YAML validator and linter
About YAML Validator / Linter
The YAML validator and linter checks YAML files against YAML 1.2 rules. It also warns about values that older parsers or other tools may read differently.
How it works
Strict YAML 1.2 parsing
Every document is parsed with the YAML 1.2 core schema, strict syntax checks and unique mapping keys. Errors show a 1-based line and column when the parser can find them.
Ambiguous value warnings
The linter flags YAML 1.1 boolean words such as yes and on, numbers with leading zeros, strings that look like timestamps and implicit nulls. Quote them to make your intent clear.
Alias safety
Valid documents are resolved with a cap on alias expansions. Alias structures that grow too large or recurse are reported as errors.
Frequently asked questions
Why is yes reported as a warning rather than a boolean?
In YAML 1.2 core, yes is a string. YAML 1.1 parsers may read it as true, so quoting it avoids surprises.
Are multiple YAML documents supported?
Yes. Documents separated by --- are validated one by one and counted in the report.
Are my config files uploaded?
No. Parsing and linting run in your browser.
Sources & last verified
We checked this tool's behavior and the claims on this page against the specifications below on . The tool runs in your browser, so the output you see is exactly what the engine produced.
Found a wrong result or an outdated claim? Report an error and we will check it again.
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