JSON formatter and syntax validator that preserves number text

Worked result

The JSON is valid; the integer text remains 9007199254740993.

1. Validate the input using JSON syntax rules.
2. Retain each string and number token exactly as entered.
3. Insert indentation only between tokens, outside quoted strings.

Format a JSON object with a long integer

The identifier below is larger than the largest exactly representable JavaScript integer. It should not silently change during formatting.

Input:
{"name":"Ithy","values":[3,8],"id":9007199254740993}

Formatted:
{
  "name": "Ithy",
  "values": [
    3,
    8
  ],
  "id": 9007199254740993
}

Formatting can preserve a number’s spelling even when another application cannot interpret that number exactly. A consumer’s numeric model is a separate concern.

Syntax validation is different from schema validation

JSON requires double-quoted strings and property names. Comments and trailing commas are not valid JSON. A valid top-level value can be an object, array, string, number, boolean or null.

The formatter validates the syntax, then indents the original tokens rather than serializing a parsed object back into new numeric text. It deliberately preserves duplicate keys, which are a portability concern: different consumers may retain only the last occurrence.

Object: {"key": value}
Array: [value, value]
String escapes include \" and \\ and \n
Numbers do not allow NaN or Infinity literals.

Input limits and common mistakes

The input limit is 200,000 characters, nesting is limited to 64 levels, and formatted output is bounded. Syntax errors are reported rather than repaired automatically. No code is evaluated.

Valid syntax does not establish that a document matches your application’s schema, has unique keys or contains correct data. Text is rendered as text, not as executable HTML. Copying a formatted document into another application still requires trusting that application.

Questions about json formatter and validator

Sources and verification

These references explain the formulas or formats. The worked examples above were created for this tool and checked against independent calculations or format round trips. AI-assisted development does not imply a named human expert review.

• MDN: JSON.parse syntax and errors — JSON grammar, double quotes and invalid trailing commas.

Published 2026-10-23. Examples are illustrations, not measurements of a service or claims about search rankings.

Related tools