JSON Formatter
Format, validate, and minify JSON data instantly. Detect syntax errors with precise line and column information.
How do I use JSON Formatter?
Paste raw or minified JSON into the left editor, drop a .json file (up to 100MB), or click 'Sample' to load a starter payload.
Choose your indentation level (2 Spaces, 4 Spaces, or Minify) or switch to the interactive Tree View tab to inspect nested objects.
Review any RFC 8259 syntax errors with exact line and column pointers, then copy or download the formatted JSON.
What features does JSON Formatter offer?
Format, validate, beautify, and minify JSON data
Precise syntax error line & column pointers
Multiple indentation modes (2 spaces, 4 spaces, compact)
100% client-side privacy guarantee — zero data uploads
RFC 8259 / ECMA-404 JSON Grammar & Syntax Specification
Strict JSON parsers enforce RFC 8259 grammar rules. Unlike JavaScript object literals, JSON requires double-quoted property keys and forbids trailing commas, comments, and undefined values.
| Syntax Element | RFC 8259 Standard JSON | JS Object Literal | Common Parser Error |
|---|---|---|---|
| Object Keys | Double quotes required ("id") | Unquoted or single quotes allowed | Expected property name or '}' |
| Trailing Commas | Strictly forbidden after last item | Allowed in ES5+ | Unexpected token } or ] |
| Numbers | Base-10 only; no NaN, Infinity, or 0xFF | Hex, Octal, NaN, Infinity valid | Unexpected token N in JSON |
| Comments | Not supported (// or /* */ invalid) | Single and multi-line supported | Unexpected token / in JSON |
Frequently Asked Questions about JSON Formatter
Why does JSON.parse fail with 'Unexpected token } in JSON' on a trailing comma?
RFC 8259 Section 4 forbids a comma after the final key-value pair in an object or the final element in an array. Remove the comma immediately preceding the closing `}` or `]` to pass strict validation.
Why do 64-bit integer IDs (like Snowflake IDs) lose precision in browser JSON parsers?
JavaScript's native `JSON.parse()` converts all numbers into IEEE 754 double-precision floats, which only guarantee exact integer precision up to `Number.MAX_SAFE_INTEGER` (`9,007,199,254,740,991` or $2^{53}-1$). Serialize 64-bit IDs as JSON strings to prevent rounding.
What is the maximum JSON payload size supported in the browser?
Payloads up to 100MB are supported in local browser memory. For payloads exceeding 5MB, switch from Tree View to raw formatted text mode to avoid DOM node allocation overhead.
How do I escape control characters like newlines or tabs inside a JSON string?
Raw unescaped control characters (`U+0000` through `U+001F`) are illegal inside JSON string literals. Replace literal line breaks with `\n`, carriage returns with `\r`, and tabs with `\t`.
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