YAML Formatter and Validator
Format, validate, and pretty-print YAML data online. Fix syntax errors and convert YAML to JSON.
Input YAML
Output
What is YAML and why format it?
YAML (YAML Ain't Markup Language) is a human-readable data serialization format used in configuration files, CI/CD pipelines, Docker Compose, Kubernetes manifests, and API definitions. Unlike JSON, YAML uses indentation and line breaks instead of braces and commas, making it easier to read but harder to validate manually.
Formatting YAML ensures consistent indentation (2 spaces by convention), correct key-value syntax, and proper list markers. Unformatted YAML causes silent parsing errors in tools like Ansible, Helm, and GitHub Actions. A formatter catches these issues before deployment.
This tool parses YAML in the browser using a lightweight YAML parser. It validates syntax, fixes indentation, and converts to JSON when needed. For large files (over 10,000 lines), consider using a local editor like VS Code with the YAML extension for syntax highlighting and schema validation. Read the JSON Formatter for working with JSON data, and the CSV to JSON tool for converting tabular data.
Common YAML syntax mistakes
Missing the space after a colon: key:value should be key: value. Wrong indentation level: each nested level must be exactly 2 spaces deeper than its parent. Using tabs instead of spaces: YAML does not allow tab characters for indentation. Mixing list styles: stay consistent with either - item or item: inline notation.
Unquoted strings with special characters: values containing colons, brackets, or leading zeros need quotes. Forgetting the document separator --- at the top of multi-document files. Using # inside unquoted strings: the hash starts a comment unless the value is quoted.
Fix invalid JSON and YAML errors
Common JSON syntax errors: trailing commas after the last property, unquoted keys, single quotes instead of double quotes, missing colons between key and value, and comments (JSON does not support comments). The formatter above highlights error lines and auto-indents valid structures. For YAML, watch for indentation inconsistencies (use spaces, never tabs), missing colons, and incorrect list formatting.
To debug invalid JSON, paste the raw string into the formatter and read the error message — it usually identifies the exact character position. For YAML validation, convert to JSON first using this tool; if conversion fails, the error points to the YAML line that needs fixing. ToolZone also offers a JSON to Excel converter for inspecting structured data visually.
YAML formatting tips
YAML is sensitive to indentation, so use spaces consistently and avoid mixing tabs with spaces. Lists, nested mappings, quoted strings, booleans, and multi-line values can all change meaning when indentation shifts. A formatter helps make the structure readable, but you should still check the output before using it in deployment files or automation.
Quote values that look like dates, numbers with leading zeros, or words such as yes and no when they must remain strings. For app workflows that require JSON, use the YAML to JSON Converter. For API payload inspection, use the JSON Formatter.