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Idempotency keys for POST: safe retries without duplicate side effects
Clients replay requests on flaky networks; idempotency keys let servers collapse duplicates deterministically.
1 min read
restreliabilityapi-design
Interaction with CORS
Custom Idempotency-Key headers usually trigger preflight—ensure OPTIONS allows them alongside POST.
Expose whether a retry was deduplicated via a response header for observability in clients.
Design checklist
Scope keys per API key or user to prevent cross-tenant collisions.
Return the same status and body for duplicate submissions within the idempotency window.