- Software and digital services
- HTTP service
412
HTTP 412 Precondition Failed: meaning and next diagnostic branch
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Medium
Quick answer
HTTP 412 Precondition Failed means: One or more request preconditions evaluated as false on the server. It identifies a protocol result, not the failed component. Preserve one request/response pair and discriminate the ETag or modification timestamp sent, the current validator and which actor changed the resource.
Safety first
Stop and check this first
- Do not remove conditional writes or force an overwrite; doing so can silently destroy another user’s change.
Safe checks you can perform
- Freeze one complete failing exchange
- Change one variable and repeat once
- Stop before retries hide the first failure
Leave these tasks to a qualified professional
- Do not attempt this professional task: Trace-led handoff for HTTP 412
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Trace-led handoff for HTTP 412
What they doCorrelate validators, write sequence, actor and idempotency; design the merge/retry path before changing optimistic-concurrency policy.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Freeze one complete failing exchange
Record HTTP 412, timestamp, method, scheme/host/path without secrets, response headers and body, request ID, client, deployment version and every proxy/CDN/gateway hop. Redact credentials and personal data.
Do not remove conditional writes or force an overwrite; doing so can silently destroy another user’s change.
Evidence: IANA HTTP Status Code Registry · RFC 9110 - HTTP Semantics
Change one variable and repeat once
Read the current resource and validator once, compare it with If-Match/If-Unmodified-Since and retry only after the user or workflow resolves the concurrent change.
Do not remove conditional writes or force an overwrite; doing so can silently destroy another user’s change.
Evidence: IANA HTTP Status Code Registry · RFC 9110 - HTTP Semantics
Stop before retries hide the first failure
A stale validator proves concurrency, not server failure. A missing required precondition is a client contract issue designed to prevent lost updates.
Do not remove conditional writes or force an overwrite; doing so can silently destroy another user’s change.
Evidence: IANA HTTP Status Code Registry · RFC 9110 - HTTP Semantics
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Software and digital services
- Brand
- HTTP
- Product type
- HTTP service
Known code variants
- 412 Échec de précondition
- 412 Precondición fallida
- 412 Precondition Failed
- 412 Precondizione non riuscita
- 412 Vorbedingung fehlgeschlagen
- HTTP 412
- HTTP status 412
What it means
Registered meaning: One or more request preconditions evaluated as false on the server. The next decision boundary is the ETag or modification timestamp sent, the current validator and which actor changed the resource. Before changing infrastructure or buying support, require: Correlate validators, write sequence, actor and idempotency; design the merge/retry path before changing optimistic-concurrency policy.
Warnings and stop conditions
- Lowsource verified
Do not remove conditional writes or force an overwrite; doing so can silently destroy another user’s change.
Evidence: IANA HTTP Status Code Registry · RFC 9110 - HTTP Semantics
Symptoms and causes
Probable causes · in order
- What the registered HTTP status establishesConfirmed
IANA registers 412 as Precondition Failed. The controlling specification establishes: One or more request preconditions evaluated as false on the server.
Evidence: IANA HTTP Status Code Registry · RFC 9110 - HTTP Semantics
- The evidence that changes the next branchPossible
Capture the ETag or modification timestamp sent, the current validator and which actor changed the resource. A stale validator proves concurrency, not server failure. A missing required precondition is a client contract issue designed to prevent lost updates.
Evidence: IANA HTTP Status Code Registry · RFC 9110 - HTTP Semantics
Virtual technician
Does 412 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
IANA HTTP Status Code Registry
Internet Assigned Numbers Authority · 2025 · standard
- 2
IETF / RFC Editor · 2022 · standard
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