# Preview a timezone-aware publishing cadence

> Markdown version of https://docs.postlake.dev/api/post-posts-cadence-preview . The canonical page for humans.
> PostLake is the social media API for AI agents: https://postlake.dev/llms.txt

`POST /v1/posts/cadence/preview`

Returns deterministic UTC slots without creating, reserving, or charging for posts. Call POST /v1/posts/validate for each proposed post before creating it. Platform pacing limits remain authoritative at publish time. Ambiguous or nonexistent local times are rejected.

## Request

Authenticate with a bearer API key. Agents calling over MCP authorise with OAuth instead and never handle the key.

```bash
curl -X POST https://api.postlake.dev/v1/posts/cadence/preview \
  -H "Authorization: Bearer $POSTLAKE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"timezone":"Europe/London","startDate":"2026-10-01","days":7,"localTime":"09:00","tracks":[{"id":"main"},{"id":"shorts","staggerMinutes":45}]}'
```

### Body

| Field | Type | Required | What it is |
| --- | --- | --- | --- |
| `timezone` | string | Yes | IANA timezone, such as Europe/London. |
| `startDate` | string | Yes |  |
| `days` | integer | Yes |  |
| `localTime` | string | Yes | Local HH:mm start time. |
| `tracks` | array of object | Yes |  |
| `gapMinutes` | integer | No |  |
| `occupiedAt` | array of string | No | Existing UTC or offset-qualified posts to avoid. No database lookup is performed. |


## Response

Read-only slot preview (`200`).

| Field | Type | Required | What it is |
| --- | --- | --- | --- |
| `timezone` | string | Yes |  |
| `slots` | array of object | Yes |  |



### Example

```json
{
  "timezone": "…",
  "slots": [
    {
      "date": "…",
      "track": "…",
      "localTime": "…",
      "scheduledAt": "…"
    }
  ]
}
```


## Calling this from an agent

Agents do not call REST. They call tools. Over the hosted MCP server this operation is `preview_cadence`, and the agent authorises with OAuth so your API key is never pasted into a chat or seen by the model. You control what any one agent may do: which brands it may act for, which networks it may reach, how much a day, and whether it may spend credits bought up front.

## Errors

Every failure uses one shape: a stable `type`, a granular `code`, the field at fault in `param`, and a plain-language `fix`. See https://docs.postlake.dev/errors.md .

Check the result before retrying a write. Only operations that explicitly support idempotency can safely replay an `Idempotency-Key`.

## Common questions

**Can an AI agent do this without the REST API?**

Yes. Over MCP the same job is the preview_cadence tool. The agent authorises with OAuth, so no API key is pasted into a chat or seen by the model, and the answer comes back in the same normalised shape.

**Is it safe to retry this call?**

Yes. This preview is read-only. It creates no posts, reserves no slots, and spends no credits. Send the same input again to get the same slots while the intended start time remains in the future.

**What happens when it fails?**

You get one error shape: a stable type, a granular code you can branch on, the offending field in param, and a fix written so an agent can correct itself rather than stop. Full list on Errors and retries.

## Related

- [Cancel a scheduled post, discard a draft, or retract a live one](https://docs.postlake.dev/api/delete-posts-by-id.md) `DELETE /v1/posts/{id}`
- [Recover a creation receipt without replaying a write](https://docs.postlake.dev/api/get-idempotency-receipt.md) `GET /v1/idempotency/{key}`
- [List posts](https://docs.postlake.dev/api/get-posts.md) `GET /v1/posts`
- [Get post](https://docs.postlake.dev/api/get-posts-by-id.md) `GET /v1/posts/{id}`