JSON formatter & validator
Make a JSON response easier to read or check why a configuration will not parse. Formatting happens in this page, with no API request.
JSON formatter & validator
Runs on your deviceJSON is a data format with specific rules
Object keys and string values use double quotation marks. Numbers, true, false, and null are not quoted unless you intend them to be strings. Comments, trailing commas, single-quoted strings, and JavaScript expressions are not accepted JSON. The formatter uses the browser’s JSON parser and reports its error rather than executing the input as code.
Formatting changes representation
Pretty printing adds indentation and line breaks without intentionally changing the parsed data. Compact mode removes unnecessary whitespace. Parsing and writing can still change how numbers and escape sequences are represented. Duplicate object keys collapse to the last value when parsed. JavaScript numbers also have precision limits, so represent identifiers and very large integers as strings if their exact digits matter.
Validation is not a schema check
A JSON document can be syntactically valid and still be wrong for an application. For example, a score stored as a string may parse successfully even when your API expects a number. This tool checks syntax only. It does not validate a JSON Schema, resolve links, contact an API, or recover lost duplicate keys. The input limit is one million characters; keep the original when editing a sensitive configuration.
Worked examples
| Input | Mode | Result |
|---|---|---|
| {"a":1,"b":2} | Pretty print | The same object, indented |
| {a: 1} | Any mode | A syntax error: the key needs double quotes |
Good questions.
Does valid JSON mean the API will accept it?
No. An API can require specific fields, types, or permissions in addition to valid JSON syntax.
Can I paste JavaScript?
Only the JSON subset is accepted. The tool does not execute JavaScript.
Are large integers preserved?
Not always. The browser parser uses JavaScript numbers. Keep exact large identifiers in quoted strings.
References & further reading
Updated 5 November 2026 · Methods & corrections