HTTP 428 Precondition Required — Conditional Headers Mandatory

Overview

HTTP 428 Precondition Required means the server requires the request to include conditional headers like If-Match to prevent lost update problems.

Key Details

• Server mandates conditional headers (If-Match, If-Unmodified-Since) for this request
• Prevents the lost update problem where concurrent changes overwrite each other
• The server is enforcing optimistic concurrency control
• You must first GET the resource to obtain the current ETag, then use If-Match
• Different from 412 where conditions were sent but failed — 428 means conditions were not sent at all

Common Causes

• API requires If-Match header but client did not include it
• PUT or PATCH request without conditional headers on a protected resource
• Server enforcing optimistic locking on all write operations
• Version-controlled resource requiring version check before modification

Steps

1. 1First make a GET request to obtain the resource's current ETag
2. 2Include If-Match: "etag-value" header in your PUT/PATCH/DELETE request
3. 3If using If-Unmodified-Since, include the Last-Modified date from the GET response
4. 4Update your API client to always fetch before modifying protected resources
5. 5Check API documentation for which endpoints require conditional headers

Tags

More in 4xx Client Error

Frequently Asked Questions