Free Online YAML Validator
Validate YAML syntax with detailed error messages and line numbers. Format YAML with proper indentation.
data_object Input YAML
Characters: 0
Lines: 0
code Output Result
Click Validate to check YAML syntax, or Format to beautify YAML.
Key Features
Instant Validation
Validate YAML syntax using the js-yaml parser -- trusted by ESLint and Webpack.
Error Detection
Get detailed error messages with line numbers for quick debugging of YAML syntax issues.
YAML Formatting
Format YAML with consistent 2-space indentation using js-yaml's dump function.
Privacy Protected
All processing happens locally in your browser. No data ever leaves your device.
Frequently Asked Questions
Getting Started
What is a YAML validator?
The YAML Validator checks whether a YAML document conforms to the YAML specification, using the js-yaml library -- the same parser trusted by ESLint, Webpack, and many Node.js tools. It catches indentation errors, invalid mappings, duplicate keys, and structural problems.
Is this YAML validator free?
Yes. All tools are completely free and run locally in your browser. No signup, no limits, no hidden costs.
Does the tool store my data?
No. Your YAML data never leaves your browser. All processing happens locally on your device, ensuring complete privacy and security.
Features & Usage
Why does YAML require spaces instead of tabs?
The YAML spec explicitly forbids tab characters for indentation because different editors display tabs at different widths (2, 4, or 8 spaces), making it impossible to guarantee consistent structure across environments.
Can this tool validate Kubernetes manifests?
This validator checks YAML syntax, not Kubernetes schema correctness. A manifest can be valid YAML but still fail kubectl apply because it references a nonexistent API version or uses a wrong field name. Use this tool to catch syntax errors first.
What happens if my YAML has duplicate keys?
js-yaml will throw an error if it detects duplicate keys within the same mapping. Duplicate keys are almost always a mistake and the validator forces you to resolve the ambiguity.
Does formatting change the semantics of my YAML?
Formatting uses js-yaml's dump function, which re-serializes the parsed data. The formatted output is semantically equivalent to the input but may differ in style -- comments are stripped, flow-style mappings may be converted to block style, and scalar quoting may change.