About the YAML Validator
Most YAML failures are invisible in a text editor: a tab where spaces were expected, a value indented one column too far, a colon inside an unquoted string, a duplicate key. The validator parses the text with a strict YAML 1.2 parser and reports the first problem with its line and column and a plain-language reason such as "bad indentation of a mapping entry" or "duplicated mapping key".
When the document is valid, the result lists each document in the file (multi-document files are common in Kubernetes) and whether it is a mapping, a sequence or a scalar, with the number of top-level keys or items. That is enough to confirm that a template rendered the structure you intended.
This checks syntax and the core data model, not the schema of a particular tool. A valid YAML file can still be an invalid Kubernetes manifest or GitHub workflow; those checks belong to the tool that consumes the file. After validating, the YAML Formatter normalises the indentation so the mistake cannot recur.
How to use
- Paste the YAML.
- Read the result: a document summary, or the error line and column.
- Go to that line in the left pane, fix it, and watch the result update.
Common questions
- Are tabs allowed in YAML?
- Not for indentation. The validator reports a tab as an error at the exact position; replace it with spaces.
- Why is "key: value: other" an error?
- A colon followed by a space inside an unquoted value starts a new mapping. Quote the value.
- Does it accept multiple documents?
- Yes. Documents separated by --- are validated individually and listed in the result.
- Are duplicate keys reported?
- Yes. YAML 1.2 forbids them and the validator names the key.