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YAML Validator & Formatter

Validate YAML syntax and convert between YAML and JSON. All processing happens in your browser.

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YAML Validator & Formatter

Validate YAML syntax and convert between YAML and JSON. All processing happens in your browser.

InputYAML
OutputYAML
Supports multi-document YAML separated by ---
Embed code
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<p style="font-size:12px;text-align:center;margin-top:4px;">
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Powered by devcraft

How to Use YAML Validator & Formatter

  1. 1

    Paste your YAML or JSON

    Paste YAML to validate or convert to JSON, or paste JSON to convert to YAML.

  2. 2

    Choose an action

    Use Validate to check syntax, YAML to JSON to convert, or JSON to YAML to go the other direction.

  3. 3

    Review the output

    See the converted or validated result in the output panel. Errors show line numbers.

  4. 4

    Copy the result

    Click Copy to copy the output to your clipboard.

Frequently Asked Questions

No. All validation and conversion happens entirely in your browser. Your data never leaves your machine.

Yes. You can use --- separators between multiple YAML documents and they will be parsed individually.

The validator detects syntax errors like invalid indentation, duplicate keys, and malformed values, with line numbers when available.

Yes. Switch to the JSON to YAML tab, paste your JSON, and click Convert to get formatted YAML output.

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YAML: Powerful Syntax, Subtle Gotchas

YAML (YAML Ain't Markup Language) uses indentation to represent structure, making it more human-readable than JSON for configuration files. It is the standard format for Kubernetes manifests, Docker Compose files, GitHub Actions workflows, Ansible playbooks, and many CI/CD systems. But YAML's flexibility comes with pitfalls that have caused production incidents at companies of every size.

The Norway Problem and Implicit Typing

YAML 1.1 automatically interprets certain strings as non-string types. The country code "NO" becomes boolean false. "1.0" becomes a float, not a string. "on" and "off" become booleans. The version "1.2.3" stays a string, but "1.2" becomes a float. This "helpful" type inference has caused countless bugs — most famously, a list of country codes where Norway disappeared. YAML 1.2 reduced the auto-typing rules, but many parsers still default to YAML 1.1 behavior. When in doubt, quote your strings.

YAML vs. JSON for Configuration

YAML supports comments (JSON does not), multi-line strings, and anchors/aliases for reusing values — all valuable for configuration files. JSON is stricter and unambiguous, making it better for data interchange. For Kubernetes and CI/CD, YAML is the standard. For API responses and package.json-style configs, JSON is preferred. TOML (used by Cargo, pyproject.toml) offers a middle ground with explicit typing and comment support but less nesting flexibility.