YAML Validator

Paste or type YAML to instantly validate, format, and detect errors with line numbers.

Keys may be reordered in the formatted output — this is normal behaviour of the YAML serializer and does not affect validity.

Common YAML Mistakes

  • × Tabs instead of spaces — YAML requires spaces for indentation, never tabs.
  • × Inconsistent indentation — nested items must align exactly.
  • × Missing space after colon — key:value is invalid; use key: value.
  • × Unquoted special characters — strings with : # { } should be quoted.

YAML Tips

  • ✓ Multi-document — separate documents with --- on its own line.
  • ✓ Comments — use # for inline or full-line comments.
  • ✓ Multi-line strings — use | (literal) or > (folded) block scalars.
  • ✓ Anchors & aliases — use &anchor and *alias to reuse values.

Frequently Asked Questions

What is YAML?

YAML (YAML Ain't Markup Language) is a human-readable data serialisation format commonly used for configuration files — Docker Compose, Kubernetes, GitHub Actions, and many more.

Why are my keys reordered in the output?

YAML objects are unordered by spec. The js-yaml serialiser may sort or reorder keys — this doesn't change the meaning of the document and the output is still valid YAML.

Does this support multi-document YAML?

Yes. Separate documents with --- on its own line. Each document is validated and formatted individually.

Is my data sent anywhere?

No — all validation happens entirely in your browser using js-yaml. Nothing is sent to any server.

About YAML Validator

The YAML Validator is a free online tool that checks your YAML syntax instantly, highlights errors with exact line and column numbers, and formats your document for readability — all without leaving your browser.

  • Real-time validation as you type with 300 ms debounce
  • Precise error location — line number and column shown in the editor
  • Formatted output with consistent 2-space indentation
  • Multi-document YAML support using --- separators
  • Context snippet showing the lines surrounding any error
  • 100% client-side — your data never leaves your browser

How to Use the YAML Validator

  1. 1

    Paste or type your YAML

    Paste your YAML content into the left-hand editor, or click "Sample YAML" to load an example document.

  2. 2

    Check the validation result

    The status banner at the bottom turns green for valid YAML or red for invalid YAML. Errors show the exact line and column.

  3. 3

    Fix errors using the context snippet

    When invalid, the right panel displays the error message and a context snippet showing the lines around the problem — use this to pinpoint the issue quickly.

  4. 4

    Copy the formatted output

    Once valid, the right panel shows the re-formatted YAML. Click "Copy" to copy it to your clipboard.

Tip: Use the "Sample YAML" button to explore multi-document formatting with --- separators, anchors, and block scalars before validating your own files.

Common Use Cases

Kubernetes & Helm

  • • Validate Deployment, Service, and ConfigMap manifests
  • • Catch indentation errors before kubectl apply
  • • Format Helm values files for readability

CI/CD Pipelines

  • • Check GitHub Actions workflow files
  • • Validate GitLab CI and CircleCI configs
  • • Spot missing colons or wrong indentation levels

Docker & Compose

  • • Validate docker-compose.yml before running services
  • • Verify multi-service network and volume configs
  • • Format compose files with consistent indentation

Application Config Files

  • • Validate config.yml for Rails, Django, or Spring Boot
  • • Check Ansible playbooks and inventory files
  • • Format Prometheus and Grafana alert rules

Static Site Generators

  • • Validate Hugo, Jekyll, and MkDocs front matter
  • • Check _config.yml and netlify.toml equivalents
  • • Format site data files before deployment

Learning & Debugging

  • • Experiment with YAML anchors and aliases
  • • Understand block scalars (literal | and folded >)
  • • Learn multi-document syntax with instant feedback

More YAML Questions Answered

What is the difference between YAML and JSON?

YAML is a superset of JSON — any valid JSON is also valid YAML. YAML adds human-friendly features like comments (#), unquoted strings, and block syntax, making it more common for configuration files.

Can I use tabs for indentation in YAML?

No. The YAML specification explicitly forbids tab characters for indentation. You must use spaces only. Mixing tabs and spaces is the most common cause of YAML parse errors.

How do I validate YAML in a CI pipeline?

Use command-line tools like yamllint (Python) or js-yaml --validate (Node.js) for automated CI checks. This online tool is ideal for quick manual validation during development.

What are YAML anchors and aliases?

Anchors (&name) mark a value for reuse and aliases (*name) reference it later. This avoids repeating identical blocks — common in large docker-compose or CI config files.

What is the maximum YAML file size this tool supports?

There is no hard file size limit enforced by this tool. Very large files (several MB) may slow down your browser tab since all processing runs client-side, but typical configuration files validate instantly.

Does this tool validate YAML schema (types and required fields)?

This tool validates YAML syntax only — it does not check against a schema. For schema validation (e.g., ensuring required Kubernetes fields are present), use a dedicated schema validator such as kubeval or JSON Schema tooling.

Is my YAML data safe to paste here?

Yes. All processing happens entirely in your browser using the js-yaml library. Nothing is sent to any server, logged, or stored. You can safely paste credentials, API keys in config snippets, or any sensitive configuration.