All HTTP status codes

HTTP 428 Precondition Required

Client Error

The server requires the request to be conditional — send If-Match/If-Unmodified-Since to avoid lost-update races.

Defined in RFC 6585

Common causes

  • APIs enforcing optimistic concurrency on writes

How to fix it

  1. GET the resource, capture its ETag, and resend with If-Match

Related status codes

412 Precondition Failed

A conditional header (If-Match, If-Unmodified-Since…) evaluated to false — the resource changed since the client last saw it.

409 Conflict

The request conflicts with the resource's current state — classic cases are duplicate creation and stale optimistic-locking versions.

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