YAML to JSON and back, YAML validation with line numbers and YAML 1.1 warnings.
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Three things in one place: YAML to JSON, JSON to YAML, and format YAML, which reads a file and writes it back in one consistent style. Every conversion is also a validation: a YAML error is reported with its line and column and a button that puts the cursor on it. The parser is written for this site and runs in your browser, so configuration files with secrets in them never leave your device.
The common YAML 1.2 subset that configuration files use: nested mappings and lists (including the - key: value style and lists written at the same indentation as their key), inline [a, b] and {a: 1} collections, plain, 'single' and "double" quoted strings with every escape, literal | and folded > blocks with the - and + chomping indicators, anchors (&name), aliases (*name), the << merge key, the standard tags (!!str, !!int, !!float, !!bool, !!null) and several documents separated by ---. Several documents become a JSON array with one item per document.
Not supported, and reported as an error rather than guessed: complex keys (? key or a list used as a key), custom tags such as !Ref from CloudFormation, and %TAG directives. Comments are dropped, because JSON has no comments.
The parser follows the YAML 1.2 core schema: true and false are booleans, ~ and null are null, numbers are numbers, and everything else is a string. It is checked against the examples in chapter 2 of the YAML 1.2.2 specification and against an independent YAML library on dozens of edge cases.
Many tools still read YAML with 1.1 rules (PyYAML, older Ruby and Go libraries, some CI systems). The two versions disagree on values people write every day:
false (the "Norway problem").The tool warns with the line number whenever your file contains one of these, and the JSON to YAML direction always quotes such strings ("NO", "0755", "12:30", "2024-01-02") so the result means the same thing to every parser.
.inf and .nan have no JSON form and become null, with a note saying how many.Tabs are not allowed for indentation in YAML, which is the most common error after a copy and paste; the error message names the line. Anchors are expanded in the JSON, and a document that expands to an absurd size (the "billion laughs" attack) is stopped instead of freezing the tab. For more on indentation, anchors and safe quoting, read YAML pitfalls and how to convert safely. To check the JSON side, use the JSON formatter.
In YAML 1.1, NO, no, yes, on and off are booleans. YAML 1.2 changed that, but many parsers still use 1.1 rules. This tool reads YAML 1.2, so NO stays a string, and it warns you because another tool might not. Write 'NO' in quotes to be safe everywhere.
The YAML specification forbids tabs for indentation, because their width is ambiguous. Replace them with spaces. Tabs inside a value or after a colon are allowed.
They are dropped. JSON has no comments, and when formatting YAML the tool rebuilds the file from its data, so comments are not kept. Keep the original if the comments matter.
A file with several documents separated by --- becomes one JSON array, with one item per document. An empty document becomes null.
Yes. Aliases are replaced by a copy of the anchored value, and << copies the keys of one or more mappings that are not already set. Keys written explicitly always win.