01
Confirm the input format
Auto mode detects a leading JSON object; choose JSON or YAML explicitly if the source is ambiguous. A mismatched forced format gives a parse error instead of silently switching.
Cloud tools
CloudFormation template validator— inspect before you deploy
Paste one JSON or YAML template; inspect local findings and a same-format preview.
CloudFormation template validator
Template input
Diagnostics and preview
No diagnostics in the covered checks.
Processed in this browser; no AWS request is sent.
Enter a template or load an example.
Input limit: 300000 characters.
A CloudFormation template validator helps when a template parses cleanly but a stack still fails on a missing Ref, a misplaced section or a property with the wrong basic type.
Here the source stays editable while diagnostics identify what the local checks actually cover. Use cfn-lint or AWS validation for service behavior and properties outside the bundled snapshot.
Why use this CloudFormation template validator?
Separate syntax from references
A readable YAML file can still refer to an undeclared parameter. This CloudFormation template validator reports parsing and Ref findings separately, with a source position, so you can fix the right layer first.
See where schema coverage stops
Three named resource types receive first-level property checks. Unknown types and dynamic values remain visible as uncovered work rather than a misleading all-clear from the CloudFormation template validator.
Read the scope before exporting
02
Inspect the version and coverage
The absent version means 2010-09-09. The result counts checked S3, SQS and SNS resources separately from unknown types; a warning is a review task, not proof that AWS will reject a resource.
03
Export the current revision
Changing indentation or source makes previous findings stale. Copy the JSON report for review, or download the same-format formatted template; neither action rewrites the input.
Checks tied to CloudFormation structure
JSON and YAML parsing
Parse one template and show the first syntax position. YAML short forms such as !Ref and !Sub remain in the formatted preview; formatting does not convert the template to another language.
Local name resolution
Resolve Ref, Fn::GetAtt and simple Fn::Sub names against declared parameters, resources and AWS pseudo parameters. Missing local names become diagnostics; imported values are not fetched.
A bounded resource snapshot
Check first-level property names and simple types on AWS::S3::Bucket, AWS::SQS::Queue and AWS::SNS::Topic. Intrinsic expressions and nested values are reported as outside this static type check.
What the local result can and cannot establish
- A single template only
- Paste one JSON document or one YAML document. A missing Resources map, invalid logical ID or unsupported format version is reported; nested stacks are not followed.
- The schema is deliberately limited
- Unknown resource types and first-level properties produce coverage warnings. Passing this CloudFormation template validator does not mean all AWS resource specifications were checked.
- Dynamic values remain unresolved
- Ref and Fn functions may depend on parameters, conditions or the account at deployment time. The checker identifies known local names but does not evaluate those values.
- No AWS execution
- No credentials, Region query, stack creation or cloud change occurs. Run AWS validation and your deployment review for permissions, quotas and actual service behavior.
CloudFormation template validator questions
How do I resolve template validation or template format errors in CloudFormation?
Start with the reported syntax line, then inspect section and reference findings. The local report separates JSON/YAML parsing from CloudFormation structure; AWS validation remains the final check.
Why does CloudFormation say YAML not well-formed?
The YAML parser could not build a document. Check indentation, colons and short tags at the shown line. A failed parse produces no formatted export.
What causes unresolved resource dependencies in a CloudFormation template?
A Ref, GetAtt or Sub name has no matching parameter or resource in this single template. Define it or correct the spelling; cross-stack imports are not resolved here.
Why is a template property invalid?
The property may sit outside Resources or be absent from the bundled first-level snapshot. Review the exact path against AWS documentation rather than treating every coverage warning as invalid.
Does validate-template check resource properties?
No. AWS validate-template and deployment can apply additional account, Region and service rules. This CloudFormation template validator reports only its documented local checks.
Still have a question?
Use the CloudFormation template validator now
Recheck after each edit, then carry the current diagnostics into your deployment review.