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

# preflight_failed

> A documented platform constraint failed before we touched the upstream API. The rule field carries the canonical rule id.

The request was syntactically valid but failed a platform-specific rule we check locally before the upstream call. This is the canonical "we caught it before the platform did" error.

## What triggers it

Anything in the [preflight rule catalog](/preflight). A few high-frequency examples:

* Bluesky post text > 300 graphemes ([`bluesky.text.max_graphemes`](/preflight/bluesky-text-max_graphemes))
* Instagram post with no media ([`instagram.media.required`](/preflight/instagram-media-required))
* Instagram media URL not publicly fetchable ([`instagram.media.reachable`](/preflight/instagram-media-reachable) — the canonical `OAuthException 2207052` translator)
* Pinterest pin without a board id and no default board on the connected account ([`pinterest.board.required`](/preflight/pinterest-board-required))

## Response shape

```json preflight_failed.json theme={"system"}
{
  "error": {
    "code": "preflight_failed",
    "message": "Post text is 312 graphemes; Bluesky allows at most 300.",
    "rule": "bluesky.text.max_graphemes",
    "platform": "bluesky",
    "remediation": "Shorten the post to 300 graphemes or fewer.",
    "docUrl": "https://docs.letmepost.dev/errors/preflight_failed",
    "ruleUrl": "https://docs.letmepost.dev/preflight/bluesky-text-max_graphemes",
    "requestId": "req_..."
  }
}
```

`rule` is always set on `preflight_failed`. The `ruleUrl` is the absolute link to that rule's docs page — same path as `/docs/preflight/<rule-with-dashes>/` — so a CLI can `open` it directly without parsing.

## Why preflight matters

Without preflight you'd see this same constraint failure as an opaque platform response — a generic IG `code 100`, a LinkedIn 422 with no field path, a Threads HTTP 200 carrying a status code in the body. Preflight surfaces the rule id directly, with a remediation, before the upstream call ever happens.

## Remediation

Open the rule's page and follow the remediation. Every preflight rule has one.

## Related

* [Preflight](/preflight) — the full rule catalog.
* [`platform_rejected`](/errors/platform_rejected) — preflight passed but the platform still rejected. We treat this as a preflight gap and add a rule.