---
type: post-synth-check
title: EXT001
description: Extension constraint violation — cross-property validation from cfn-lint extension schemas
id: EXT001
severity: error
category: post-synth
lexicon: aws
docs: https://intentius.io/chant/lexicons/aws/rules/
---
Extension constraint violation — cross-property validation from cfn-lint extension schemas

## Applies to

- [Extension](/types/Extension.md)
- [Map](/types/Map.md)
- [Type](/types/Type.md)