Free Online YAML Formatter & Validator
Format, validate, and convert YAML online. Pretty-print with 2 or 4-space indent, validate syntax, and convert between YAML and JSON. Free, 100% client-side.
100% Client-Side · Your data never leaves your browserHow to Use YAML Formatter & Validator
Paste your YAML into the Input area, then choose a mode from the toolbar:
- Format YAML — parses and re-serializes your YAML with consistent indentation. Choose 2 spaces or 4 spaces to match your project's convention.
- Validate — checks whether the YAML is syntactically correct without modifying it. A green banner confirms valid YAML; a red banner shows the exact parse error.
- YAML → JSON — converts your YAML document into pretty-printed JSON. Useful when you need to pass YAML data to a JSON-only API or tool.
- JSON → YAML — converts a JSON object or array into clean YAML. Great for migrating configuration files from JSON-based tools to YAML-based ones.
Click the active mode button or press Ctrl/Cmd+Enter to run. Use the Copy button to copy the full output. Press Ctrl/Cmd+K to clear both input and output.
Frequently Asked Questions
What is YAML and why use a formatter?
YAML (YAML Ain't Markup Language) is a human-readable data serialization format widely used for configuration files — Kubernetes, Docker Compose, GitHub Actions, and many more. A formatter automatically fixes indentation and spacing so the file is both valid and easy to read.
What indentation does YAML require?
YAML uses spaces for indentation — never tabs. The specification does not mandate a specific number of spaces, but 2 spaces is the most common convention in the ecosystem. This tool lets you choose between 2 and 4 spaces.
What is the difference between "Format YAML" and "Validate"?
"Format YAML" parses your input and re-serializes it with consistent indentation, which also implicitly validates it. "Validate" only checks whether the YAML is syntactically correct and returns a clear error message if not — it does not alter the content.
Can I convert YAML to JSON and back?
Yes. Use "YAML → JSON" to parse YAML and output it as pretty-printed JSON. Use "JSON → YAML" to go in the other direction. The conversion preserves all data types including strings, numbers, booleans, nulls, arrays, and objects.
Is my YAML data sent to a server?
No. All processing happens entirely in your browser using the js-yaml library. Your configuration files and data never leave your machine.
Why does my formatted YAML look different from the original?
YAML allows multiple ways to represent the same data (block style vs. flow style, quoted vs. unquoted strings, etc.). The formatter normalizes everything to the canonical block style, which is the most readable and most commonly expected format for config files.