JSON Formatter

JSON (JavaScript Object Notation) is a lightweight, language-agnostic data interchange format specified by RFC 8259. It supports six value types: strings (always double-quoted), numbers, booleans, null, arrays, and objects. That's it. There are no trailing commas, no comments, no unquoted keys, no single quotes, no undefined, no dates, and noBigInt.

Formatting, minifying, validating

This tool runs everything in your browser using the native JSON.parse() and JSON.stringify(), so nothing is uploaded. Formatting pretty-prints the value with the indent you choose; minifying strips all whitespace for smallest payload size (useful for embedding in URLs or config files); and validating just confirms the structure parses and surfaces the first syntax error with its character offset.

Common errors and what they mean

• Unexpected token ... usually means a trailing comma, a missing closing brace, or a smart quote instead of a regular ".
• Unexpected end of JSON input means the parser reached EOF mid-value — often a truncated response body.
• Duplicate keyisn't a JSON error per se — the spec allows it and the last value wins — but it usually indicates a bug upstream.

When strict JSON isn't enough

If you need comments and trailing commas in config files, look at JSON5, JSONC (used by VS Code), or TOML. For large/streaming payloads, consider NDJSON (one JSON value per line) which is much easier to parse incrementally.