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Free Online YAML Formatter & Validator — Pretty Print YAML Instantly

Paste YAML to format, validate, and convert it to JSON. Adjust indentation, catch syntax errors, and copy clean output — all in your browser.

Valid YAML
Input
Output

What Is YAML?

YAML (YAML Ain't Markup Language) is a human-friendly data serialization format used for configuration files, CI/CD pipelines, Kubernetes manifests, and API definitions. It relies on indentation to express hierarchy rather than braces or brackets.

Because YAML is whitespace-sensitive, a misplaced space can break an entire configuration. This tool parses your input with a strict YAML 1.2 parser, highlights any errors, and re-formats the content with consistent indentation so you can spot structural issues immediately.

The YAML to JSON conversion is useful when you need to paste config into a system that only accepts JSON, or when you want to verify that your YAML parses to the data structure you expect.

How to Use

  1. Paste your YAML (or JSON) into the input area.
  2. Select a mode: Format, YAML → JSON, or JSON → YAML.
  3. Choose an indentation level (2, 4, or 8 spaces).
  4. The output updates instantly. Check the status indicator for validation.
  5. Click Copy to grab the formatted result.

When You Need This

Cleaning up Kubernetes manifests

After copy-pasting YAML from Stack Overflow or docs, indentation is often inconsistent. Paste it here to normalize everything to 2-space indent before applying to your cluster.

Debugging CI/CD pipeline config

GitHub Actions, GitLab CI, and CircleCI all use YAML. When a pipeline fails with a cryptic parse error, paste the file here to see exactly which line has the syntax issue.

Converting config formats

Some tools accept JSON but not YAML (or vice versa). Use the conversion modes to switch formats without manually rewriting the structure.

Code review prep

Before submitting a PR that touches YAML config, format it through this tool to ensure consistent style and catch errors the linter might miss.

YAML Best Practices

1.

Use consistent indentation

Pick 2 spaces and stick with it across your project. Mixing tabs and spaces in YAML is a guaranteed parse failure.

2.

Quote strings that look like other types

Values like "yes", "no", "on", "off", "1.0" can be interpreted as booleans or numbers. Wrap them in quotes to preserve the string type.

3.

Use anchors and aliases for repeated blocks

YAML supports &anchor and *alias syntax to avoid duplicating configuration blocks. This keeps files DRY and easier to maintain.

4.

Validate before deploying

A single bad indent in a Kubernetes manifest can cause silent misconfiguration. Always validate YAML before applying to production.

Examples

Format nested config

Takes inconsistently indented YAML and normalizes it.

Input

server:
    host: localhost
    port: 8080
database:
      name: myapp

Output

server:
  host: localhost
  port: 8080
database:
  name: myapp

YAML to JSON

Converts YAML config to equivalent JSON.

Input

name: app
version: 1.0
features:
  - auth
  - logging

Output

{
  "name": "app",
  "version": 1,
  "features": ["auth", "logging"]
}

Limitations

  • Does not support YAML anchors and aliases (&anchor / *alias) — these are parsed but not resolved during formatting.
  • Multi-document YAML files (separated by ---) are handled as a single block, not formatted individually.
  • Maximum input size limited by browser memory. Files over 5MB may cause slowdowns.
  • Cannot validate YAML against a schema (like JSON Schema for YAML). It only checks syntax.

Features

  • Format YAML with configurable indentation (2, 4, or 8 spaces)
  • Real-time validation with error messages
  • YAML to JSON bidirectional conversion
  • Instant output as you type — no submit button needed
  • One-click copy for formatted results
  • 100% client-side processing, your data stays local

FAQ

Is my YAML data sent to a server?

No. All parsing and formatting happens in your browser using JavaScript. No network requests are made after the page loads.

Which YAML specification does this support?

The tool uses the yaml npm package which implements YAML 1.2 — the latest specification. It handles anchors, aliases, multiline strings, and all standard YAML features.

Can it handle large YAML files?

It works well with files up to a few MB. For very large files (10MB+), parsing may take a moment since everything runs in a single browser thread.

Why does my YAML show as invalid?

Common causes: mixing tabs and spaces, inconsistent indentation depth, unquoted special characters (like colons in values), or duplicate keys at the same level.

Does the JSON conversion preserve comments?

No. JSON does not support comments, so YAML comments are lost during conversion. Use the Format mode if you need to keep comments intact.

Content last reviewed: June 2026

Your Privacy

All YAML processing happens entirely in your browser. No data is uploaded to any server. Your configuration files never leave your device.

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