order) ·
[`get_topic`](/mcp/tools/get-topic) ·
[`list_my_positions`](/mcp/tools/list-my-positions)