Validate templates with cfn-lint

The CloudFormation Linter (cfn-lint) checks JSON and YAML templates against the CloudFormation resource provider schemas and additional rules. It can find invalid resource properties, unsupported values, and common problems before you send a template to CloudFormation.

Source code, release notes, settings, and the complete rule list are available in the cfn-lint repository on GitHub.

Install cfn-lint

Install cfn-lint from Python Package Index (PyPI):

python3 -m pip install cfn-lint

On macOS, you can instead install it with Homebrew:

brew install cfn-lint

For supported Python versions and other installation methods, see the installation instructions on GitHub.

Run cfn-lint

Pass one or more template paths to the command:

cfn-lint template.yaml
cfn-lint template-one.yaml template-two.json

To check templates for more than one AWS Region, use the --regions option:

cfn-lint --regions us-east-1 us-west-2 -- template.yaml

The command returns a nonzero exit code when it finds issues. You can use this behavior to stop an automated build when a template doesn't pass your selected checks.

Configure checks

Use a .cfnlintrc, .cfnlintrc.yaml, or .cfnlintrc.yml file to keep project settings with your templates. You can use this file to select templates, include or ignore checks, choose AWS Regions, and configure rule behavior. For all settings, see Config file in the project documentation on GitHub.

Add cfn-lint to your workflow

You can run cfn-lint from supported editors, automatically before a Git commit, or as part of an automated build. The CloudFormation Language Server also uses cfn-lint to show problems while you type. For Language Server setup, see CloudFormation Language Server.

For editor plugins, GitHub Actions, pre-commit configuration, custom rules, and more examples, see the cfn-lint project documentation on GitHub.