YAML Validator

YAML Validator

YAML validator online free. Validate YAML syntax with line and column error reporting. Clear error messages—validate YAML files instantly.

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YAML Input

YAML Syntax Tips

key: value — Basic pair
- item — List item
"string" — Quoted string
# comment — Comment

Features

  • Validate YAML syntax with detailed error messages and line numbers
  • Parse and display the resulting data structure as a tree
  • Detect common issues: unclosed quotes, bad indentation, duplicate keys
  • Support for multi-document YAML (--- separator)
  • Character-level error highlighting
  • Schema validation for popular formats (Kubernetes, GitHub Actions, Docker Compose)

Common Use Cases

  • Verify a configuration file before deploying an application
  • Debug parse errors from CI/CD runners or deployment tools
  • Validate programmatically generated YAML output
  • Check Kubernetes manifests before applying with kubectl
  • Verify Helm values files and chart templates

YAML Validation

Validation ensures your YAML is syntactically correct — that it can be parsed into a data structure without errors. A valid YAML file has correct indentation, properly balanced quotes, no illegal characters in unquoted strings, and valid key-value pairs.

Validation is the minimum bar: even perfectly valid YAML can have logical errors (wrong key names, missing required fields). For those, you need schema validation, which checks the parsed structure against a defined schema (like JSON Schema or CRD specs for Kubernetes).

Examples

Valid - Valid YAML
name: my-app
version: 1.2.3
enabled: true
tags:
  - web
  - api
Invalid - Invalid (wrong indent)
name: my-app
  version: 1.2.3
Invalid - Invalid (unclosed quote)
message: "Hello World

Frequently Asked Questions

What makes a YAML file invalid?

Common causes of YAML parse errors:

  • Inconsistent indentation or mixing tabs/spaces
  • Unclosed quotes (single or double)
  • Special characters (:, #, {, }) in unquoted strings
  • Colons without a space after them inside mappings
  • Multi-line strings that break the indentation context

Is valid YAML always safe to use?

No. A YAML file can parse successfully but still be semantically wrong — referencing keys that don't exist, using wrong types (string instead of number), or missing required fields. For critical configs, also validate against a schema specific to your tool (e.g., Kubernetes API schemas, OpenAPI specs).

How do I validate YAML in a terminal?

Use python3 -c "import yaml, sys; yaml.safe_load(sys.stdin)" as a quick check. For more advanced output, install yamllint via pip: pip install yamllint && yamllint myfile.yaml.

What does "expected block end" mean?

This typically means the parser expected to close a mapping or sequence block but found something unexpected — usually caused by a bad indent on the next key. Indent the problematic line correctly to resolve it.

Related Tools

YAML Linter

Style and best-practice checks

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YAML Formatter

Format and normalize YAML

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JSON Validator

Validate JSON documents

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K8s Inspector

Inspect Kubernetes manifests

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💡 Tips

  • Always validate YAML in your editor with a plugin (e.g., YAML by Red Hat in VS Code) for instant feedback.
  • If a file parses on your machine but not in production, check if the production parser uses a different YAML version (1.1 vs 1.2).
  • Use <code>yaml.safe_load()</code> instead of <code>yaml.load()</code> in Python — the latter allows arbitrary code execution via YAML anchors.
  • Multi-document YAML (using <code>---</code>) is useful for Kubernetes but can confuse tools expecting single-document files.