YAML Validator
Validate YAML and locate syntax errors with line, column and a code frame — locally in your browser, nothing uploaded.
🔒 Your YAML stays in your browser. Nothing is uploaded.
What does this tool do?
YAML Validator checks whether a YAML document is syntactically valid. If it is, you get a clear confirmation and the number of documents found. If it is not, you get the error with its line and column and a short code frame pointing at the problem — so you can fix it without guessing.
What YAML is validated
This tool validates YAML 1.2 (core schema). That means plain scalars stay
plain: yes, no, on and off are strings, and a value such as
2026-09-10 is a string, not a date. It accepts the usual structure — nested
mappings, sequences, quoted and multiline strings, and numbers.
Indentation: spaces, not tabs
YAML is indentation-sensitive, and tabs are not allowed for indentation. A common source of errors is mixing tabs and spaces, or dedenting a mapping at the wrong column. The validator reports exactly where the indentation breaks.
Anchors, aliases and merge keys
Anchors (&name), aliases (*name) and merge keys (<<: *name) are supported,
so you can validate configurations that reuse blocks. Undefined aliases and
malformed anchors are reported as errors.
Multi-document YAML
A stream separated by --- markers is validated as multiple documents. An error
in any document is reported with the line and column where it occurs.
Duplicate keys
Duplicate mapping keys are treated as invalid. If the same key appears twice, the validator reports it, because relying on “the last one wins” is a frequent source of configuration bugs.
YAML Validator vs Code Formatter
These are different jobs:
- Code Formatter makes YAML look tidy (indentation and spacing).
- YAML Validator tells you whether it is valid and exactly where it breaks.
A file can be invalid but “formatted”, or valid but ugly. Use each for what it does.
Limits
Inputs up to about 500 KB validate instantly. Between 500 KB and 1 MB you will see a warning, and inputs above 1 MB are rejected. YAML parsing is slower than JSON, so this limit keeps the tool responsive in the browser.
Privacy
Your YAML is parsed locally in your browser. It is not uploaded, stored or sent anywhere — safe for secrets in configuration files.