DevBolt
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How do I format and validate YAML online?

Paste your YAML and click Format to pretty-print it with consistent indentation. The tool validates your YAML in real time, catching syntax errors like bad indentation, duplicate keys, and invalid characters. You can also minify YAML into compact form. Everything runs in your browser — your data never leaves your device.

Format messy YAML
Input
name: my-app
version:   1.0
deps:
  - express
  -    cors
  - dotenv
Output
name: my-app
version: 1.0
deps:
  - express
  - cors
  - dotenv
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YAML Validator & Formatter

Validate, format, beautify, and minify YAML documents instantly. Perfect for Kubernetes manifests, Docker Compose files, CI/CD configs, and more.

About YAML Formatting

YAML (YAML Ain't Markup Language) is a human-readable data serialization format widely used for configuration files in Kubernetes, Docker Compose, GitHub Actions, Ansible, and more.

Validation: Checks for correct YAML syntax including proper indentation, valid key-value pairs, correct use of colons and dashes, and proper quoting. Reports the exact line and column of errors.

Format: Parses and re-serializes your YAML with consistent indentation. Optionally sorts keys alphabetically for easier scanning and diff-friendly output.

Minify: Converts block-style YAML to compact flow style, reducing file size while preserving all data. Useful for embedding YAML in scripts or reducing payload size.

Everything runs in your browser — no data is sent over the network.

Tips & Best Practices

Pro Tip

Use 2-space indentation for YAML — it's the de facto standard

Kubernetes, Docker Compose, GitHub Actions, and Ansible all use 2-space indentation in their documentation and examples. Using tabs in YAML is a syntax error. Using 4 spaces works but doubles visual nesting depth. Stick with 2 spaces to match ecosystem conventions and keep deeply nested configs readable.

Common Pitfall

YAML treats 'no', 'off', and 'false' as boolean false

A country code field with value NO (Norway), or a feature flag named 'off' will be silently coerced to boolean false. YAML 1.1 also treats y/n, on/off as booleans. Always quote ambiguous string values: country: "NO", mode: "off". YAML 1.2 is stricter but many parsers still default to 1.1 behavior.

Security Note

YAML anchors can cause exponential memory consumption

YAML anchors (&) and aliases (*) enable reuse, but a billion laughs attack uses nested anchors to expand a small document into gigabytes: a: &a [*b,*b], b: &b [*c,*c]... Set recursion depth limits and maximum document size in your YAML parser. Most libraries have these options but leave them disabled by default.

Real-World Example

Multi-line strings: use | for literal, > for folded

The | (pipe) preserves newlines exactly as written — ideal for scripts, SQL, and code blocks. The > (greater-than) folds newlines into spaces, creating paragraphs — ideal for descriptions and long text. Add - to strip trailing newlines (|-, >-) or + to preserve them (|+, >+).

Frequently Asked Questions

How do I validate YAML syntax online?
Paste your YAML document and the tool parses it instantly, highlighting syntax errors with line numbers. Common errors include incorrect indentation (YAML requires spaces not tabs), missing colons after keys, unquoted special characters, and inconsistent list formatting. Valid YAML is reformatted with consistent indentation. DevBolt processes everything in your browser, safe for validating Kubernetes manifests, Docker Compose files, and configs with sensitive values.
What are the most common YAML syntax errors?
Most YAML errors involve indentation: using tabs instead of spaces causes parse failures. Other mistakes include forgetting the space after colons (name:value instead of name: value), unquoted strings with special characters, duplicate keys, and confusion between block scalar indicators (| for literal, > for folded). The 'Norway problem' where yes, no, on, off are parsed as booleans instead of strings is a persistent source of subtle bugs. Always quote ambiguous values.
When should I use YAML instead of JSON for configuration?
Use YAML for configuration where readability, comments, and editability matter. YAML's indentation syntax is cleaner for nested structures and comment support is essential for documenting complex configs. Kubernetes, Docker Compose, GitHub Actions, GitLab CI, and Ansible use YAML. Use JSON for strict machine parsing and API data interchange. YAML is a superset of JSON, so valid JSON files are also valid YAML.

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