Format JSON5 to valid JSON
online, free & instant

JSON5 to valid JSON in three steps

No account. No upload. No nonsense.

Related JSON tools

Common questions answered

What is JSON5?

JSON5 is an extension of JSON that adds features from ECMAScript 5.1 to make it more human-friendly. JSON5 allows single-line and multi-line comments, trailing commas, single-quoted strings, unquoted object keys (when valid identifiers), hexadecimal numbers, and special values like Infinity and NaN. It was designed for configuration files where humans write and maintain JSON by hand.

This tool formats JSON5 input by normalizing it to standard JSON, then applying indentation and syntax highlighting. If you have a JSON5 configuration file (like a babel.config.json5), paste it here to get a clean, readable version. The output is strict JSON — comments and trailing commas are removed since they are not valid in the JSON specification.

{
  // user config
  name: 'Alice',
  age: 30,
  active: true,
}

{
  "name": "Alice",
  "age": 30,
  "active": true
}

Get the most out of this tool

• Use JSON5 for configuration files that need comments — tools like Babel, ESLint, and Webpack support it natively.
• This formatter strips JSON5 extensions and outputs strict JSON — useful for converting config files to standard format.
• If your JSON5 uses trailing commas, the Repair tab also handles them without needing JSON5 mode.

Understanding JSON5 and its extensions to JSON

JSON5 was created in 2012 by Aseem Mital to address the pain points developers experience when writing JSON by hand. While standard JSON is an excellent machine-generated format, it becomes tedious for humans to author and maintain — particularly the prohibition on comments and trailing commas. JSON5 is a strict superset of JSON: every valid JSON document is valid JSON5, but JSON5 allows several additional syntactic conveniences that standard JSON forbids.

Single-line comments using // and multi-line block comments using /* ... */ are perhaps the most frequently missed feature of standard JSON. Configuration files written in JSON often need to document why a value is set, what a field means, or which environment a setting applies to. JSON5 comments fill this gap, enabling self-documenting configuration files that explain their own settings inline.

Trailing commas after the last item in arrays and objects eliminate a common source of JSON syntax errors. In standard JSON, adding a new item to the end of a list requires adding a comma to the previously final item, which shows up as a confusing diff entry. In JSON5, trailing commas are allowed, so each item can independently have a trailing comma — making list additions produce single-line diffs and making the format more version-control friendly.

Unquoted object keys are another JSON5 convenience. Standard JSON requires all keys to be double-quoted strings, even when they are simple identifiers. JSON5 allows ECMAScript 5 identifier names as unquoted keys: {name: "Alice"} instead of {"name": "Alice"}. Keys that are reserved words or contain special characters still require quoting, but simple alphanumeric keys can be written without quotes.

Single-quoted strings provide an alternative to double-quoted strings, which is familiar to developers coming from JavaScript, Python, or Ruby backgrounds where single and double quotes are interchangeable. JSON5 also supports multi-line string literals — a string can span multiple lines when each line continuation is marked with a backslash, avoiding the need to embed \n escape sequences for readable multi-line content.

Numeric extensions in JSON5 include hexadecimal literals (0xFF), IEEE 754 special values (Infinity, -Infinity, NaN), and an explicit positive sign for numbers (+1.5). Standard JSON cannot represent infinity or NaN, causing JavaScript's JSON.stringify(Infinity) to produce the string "null". JSON5 provides a standards-backed way to represent these values in data files.

The practical adoption of JSON5 has been significant: Babel uses it for babel.config.json5, ESLint accepts it for configuration, and VS Code uses a JSONC variant (JSON with comments) for its settings.json. The json5 npm package provides parsing and serialization for Node.js applications. However, JSON5 is not supported by language standard libraries — Python's json module and Go's encoding/json package only handle standard JSON, requiring explicit JSON5 parser libraries.

When developers use JSON5

JSON5 pitfalls and limitations

• Using JSON5 where standard JSON is required: APIs, JSON Schema validators, and language standard libraries only accept standard JSON. JSON5 files must be converted to standard JSON before use in these contexts. Never commit JSON5 files to a repo expecting tools to parse them as standard JSON without a build step.
• Assuming NaN and Infinity are supported everywhere: While JSON5 allows NaN and Infinity, standard JSON does not. When converting JSON5 with these values to standard JSON, they must either be replaced with null, omitted, or converted to strings — decide which representation makes sense for your data before converting.
• Forgetting that unquoted keys have restrictions: JSON5 unquoted keys follow ECMAScript identifier rules — they cannot start with numbers, cannot contain hyphens, and cannot be certain reserved words. A key like my-field or 2fast must still be quoted. Check that all your unquoted keys are valid ECMAScript identifiers.
• Not stripping comments before JSON parsing: If you try to parse a JSON5 file with a standard JSON parser, comments will cause a parse error. Always use a JSON5 parser library or strip comments during a preprocessing step before passing JSON5 content to standard JSON parsers.

Additional frequently asked questions