ValidationException
AWS ValidationException (Validation Exception) means the input fails service validation constraints. In AWS APIs, this error returns HTTP 400.
Last reviewed: March 29, 2026|Editorial standard: source-backed technical guidance
What Does Validation Exception Mean?
When ValidationException is returned, AWS rejects the payload at validation gates, so the operation never executes and users see immediate request-level failure until input constraints are fixed.
Common Causes
- -Required fields are missing or provided with unsupported types, lengths, or formats.
- -Operation-specific constraints are violated even though payload shape looks syntactically valid.
- -Nested objects contain invalid enum values, nullability violations, or contradictory settings.
- -Client-side schema assumptions are stale compared with current service API contracts.
How to Fix Validation Exception
- 1Parse the first validation message and correct the named field before broader refactors.
- 2Validate payload against the exact operation schema from the official API reference.
- 3Re-run with minimal known-good input, then add optional fields incrementally.
- 4Upgrade SDK/service models when generated clients lag behind API contract changes.
Step-by-Step Diagnosis for Validation Exception
- 1Capture request ID, raw request payload, and full validation message from the failing call.
- 2Diff failing payload against successful payloads for the same operation and environment.
- 3Validate ranges, regex patterns, enums, and required combinations for every nested field.
- 4Add CI tests for edge, malformed, and boundary cases that previously escaped checks.
Schema and Contract Review
- -Parse the exact operation contract and required nested fields before send (example: DynamoDB rejects requests when key schema attribute types do not match table definition).
- -Inspect generated request shape against current API model versions (example: stale SDK model emits optional blocks now rejected by the service).
Input Constraint Checks
- -Verify ranges, regex patterns, and enum domains for each constrained field (example: region/service-specific enum values accepted in one context can fail in another).
- -Audit cross-field rules and conditional dependencies (example: one flag selection makes another field mandatory and missing values trigger ValidationException).
How to Verify the Fix
- -Replay the exact request path and confirm ValidationException is resolved.
- -Confirm response objects and side effects match expected business behavior.
- -Verify no new validation failures appear in adjacent API workflows.
How to Prevent Recurrence
- -Generate runtime validators from service schemas and enforce them at API boundaries.
- -Block releases when contract tests detect schema drift or invalid default values.
- -Track validation failure trends by operation to catch regressions early.
Pro Tip
- -keep per-operation golden payload fixtures and diff serialized requests against them on every SDK or template change.
Decision Support
Compare Guide
HTTP 400 vs 422: Bad Request vs Unprocessable Content
Fix API payload issues faster by using 400 for malformed syntax and 422 for semantic validation failures, so clients correct format before business rules.
Playbook
CORS Error Fix Playbook (Preflight / Origin / Credentials)
Use this playbook to separate browser-enforced cross-origin policy failures from server-side CORS header and route defects and apply strict origin and credential controls safely.
Playbook
Validation Failure Playbook (400 / 422 / INVALID_ARGUMENT)
Use this playbook to separate malformed-request failures from semantic validation failures, then fix request contracts without broad server-side bypasses.
Official References
Provider Context
This guidance is specific to AWS services. Always validate implementation details against official provider documentation before deploying to production.