YAML Formatter & Validator

The YAML Formatter & Validator is a free online tool that checks your YAML for syntax errors and re-emits it as clean, consistently indented, human-readable YAML. Paste your document, and it instantly validates the structure, points to the line and column of the first problem when something is wrong, and beautifies the rest.

It runs completely in your browser, so your configuration files, secrets, and data never leave your machine. There are no uploads, no accounts, and no server-side processing.

How to format and validate YAML

1. Paste or type your YAML into the input panel on the left.
2. Choose your indent size (2 or 4 spaces), whether to sort keys, and block or flow output style.
3. Click Format & Validate.
4. Read the status bar: a green message confirms valid YAML, while a red message shows the error with its line and column.
5. Use Copy or Download to grab the cleaned-up result.

What is YAML?

YAML ("YAML Ain't Markup Language") is a human-friendly data serialization format used heavily for configuration files in tools like Kubernetes, Docker Compose, GitHub Actions, and Ansible. Because YAML relies on indentation instead of braces, a single misplaced space can break an entire file — which is exactly why a dedicated validator saves so much time.

Why use a YAML validator?

YAML's whitespace sensitivity makes errors easy to introduce and hard to spot by eye. A tab where a space belongs, an unquoted colon inside a value, or an inconsistent indent level will all cause a parser to fail. This tool surfaces those issues with a precise location so you can fix them in seconds rather than scanning line by line.

YAML Formatter features

• Strict validation that reports the line and column of the first syntax error.
• Configurable indentation of 2 or 4 spaces for consistent, diff-friendly output.
• Sort keys alphabetically to normalize mappings across teams and reduce noisy version-control diffs.
• Block or flow output — pretty multi-line block style, or a compact single-line flow form.
• Multi-document support for YAML streams separated by ---.
• Copy and Download the formatted result as a .yaml file.

When to use block vs. flow style

Block style is the default and the right choice for config files you read and edit by hand, since each key sits on its own indented line. Flow style collapses structures into a compact {key: value, list: [1, 2]} form, which is handy for embedding small snippets inline or minimizing a payload. Reach for flow when brevity matters and block when readability does.

YAML and JSON are closely related — in fact, valid JSON is valid YAML. If you work across both, you may also want the JSON Formatter to beautify JSON, the JSON Minifier to compress it for production, or the JSON to YAML Converter when you need to move data between the two formats. Teams that also touch database work often keep the SQL Formatter & Beautifier nearby for the same reason: consistent, readable formatting cuts down on review friction.

Frequently Asked Questions

Is my YAML data uploaded to a server?

No. All validation and formatting happen locally in your browser using client-side JavaScript. Your YAML is never sent to, stored on, or seen by any server.

Why does my YAML fail with an indentation error?

YAML uses indentation to define structure and does not allow tab characters for indentation. Mixing tabs and spaces, or using inconsistent indent levels within the same block, will cause a parse error. The tool shows the exact line and column so you can correct it quickly.

What does sorting keys do?

Sorting arranges the keys of every mapping in alphabetical order. This produces a canonical, predictable layout that makes version-control diffs smaller and helps teams compare configuration files consistently.

Does the tool support multiple YAML documents?

Yes. YAML streams that contain multiple documents separated by --- are fully supported. Each document is validated and formatted, and the separators are preserved in the output.

What is the difference between block and flow style?

Block style spreads data across indented multi-line structures and is the most readable for configuration files. Flow style uses a compact inline form with braces and brackets, which is useful for short snippets or minimizing size.

Can I convert between YAML and JSON here?

This tool focuses on formatting and validating YAML. To convert data between the two formats, use a dedicated JSON to YAML converter, since valid JSON is also valid YAML.