412 Precondition Failed

A precondition in the request headers (If-Match, If-Unmodified-Since, If-None-Match) was false.

412 at a glance

Code: 412
Name: Precondition Failed
Class: 4xx Client error
Status: IANA-registered standard code
Defined in: RFC 9110, Section 15.5.13
Cacheable by default: No by default. Caches store it only when the response carries explicit freshness (Cache-Control max-age, s-maxage or Expires).

What 412 means

412 Precondition Failed means the server evaluated a conditional header on a state-changing request and it did not hold. It is how optimistic concurrency works: "update only if the ETag is still X". If someone else changed the resource first, the update is rejected instead of silently overwriting their change.

What typically causes a 412

If-Match with an outdated ETag on PUT, PATCH or DELETE.
S3 conditional writes: If-None-Match: * on PutObject when the key already exists.
Azure Storage and Cosmos DB ETag checks; Google Cloud Storage ifGenerationMatch.
CouchDB and other document stores rejecting a stale revision.

Fix it on the server

Return the current ETag so the client can re-fetch and retry.

Fix it as a client or visitor

GET the resource again, re-apply your change to the new version, and retry with the new ETag.

Headers that go with 412

Header	Role
`If-Match`	Request precondition on the ETag.
`If-Unmodified-Since`	Date-based precondition.
`ETag`	Current version.

Example response

HTTP/1.1 412 Precondition Failed
ETag: "v42"
Content-Type: application/json

{"error": "Resource was modified (current ETag v42)"}