A template can fail at four stages: as YAML, against the resource schemas, against your organization's rules, and only when AWS 24 actually deploys it. Each stage has its tool, and the cheap ones should run first, on every commit: cfn-lint 2,641 for schemas and correctness, cfn-guard 1,388 for policy, and a real deployment, on LocalStack 63,725 here or in throwaway AWS regions with TaskCat 1,204 , for the rest.
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Linting and Testing
Linting, Policy Checks and Template Testing