YAML to JSON

Convert YAML to JSON and JSON to YAML

YAML and JSON describe the same kinds of data: mappings of keys to values, lists, text, numbers, true and false, and null. YAML is written for people, with indentation instead of brackets and room for comments. JSON is stricter, with brackets, quotes and no comments, which makes it simple for programs to read. This YAML to JSON converter turns one into the other in both directions, and on the way it checks that the input is valid, so you can also use it to validate a config file before you deploy it.

The conversion runs in a background thread of your browser, so even large files do not freeze the page, and nothing you paste is uploaded. To tidy up JSON, use the JSON formatter. To get a spreadsheet out of the result, the JSON to CSV converter takes over, and the CSV to JSON converter goes the other way.

Errors by line and column, in plain English

When the YAML is invalid, you see the line and column where the parser stopped, a short explanation of the likely cause and a button that jumps to the spot. These are the mistakes behind most broken YAML:

• Tabs for indentation. The YAML 1.2.2 spec says tab characters must not be used in indentation, because different systems treat tabs differently. Only spaces may start a line. The tool offers to replace those tabs with spaces.
• Indentation that does not line up. All keys of one mapping, and all items of one list, have to start in the same column. One space too many or too few moves a line into a different level.
• Duplicate keys. The spec defines a mapping as a set of key and value pairs in which each key is unique, so a second name: in the same mapping is an error, not an update.
• Unclosed quotes. A string that opens with a quote and never closes swallows the lines after it. The error points to where the string starts.
• A colon inside a value. In title: Note: read me, the second colon followed by a space starts another key. Put the value in quotes.
• Reserved characters. The spec reserves @ and the backtick for future use, so a value cannot start with them unless it is quoted.

Pasting JSON into the YAML side works too, because YAML 1.2 was designed as a superset of JSON. In the other direction the input must be strict JSON, and errors such as a trailing comma or single quotes are reported with their position.

YAML 1.1 versus YAML 1.2: yes, no, on and off

The YAML 1.2.2 spec says the 1.2 release focused on making YAML a strict superset of JSON and removed many of the problematic implicit typing rules of earlier versions. Under the core schema that this converter uses by default, only true, True, TRUE, false, False and FALSE are booleans, and octal numbers need a 0o prefix. Many tools still follow YAML 1.1, though, and there the same text can mean something else. The documentation of the yaml library that powers this tool lists the differences:

The second row matters for lists of country codes: under YAML 1.1, Norway's code NO turns into false. A key named on becomes true in the same way. This converter reads YAML 1.2, and whenever your input contains values that a YAML 1.1 parser would read differently, it lists them with their line and both readings. Switch YAML version to 1.1 to see the output an older parser would produce. When you write YAML, leave Quote values YAML 1.1 parsers misread on, and words such as "no" and "on" get quotes, so every parser keeps them as text.

Multiple documents, anchors and merge keys

One YAML file can hold several documents, each starting with a line of three dashes (---). The spec treats every document as completely independent. Choose All as a JSON array to get all of them in one array, or One at a time to convert a single document. Going from JSON to YAML, Array items as separate documents writes each item of a top-level array as its own document.

An anchor (&name) marks a value, and an alias (*name) repeats it later. According to the spec, an alias refers to the most recent value with that anchor before it, and an alias whose anchor does not come earlier in the document is an error. JSON has no references, so each alias is replaced by a full copy. Merge keys (<<: *defaults) copy the entries of another mapping into the current one. The yaml library documentation notes that merge keys are a YAML 1.1 feature that is not part of the 1.2 spec. Because many config files rely on them, they are applied here unless you switch Merge keys off. Aliases can also be abused to make a small file expand into a huge amount of data. The yaml library guards against such expansion attacks by limiting how often aliases may repeat, and the tool then stops with a message instead of hanging.

What JSON cannot hold

• Comments are left out, because JSON, as defined in RFC 8259, has no comments.
• JSON keys are always text. Keys such as 1, true or null become "1", "true" and "null", and a notice tells you.
• .inf and .nan become null, because JSON has no infinity or NaN.
• Custom tags like !Ref are dropped and their values kept. The program that reads the YAML gives them their meaning.
• Whole numbers keep every digit. RFC 8259 warns that many programs read numbers as 64-bit floating point values, so a very long ID may still lose digits in the program that reads the JSON.

How to use the YAML to JSON converter

1. 1Pick YAML to JSON or JSON to YAML, then paste your text, drop a file on the box or open one.
2. 2If an error appears, read the cause, jump to the line and column, and fix it. The result updates as you type.
3. 3Choose the format: indent and minified JSON, or indent and quotes for YAML. Check the notes on YAML 1.1 values.
4. 4Copy the result or download it. Swap sends the result back as input, so you can check the round trip.

Frequently asked questions