YAML Validator & Linter
About YAML Validator / Linter
YAML Validator / Linter checks YAML streams against YAML 1.2 rules and adds practical warnings for values that are often interpreted differently by older parsers or downstream tools.
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 include a 1-based line and column whenever the parser can locate them.
Implicit-scalar warnings
The linter calls out YAML 1.1 boolean words such as yes and on, leading-zero numbers, timestamp-like strings and implicit null values so you can quote intent explicitly.
Alias safety
Valid documents are resolved with a bounded alias expansion count, surfacing excessively recursive or amplified alias structures as validation errors.
Frequently asked questions
Why is yes reported as a warning rather than a boolean?
Under YAML 1.2 core rules, yes is a string. YAML 1.1 parsers may treat it as true, so quoting it avoids cross-parser surprises.
Are multiple YAML documents supported?
Yes. Documents separated by --- are validated independently and counted in the report.
Does validation upload configuration files?
No. Parsing and linting are fully client-side.
Sources & last verified
The behaviour of this tool and the claims on this page were checked against the specifications below on . Everything 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Found a wrong result or an outdated claim?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 it will be re-verified.