CloudFormation Validator

What this tool does

Paste a CloudFormation template — YAML or JSON — and it's checked against the documented template structure: required sections, resource shape, and whether every Ref and Fn::GetAtt in the template actually points at something that exists. YAML shorthand intrinsic functions (!Ref, !GetAtt, !Sub, !If, and the rest) are understood and resolved to their full Fn:: form before checking.

What this tool is not

This is structural validation, not deployment validation. It can't tell you whether a resource's Properties are actually valid for that specific resource type — each of the hundreds of AWS resource types has its own property schema, and checking those requires the type-by-type resource and property types reference that real deployment does. For that level of checking, use aws cloudformation validate-template or cfn-lint. This tool catches the mistakes that happen before any of that — a typo'd section name, a missing Type, a Ref to a resource that doesn't exist — entirely in your browser, with no AWS credentials involved.

What gets checked

• Top-level sections — only Resources is required; anything outside the ten documented section names is flagged.
• AWSTemplateFormatVersion — the only valid value is "2010-09-09".
• Each resource — a Type matching AWS::Service::ResourceType (or Custom::Name), logical IDs that are alphanumeric-only, and no attributes outside the documented set (Type, Properties, DependsOn, Condition, Metadata, DeletionPolicy, UpdateReplacePolicy, CreationPolicy, UpdatePolicy).
• Dangling references — every Ref and Fn::GetAtt target is checked against the template's own resources, parameters, and the eight AWS pseudo parameters (AWS::AccountId, AWS::Region, and so on).

FAQ

Why does a valid-looking Ref show a warning?

Most likely a typo in a resource's logical ID, or the resource genuinely doesn't exist in this template yet — a very common copy-paste mistake when assembling a template from multiple snippets.

Can this check an IAM policy embedded in a template?

Not automatically — pull the policy document out and paste it into IAM Policy Viewer for a statement-by-statement breakdown.

Is my template sent anywhere?

No — parsing and validation happen entirely in your browser. Nothing you paste here is ever sent to a server.

How does CloudFormation compare to Terraform?

See CloudFormation vs Terraform for the concrete differences — state management, change previews, failure handling, and licensing — rather than just "which is more popular."