HTTP 412 Precondition Failed — What It Means & How to Fix It

The HTTP 412 Precondition Failed status code indicates one or more conditions specified in the request headers evaluated to false on the server. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: This occurs when conditional headers like If-Match or If-Unmodified-Since fail their checks.. It is used in optimistic concurrency control to prevent lost updates.. The client should fetch the latest version and retry with updated preconditions.. Common in APIs that use ETags for conflict detection.. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: The If-Match header contains an ETag that no longer matches the current resource.. The If-Unmodified-Since date is older than the resource last modification time.. Another client modified the resource between your GET and PUT/PATCH.. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Fetch the latest version of the resource to get the current ETag.. Merge your changes with the latest version.. Retry the request with the updated ETag in the If-Match header.. Implement retry logic for concurrent modification scenarios.. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our HTTP Status Codes collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.