YAML Validator & Formatter

YAML is the configuration language of modern infrastructure — CI pipelines, Kubernetes manifests, app settings — and its greatest strength is also its greatest trap: structure is expressed entirely by indentation, so a single misaligned line silently changes meaning or breaks the file. This validator checks the YAML structures developers use most — nested mappings, lists, scalars, quoted strings, numbers and booleans — and reports problems plainly: tabs where spaces belong, inconsistent indentation, keys without values, and lines that do not parse as mappings or list items. Valid YAML is also reformatted with consistent two-space indentation, so a messy file comes out clean and readable. It is a focused tool, not a full YAML parser: exotic features such as anchors, multi-line blocks and complex flow styles are outside its scope, and the guide says so plainly — but for everyday configuration files, it catches the errors that waste the most debugging time.

How to Use the YAML Validator & Formatter

1. Paste your YAML into the input box.
2. Press Validate & Format and read the verdict.
3. If errors are listed, fix the reported lines and validate again.
4. Read the formatted output to confirm the structure is what you intended.
5. Copy the formatted YAML into your configuration file.

Key Features

• Validates nested mappings, lists and scalar values
• Catches tabs, inconsistent indentation and malformed lines
• Reformats valid YAML with consistent two-space indentation
• Handles quoted strings, numbers, booleans and null
• Free, instant and entirely in your browser

Best Practices and Tips

• Use spaces, never tabs: YAML forbids tabs for indentation, and this is the single most common YAML error.
• Keep indentation consistent at two spaces per level; mixing two and four spaces breaks nesting.
• Quote values containing colons, hashes or leading special characters, or the parser will misread them.
• Validate before committing: a broken YAML file can fail an entire deployment pipeline.
• For very large manifests, validate one document section at a time to localise errors faster.

Common Mistakes to Avoid

• Indenting with tabs, which YAML rejects outright.
• Mixing indentation widths in one file, which creates phantom nesting levels.
• Leaving a key without a value or colon, which is not a valid mapping entry.
• Using unquoted special values such as yes, no and on, which YAML may read as booleans.

Frequently Asked Questions

What does this YAML validator check?

It parses the common YAML subset used in configuration files: nested mappings, lists, plain and quoted scalars, numbers, booleans and null. It reports tabs, inconsistent indentation, malformed lines and structural problems, and reformats valid input.

Why are tabs not allowed in YAML?

The YAML specification forbids tabs for indentation because tab widths vary between editors, making the same file mean different things in different tools. Spaces are the only reliable indentation, and this validator flags any tab it finds.

Does it support anchors, aliases and multi-line blocks?

No. Those advanced features are outside this focused validator scope. Files using them may be reported as unsupported rather than invalid — check such files with a full YAML parser in your toolchain.

How is the formatted output produced?

Valid input is re-emitted with consistent two-space indentation per nesting level, list items aligned under their parent key, and scalar values preserved. The result is semantically identical and far easier to read.

Is the YAML validator free?

Yes — free, unlimited and no sign-up required.

Related Tools

• YAML to JSON Converter – parses YAML properly and outputs clean, formatted JSON
• JSON to YAML Converter – Convert JSON into clean readable YAML
• TOML to JSON Converter – TOML configuration converted to JSON
• JSON Formatter & Validator – beautifies JSON and pinpoints syntax errors when it will not parse