About

Standard JSON (RFC 8259) enforces strict rules: double-quoted keys, no trailing commas, no comments. Real-world development demands flexibility. Config files use JSON5 or JSONC. JavaScript source expects unquoted keys and single-quote strings. Pasting RFC-strict JSON into a .js file triggers linter errors. Manually reformatting a 500-line config is error-prone and slow. This tool parses valid JSON via the native JSON.parse engine, then re-serializes it through a custom formatter that applies your chosen syntax rules. It does not use regex-based find-and-replace. It rebuilds the output from the parsed AST, guaranteeing structural correctness regardless of the target style.

Limitations: input must be valid JSON. JSON5 or JS-object input is not accepted because the browser's native parser rejects it. The output in non-standard formats (single quotes, trailing commas) is syntactically valid JavaScript but not valid JSON. If you need to feed the result back into a strict JSON parser, keep double quotes and disable trailing commas. Key sorting uses localeCompare with Unicode-aware ordering, which may differ from ASCII-sort tools.

Formulas

The conversion pipeline follows a deterministic three-stage process:

input → JSON.parse(input) → AST → serialize(AST, options) → output

Where AST is the native JavaScript object tree produced by the parser. The serialize function performs a recursive depth-first traversal. At each node, it applies the following rule set:

{

quoteKey(k) = k if k matches /^[a-zA-Z_$][a-zA-Z0-9_$]*$/ ∧ unquoted = TRUEquoteKey(k) = Q + k + Q otherwise

Where Q is the selected quote character (", ', or `). Trailing comma injection appends a comma after the last element of every array and object. Key sorting applies Array.prototype.sort with localeCompare before serialization. Indentation depth d at nesting level n equals d = n × indentSize.

Reference Data

Syntax Feature	Standard JSON (RFC 8259)	JSON5	JSONC	JS Object Literal
Key Quoting	Required (double)	Optional	Required (double)	Optional
String Quotes	Double only	Single or Double	Double only	Single, Double, Backtick
Trailing Commas	Forbidden	Allowed	Forbidden	Allowed
Comments	Forbidden	// line and /* block */	// line and /* block */	Allowed
Unquoted Keys	Forbidden	Allowed (identifiers)	Forbidden	Allowed (identifiers)
Hexadecimal Numbers	Forbidden	Allowed (0xFF)	Forbidden	Allowed
Infinity / NaN	Forbidden	Allowed	Forbidden	Allowed
Multiline Strings	Forbidden (use \n)	Allowed (backslash)	Forbidden	Template literals
Root Value Types	Any JSON value	Any JSON value	Any JSON value	Object or Array
File Extension	.json	.json5	.jsonc	.js / .mjs
MIME Type	application/json	application/json5	application/json	application/javascript
Parser Support	All languages	Node.js (json5 pkg)	VS Code, TypeScript	JavaScript only
Spec Status	IETF Standard	Community Draft	De facto (Microsoft)	ECMAScript Standard
Use Case	APIs, data exchange	Config files	VS Code settings	Source code constants
Max Nesting (typical)	Unlimited (parser-dependent)	Unlimited	Unlimited	Unlimited
Unicode Escapes	\uXXXX	\uXXXX	\uXXXX	\u{XXXXX} extended
Date Handling	String only	String only	String only	new Date() allowed

Frequently Asked Questions

No. RFC 8259 mandates double-quoted strings and forbids trailing commas. Output with single quotes or trailing commas is valid JavaScript but will fail if fed into a strict JSON parser such as JSON.parse. Use these styles only for config files (JSON5) or JS source code.

A key is left unquoted only if it matches the ECMAScript IdentifierName pattern: starts with a letter, underscore, or dollar sign, followed by alphanumeric characters, underscores, or dollar signs. Keys containing spaces, hyphens, dots, or starting with digits are always quoted regardless of the setting. The regex used is /^[a-zA-Z_$][a-zA-Z0-9_$]*$/.

Yes. Sorting is applied recursively at every nesting level. Each object's keys are independently sorted using String.prototype.localeCompare with the "en" locale. Array element order is never modified because arrays are ordered collections by definition.

The native JSON.parse resolves all \uXXXX escapes into their actual Unicode characters. The custom serializer then re-encodes only characters that require escaping in the target quote style (the quote character itself, backslash, and control characters U+0000 through U+001F). All other Unicode characters pass through as literal UTF-8.

The tool processes input in the browser's main thread. For files under 1 MB, conversion is near-instantaneous. Between 1 and 5 MB, expect a brief pause. Above 5 MB, the browser may become unresponsive. For very large datasets, consider using a CLI tool like jq or splitting the file first.

In K&R (Kernighan & Ritchie) style, the opening brace sits on the same line as the key or statement: "key": {. In Allman style, the opening brace drops to its own line, aligned with the parent indentation level. Both produce semantically identical data. The choice is purely aesthetic and should match your project's code style guide.