DynamoDB ValidationException

TL;DR — A ValidationException means DynamoDB rejected the request as malformed before touching any data. Read the message text: it names the exact parameter at fault. Nothing was written, so fix the request shape and retry.

What it means

ValidationException is DynamoDB's catch-all client error (HTTP 400) for a request that fails validation — a bad expression, a value in the wrong type wrapper, a key that doesn't match the table's schema, or a limit exceeded. It is not retryable: sending the same request again produces the same error.

Because it is a family of errors, the fix depends entirely on the message string. The most common variants each have their own page:

• Query condition missed key schema element
• The provided key element does not match the schema
• Invalid UpdateExpression syntax
• ExpressionAttributeValues contains invalid value
• Item size has exceeded the maximum allowed size

Why it happens

• A KeyConditionExpression that doesn't include the partition key, or references a non-key attribute.
• A key attribute whose type doesn't match the table definition (e.g. sending a number as a string).
• A malformed UpdateExpression / ConditionExpression / FilterExpression — a reserved word used raw, a missing #name or :value placeholder.
• Empty values where they aren't allowed, or an attribute that resolves to an unsupported type.
• A limit exceeded — item over 400 KB, too many items in a BatchWriteItem, expression too long.

How to fix it

1. Read the full message. DynamoDB tells you which parameter failed — the string is precise ("Invalid UpdateExpression: Attribute name is a reserved keyword; reserved keyword: status").
2. Match it to the variant above and apply that page's fix.
3. Validate the request shape locally before sending — most ValidationExceptions are a typo in an expression or a type wrapper.

FAQ

Is a DynamoDB ValidationException retryable? No. The request itself is malformed, so sending it again produces the same error. Read the message text — it names the exact parameter at fault — fix the request shape, and then retry.

What are the most common causes of a ValidationException? A KeyConditionExpression that omits the partition key or references a non-key attribute, a key attribute whose type doesn't match the table definition, a malformed expression using a reserved word or a missing placeholder, empty values where they aren't allowed, or a limit exceeded such as an item over 400 KB.

Related errors

• ConditionalCheckFailedException — a condition failed (not malformed; the write was valid but rejected).
• ResourceNotFoundException — the table or index doesn't exist.
• Learn: Expression names & values · Update expressions

References

• Error handling with DynamoDB — Amazon DynamoDB Developer Guide
• Constraints in Amazon DynamoDB — Amazon DynamoDB Developer Guide
• Reserved words in DynamoDB — Amazon DynamoDB Developer Guide

Last verified 2026-07-13 against the official AWS documentation linked above.