YAML Validator
Catches tabs, duplicate keys and colon spacing, with line numbers
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How to use
YAML failures are overwhelmingly structural rather than exotic, and the parser messages they produce are famously unhelpful. This checks for the specific mistakes that cause real CI failures and explains each one.
Paste your YAML
Workflow files, Kubernetes manifests, Docker Compose files or application config. Checking runs as you type.
Fix errors first
Errors will break parsing outright. Tabs in indentation and duplicate keys are the two most common, and both are invisible when reading the file normally.
Review the warnings
Warnings are things that usually indicate a mistake but may parse — most often a missing space after a colon, which turns key:value into a single scalar string rather than a mapping.
Examples
The tab that breaks a pipeline
A single tab character in indentation makes the entire document invalid. It looks identical to spaces in most editors, and the resulting parser error rarely points at the real line — this reports it directly.
A duplicate key that changes behaviour
Defining name twice at the same level is not an error in many parsers — the later value simply wins. In a config file this silently discards the earlier setting, which is reported here as an error.
About this tool
Check YAML for the structural mistakes that actually break pipelines: tabs used for indentation, duplicate keys that silently overwrite each other, unclosed quotes, and missing spaces after colons. Every issue is reported with its line number and an explanation of why it matters.