YAML (YAML Ain't Markup Language) is a human-readable data serialization format commonly used for configuration files. It uses indentation to represent structure and is widely used in Kubernetes, Docker Compose, GitHub Actions, Ansible, and many other tools.

How do I validate YAML?

Paste your YAML into the input field and click Validate or Format. If the YAML contains errors (wrong indentation, duplicate keys, invalid characters), an error message will appear with the line number and description of the problem.

What is the difference between YAML and JSON?

YAML is a superset of JSON — valid JSON is valid YAML. YAML uses indentation instead of braces and brackets, supports comments (with #), and allows multi-line strings. JSON is more strict but easier to parse programmatically. YAML is preferred for config files; JSON for APIs.

Can I convert YAML to JSON?

Yes. Use the 'YAML → JSON' button to convert your YAML to formatted JSON. This is useful when you need to pass YAML configuration data to a JSON API, or when debugging YAML parsing issues by seeing the equivalent JSON structure.

YAML Formatter & Validator

Format, validate and convert YAML — free, instant, runs in your browser

Input YAML

Formatted YAML

What is YAML?

Human-readable config format

YAML (YAML Ain't Markup Language) uses indentation to represent nested structure — no curly braces or brackets. A key: value on its own line, lists with -, and comments with #. This makes it easy to read and write by hand compared to JSON or XML.

Widely used in DevOps

YAML is the standard format for Kubernetes manifests, Docker Compose files, GitHub Actions workflows, Ansible playbooks, Helm charts, GitLab CI/CD, CircleCI, and virtually every modern DevOps tool. Understanding YAML is essential for infrastructure work.

Superset of JSON

Every valid JSON document is also valid YAML. YAML extends JSON with comments, multi-line strings, anchors and aliases (for reusing values), and a more relaxed syntax for strings. You can convert any JSON to YAML and back without losing data.

Common gotchas

YAML is indent-sensitive — mixing tabs and spaces causes errors. Strings containing :, #, or special characters must be quoted. yes, no, true, null are parsed as booleans/null unless quoted. This formatter catches all these issues.

Frequently Asked Questions

YAML (YAML Ain't Markup Language) is a human-readable data serialization format designed for configuration files and data exchange. Use YAML when humans need to read and write the files frequently — config files, CI/CD pipelines, infrastructure definitions. Use JSON for machine-to-machine communication where parsing speed matters more than readability. YAML is the default choice for Kubernetes, Ansible, GitHub Actions, and Docker Compose.

YAML is extremely sensitive to indentation. The most common causes: (1) mixing tabs and spaces — YAML only allows spaces, never tabs; (2) inconsistent indentation levels — every level must use the same number of spaces; (3) copy-pasting from sources that converted spaces to tabs. This formatter automatically normalizes indentation. If you see a tab character error, replace all tabs with spaces using your editor's "convert indentation" feature.

YAML is a superset of JSON — valid JSON is always valid YAML. Key differences: YAML uses indentation instead of braces, allows comments (with #), supports multi-line strings with | and >, has anchors/aliases for value reuse, and doesn't require quotes around most strings. JSON is stricter, faster to parse, and more widely supported as a data interchange format. YAML is preferred for configuration files that humans edit regularly.

Paste your YAML into the input field and click the YAML → JSON button. The tool uses the js-yaml library to parse your YAML into a JavaScript object, then JSON.stringify to produce formatted JSON. Note that some YAML features (like comments and anchors) don't have JSON equivalents and will be stripped from the output.

In YAML 1.1 (used by many tools), bare words like yes, no, on, off are parsed as booleans. This surprises developers using country codes (NO for Norway) or simple yes/no values as strings. YAML 1.2 (used by this tool) only treats true and false as booleans. To be safe, always quote strings that could be misinterpreted: country: "NO".

Yes. All YAML parsing and formatting runs in your browser using the js-yaml library loaded from a CDN. No data is sent to any server. Your Kubernetes secrets, API keys in config files, and other sensitive YAML content never leaves your device. You can verify this by checking the browser DevTools Network tab — no requests are made when you format YAML.