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Welcome — this lesson shows how to add CFN-Lint to your development workflow so you can validate AWS CloudFormation templates, catch errors early, and follow recommended best practices before deploying stacks. CFN-Lint (a.k.a. cfn-python-lint) analyzes CloudFormation templates (YAML or JSON), detects syntax/semantic issues, and surfaces suggestions directly in your editor when the CLI is installed and accessible.

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Add the VS Code extension

  1. Open the Extensions pane in Visual Studio Code (click the Extensions icon in the Activity Bar or use the three dots → Extensions).
  2. Search for cfn-lint.
  3. Install the extension named “CloudFormation Linter” (vscode-cfn-lint).
This extension integrates with the CFN-Lint CLI and shows problems inline in editors and the Problems pane.
A Visual Studio Code extensions pane showing the "CloudFormation Linter" (vscode-cfn-lint) extension selected. The panel displays the extension icon, author, ratings, version/download badges, and Disable/Uninstall buttons.

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Open a template to see problems

After installing the extension, open a CloudFormation template. Example YAML:
If the extension detects that the CFN-Lint CLI is not installed or not on your PATH, you may see warnings like:
These messages mean the VS Code extension could not invoke the CFN-Lint CLI. The extension acts as a client — it requires the CLI (a Python package) to be installed locally so it can run checks.
CFN-Lint requires Python 3.8 or later. Ensure Python and pip are installed and available on your PATH. After installing the CLI, restart VS Code so the extension can detect cfn-lint.
On Windows, add Python and your Scripts directory (e.g. C:\Users\<you>\AppData\Local\Programs\Python\Python39\Scripts) to your PATH. On macOS/Linux, verify which python3 and which pip3 (or python3 --version) to confirm availability.

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Where to get the CFN-Lint CLI

Official source and documentation: Common installation methods (choose based on your environment): Quick verification after install:

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Tips for seamless integration

  • If VS Code still shows CLI not found after installing, restart VS Code or your terminal so the PATH updates take effect.
  • Use cfn-lint --info to display rule metadata and guidance for resolving issues.
  • Add CFN-Lint to CI pipelines (Docker or pip installation) to enforce template quality in PRs.

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Next steps in this series

  1. Install Python on your platform (Windows, macOS, or Linux) if you haven’t already.
  2. Install the CFN-Lint CLI using the method that fits your environment.
  3. Restart VS Code and open a CloudFormation template — you should now see inline diagnostics from the extension.
  4. In the next lesson, we’ll configure rule sets, customize ignores, and add CFN-Lint checks to CI workflows.

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