4124xx Client ErrorMedium

HTTP 412 Precondition Failed

Defined in RFC 7232

What Does HTTP 412 Mean?

One or more conditions in the request header fields evaluated to false when tested on the server.

Common Causes

1ETag mismatch in If-Match header
2Resource modified since If-Unmodified-Since date
3Conditional update failed due to stale data
4Optimistic locking conflict

Impact

⚠Update or delete operation is rejected
⚠Need to refresh data and retry

Developer Fix

For web developers and application engineers

1Re-fetch the resource to get the current ETag
2Implement proper optimistic concurrency handling
3Show the user the updated data before retrying

Server Admin Fix

For system administrators and DevOps engineers

1Ensure ETags are generated correctly and consistently
2Monitor for frequent precondition failures
3Verify conditional header processing logic

Frequently Asked Questions

What preconditions can cause a 412?

Headers like If-Match, If-Unmodified-Since, If-None-Match, and If-Modified-Since set preconditions. If the server evaluates them as false, it returns 412 instead of processing the request.

How is 412 different from 409?

412 specifically means a conditional header check failed. 409 is a more general conflict with the resource state. 412 is typically used in ETag-based optimistic locking scenarios.

Related HTTP Status Codes

304Not Modified 409Conflict 428Precondition Required

About the Author

Web Infrastructure Team

Verified against official RFC specifications and real-world server configurations. HTTP status code behavior confirmed across Apache, Nginx, and Cloudflare.