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.
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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 to make it human-readable during development and debugging.
Common JSON Syntax Errors
The most frequent JSON mistakes are: trailing commas after the last array element or object property (valid in JavaScript but not JSON), single quotes instead of double quotes for strings and keys, unquoted keys (JSON requires all keys to be strings in double quotes), and comments (JSON does not support comments — use JSONC format if you need them).
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). 4-space is common in Python projects and some style guides. The choice is purely aesthetic — pick whichever matches your project's existing style.