What is JSON and why does it need formatting?

JSON (JavaScript Object Notation) is a lightweight data-interchange format. Raw JSON from APIs or databases is often minified (all on one line) to save bandwidth. Formatting adds indentation and line breaks, making it human-readable for debugging, documentation, and code review.

What is the difference between formatting and minifying JSON?

Formatting (beautifying) adds indentation and newlines to make JSON easy to read. Minifying removes all unnecessary whitespace to produce the smallest possible file size. Use formatting for development/debugging and minifying for production to reduce payload size.

Why does my JSON show a syntax error?

Common JSON errors include: trailing commas after the last item in an array or object, single quotes instead of double quotes around strings, unquoted property keys, missing commas between items, and comments (JSON does not support comments). The error message will indicate the line and position of the problem.

What indent size should I use?

2 spaces is the most popular choice in JavaScript and web projects. 4 spaces is common in Python and many style guides. Tabs are preferred by some teams and are the default in some editors. All three are valid - choose what matches your team's coding standard.

Is my JSON sent to any server?

No. All parsing, formatting, and validation happens entirely in your browser using JavaScript's built-in JSON.parse() and JSON.stringify(). Your data never leaves your device.

Can this tool handle large JSON files?

Yes. Since processing is done in-browser, it handles JSON of any size your browser can hold in memory. For very large files (tens of MB), formatting may take a second, but there is no artificial size limit.

JSON Formatter & Validator

Format, beautify, and validate JSON online. Free JSON formatter with syntax error detection - pretty print or minify JSON.

🔒 Your text stays in your browser - nothing is sent to our servers

Indent:

JSON Input

Formatted JSON

How to Use

Three steps to get started

Paste your JSON

Paste or type your JSON into the input area. Errors will be highlighted immediately.

Choose format or minify

Click "Format / Beautify" to pretty-print your JSON with your chosen indent size, or "Minify" to compress it.

Copy the result

Click Copy to copy the formatted or minified JSON to your clipboard, ready to use.

About This Tool

JSON formatting and validation explained

JSON (JavaScript Object Notation) is a text format for structured data, specified identically by RFC 8259 and ECMA-404. It permits exactly six value types: object, array, string, number, boolean, and null. A formatter takes valid JSON and re-emits it with consistent indentation; a validator tells you why the parser rejected it. This tool does both, and the important consequence is that formatting a document is also a proof that it parses.

Validation runs through the browser's native JSON.parse() - the same engine your application uses - so anything accepted here is accepted by your Node.js server, and anything rejected here would have thrown there too. There is no lenient fallback mode, which is the point.

Why is my JSON invalid? The usual suspects

Nearly every parse failure is one of these, and most stem from assuming JSON is a subset of JavaScript literal syntax. It is stricter:

Trailing comma: {"a": 1,} is legal in modern JavaScript and illegal in JSON. The most common single cause.
Single quotes: {'a': 1} fails. JSON strings require double quotes, always.
Unquoted keys: {a: 1} fails. Object member names are strings, not bare identifiers.
Comments: // and /* */ are not part of the spec. Formats like JSONC and JSON5 add them; plain JSON does not.
Non-finite numbers: NaN, Infinity, and -Infinity have no JSON representation. Leading zeros and a bare .5 are rejected too - write 0.5.
Smart quotes: Copying from a document or chat client can substitute curly quotation marks that look correct but are different codepoints entirely.

Pretty-print or minify?

Both operations preserve the data and change only whitespace between tokens. Pretty-printing rebuilds the document via JSON.stringify() at your chosen indent - 2 spaces (the JavaScript and npm convention), 4 spaces (common in Python and Java codebases), or tabs. Minifying strips every optional space and newline, typically cutting 10–30% off an indented payload and giving you what belongs in an HTTP body, a database column, or an inline <script> block.

Two things formatting will quietly do to you: duplicate keys collapse to the last value (the spec leaves this undefined and JavaScript picks last-wins), and integers beyond Number.MAX_SAFE_INTEGER - snowflake IDs are the classic example - lose precision on round-trip, so keep those as strings.

Parsing and re-serialization both happen locally in your browser tab, so production API responses and customer records can be pasted here without crossing a network boundary.

FAQ

Frequently Asked Questions

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