What is JSON Formatter?
Free JSON formatter and validator. Paste messy JSON to instantly format, validate, and highlight errors. Supports minify, indent options, and copy. No signup required.
JSON Formatter runs entirely in your browser using JavaScript (browser). Your data never leaves your device.
Free JSON Formatter
Paste any JSON string to instantly format it with proper indentation, validate its syntax, and highlight errors with line numbers. Minify JSON for production or pretty-print for readability. Choose 2-space or 4-space indentation. Works with any valid JSON including nested objects, arrays, and Unicode. 100% browser-based.
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Validates instantly
Syntax errors are shown immediately with the position of the problem.
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Syntax highlighting
Keys, strings, numbers, booleans, and null are colour-coded for easy scanning.
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100% private
Your JSON is processed in your browser and never sent to a server.
Frequently Asked Questions
What does JSON formatting do?+
JSON formatting (also called pretty-printing or beautifying) adds consistent indentation and line breaks to make JSON readable. Minifying removes all unnecessary whitespace to reduce file size for production use.
What causes a JSON validation error?+
Common causes: trailing commas after the last item, single quotes instead of double quotes, unquoted keys, missing commas between items, or unclosed brackets. The error message will indicate the position of the problem.
Is my JSON data safe?+
Yes. All formatting happens in your browser using JavaScript. Your JSON is never sent to any server, making it safe for API keys, tokens, and sensitive data.
What is the difference between format and minify?+
Format adds indentation and line breaks for human readability. Minify removes all whitespace, producing the smallest possible JSON string — typically 20-40% smaller. Use minified JSON in production API responses and source files, formatted JSON when debugging.
Can I format very large JSON files?+
Yes, within browser memory limits. Files up to ~50 MB process fine on modern devices. For files larger than that, a dedicated desktop tool may be faster.
What is the difference between JSON and JavaScript object literal syntax?+
JSON is a strict subset of JavaScript, but with tighter rules: all keys must be double-quoted strings, no trailing commas are allowed, no comments, no undefined values, and no functions. A valid JavaScript object literal (e.g., {key: 'value'}) is not valid JSON — the key must be "key" and the string must use double quotes.
Can I use JSON formatter to validate API responses?+
Yes. Copy any raw API response and paste it into the formatter. If it contains a syntax error, the validator highlights the line and describes the problem. This is faster than reading raw minified JSON from browser developer tools and is useful for debugging third-party API integrations.
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JSON Formatting and Validation Explained
JSON (JavaScript Object Notation) is the most widely used data format for APIs, configuration files, and data storage. Minified JSON removes all whitespace to reduce payload size — a 10 KB JSON file can often be reduced to 7 KB minified. Formatted JSON adds indentation and line breaks to make it human-readable during development and debugging. This tool validates JSON syntax at the same time, so any errors are caught and reported before you use the data.
Common JSON Syntax Errors and How to Fix Them
The most frequent JSON mistakes are: trailing commas after the last array element or object property (valid in JavaScript but illegal in strict JSON), single quotes instead of double quotes for strings and keys, unquoted keys (all JSON keys must be double-quoted strings), and comments (JSON does not support // or /* */ — use JSONC format or strip comments before validating). The validator shows the line number and character position of any error, so you can jump straight to the problem.
When to Use 2-space vs 4-space Indentation
2-space indentation is the standard in most JavaScript and TypeScript projects (enforced by Prettier defaults and the Airbnb style guide). 4-space is common in Python projects and some legacy style guides. The choice is purely aesthetic — pick whichever matches your project's existing conventions. Both options produce fully valid, identical JSON; indentation is stripped by any JSON parser.
JSON vs JavaScript Object Literals
JSON looks similar to JavaScript object syntax but follows stricter rules. In JSON: all keys must be double-quoted strings; string values must use double quotes (not single); trailing commas after the last item are not allowed; undefined is not a valid value; functions, dates, and NaN are not supported. A JavaScript object literal like { key: 'value' } is not valid JSON — but converting it is simple: wrap keys in double quotes and switch to double-quote strings.
Using JSON Formatter for API Debugging
When debugging an API, copy the raw response body from your browser's Network tab or from a tool like Postman and paste it here. The formatter pretty-prints nested objects and arrays instantly, making it easy to navigate deep response structures. The validator catches any malformed responses that might silently fail in your application. For large API responses with hundreds of nested keys, formatted JSON with 2-space indentation is significantly easier to scan than minified output.