- Software and digital services
- HTTP service
428
HTTP 428 Precondition Required: meaning and next diagnostic branch
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Medium
Quick answer
HTTP 428 Precondition Required means: The origin requires the request to be conditional to prevent a lost-update conflict. 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 428
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 428
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 428, 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 6585 - Additional HTTP Status Codes
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 6585 - Additional HTTP Status Codes
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 6585 - Additional HTTP Status Codes
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
- 428 Precondición requerida
- 428 Precondition Required
- 428 Précondition requise
- 428 Precondizione richiesta
- 428 Vorbedingung erforderlich
- HTTP 428
- HTTP status 428
What it means
Registered meaning: The origin requires the request to be conditional to prevent a lost-update conflict. 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 6585 - Additional HTTP Status Codes
Symptoms and causes
Probable causes · in order
- What the registered HTTP status establishesConfirmed
IANA registers 428 as Precondition Required. The controlling specification establishes: The origin requires the request to be conditional to prevent a lost-update conflict.
Evidence: IANA HTTP Status Code Registry · RFC 6585 - Additional HTTP Status Codes
- 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 6585 - Additional HTTP Status Codes
Virtual technician
Does 428 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
RFC 6585 - Additional HTTP Status Codes
IETF / RFC Editor · 2012 · standard
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