JSON Formatter & Validator
Format, validate, minify and visualize JSON. Syntax highlighting, tree view, download. 100% in your browser.
Paste
Paste or upload your JSON
Format
Format, minify or view as tree
Use
Copy or download the result
JSON Format Guide: Everything You Need to Know
When to Use JSON
JSON is the most widely used data format in modern web development. You'll find it in REST API responses, configuration files (package.json, tsconfig.json, .eslintrc), NoSQL databases like MongoDB and CouchDB, and data exchange between microservices. If you're working with structured data on the web, JSON is almost always the right choice.
The 5 Most Common JSON Errors
Even experienced developers make these mistakes. Here are the most frequent ones and how to fix them:
- Trailing comma —
{"a":1, "b":2,}is not valid. Remove the comma after the last element. - Single quotes —
{'name': 'John'}is not valid JSON. Always use double quotes:"name". - Comments — JSON does not support comments (
// noteor/* block */). Use JSONC or JSON5 if you need them. - Non-standard values —
NaN,Infinity,undefined, and functions are not valid JSON values. - Wrong encoding — JSON must be UTF-8. Special characters need escaping:
\nfor newlines,\"for double quotes inside strings.
JSON vs XML: Which One to Choose
JSON is more compact, readable, and faster to parse than XML. A JSON object with 3 fields weighs about 30-40% less than the same data in XML. JSON is native to JavaScript and supported by every modern programming language. XML remains preferable when you need namespaces, strict schemas (XSD), or XSLT transformations, typically in enterprise and SOAP contexts.
Format vs Minify: When to Do What
Use formatting (pretty print) during development and debugging: it makes JSON readable with indentation and line breaks. Use minification in production: it removes spaces, tabs, and newlines to reduce file size. On a 100 KB JSON file, minification can save 20-40 KB — significant when you multiply by thousands of API requests per day.
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What is JSON format?
JSON (JavaScript Object Notation) is a lightweight, human-readable data interchange format. It is the de facto standard for web APIs, configuration files, and data exchange between applications. It supports strings, numbers, booleans, null, arrays, and objects.
How does JSON formatting work?
Formatting (or "pretty print") adds indentation and line breaks to compact JSON to make it readable. This tool uses standard 2 or 4 space indentation. Minification does the opposite: removes all unnecessary whitespace to reduce file size.
Is my JSON data safe?
Yes, completely. All parsing and formatting happens in your browser using native JSON.parse() and JSON.stringify(). No data is ever sent to external servers.
What is the difference between valid and invalid JSON?
Valid JSON must follow strict rules: keys must be double-quoted strings, no trailing commas, no comments, no undefined values. Common errors include: single quotes instead of double, comma after the last element, NaN or Infinity as values.
Can I format large JSON files?
Yes, the tool handles JSON files up to several MB directly in the browser. For very large files (>10MB), performance depends on your device. Processing is entirely local, so there are no upload limits.
What is the difference between JSON, JSONC, and JSON5?
JSON is the strict standard: no comments, double quotes only, no trailing commas. JSONC (JSON with Comments) allows // and /* */ comments — used by VS Code for its configuration files. JSON5 is even more permissive: it supports single quotes, unquoted keys, trailing commas, and comments. This tool validates against the strict JSON standard, which is the most universally compatible.
How do I find errors in my JSON?
Paste your JSON and select the "Validate" mode. The tool analyzes the structure and shows the error type (missing comma, wrong quotes, invalid value) with the exact line and position. This lets you fix the problem in seconds instead of searching through hundreds of lines by eye.
What is the tree view for?
The tree view transforms JSON into a navigable structure with expandable nodes. It's particularly useful for complex JSON with many nesting levels: you can open only the sections you're interested in, see the type of each value, and count array elements without reading all the code.
How much file size do I save by minifying JSON?
It depends on the structure, but typically minification reduces size by 20-40%. A 100 KB formatted JSON becomes roughly 60-80 KB when minified. The difference is larger for JSON with many nesting levels and long keys. For high-traffic APIs, this saving multiplied by thousands of requests makes a significant difference in bandwidth and transfer times.
Can I use this tool to validate API responses?
Yes, it's one of the most common use cases. Copy the JSON response from your browser console (DevTools → Network → Response) and paste it here. The tool will format it to make it readable, validate the structure, and show statistics (number of keys, depth, size). It's perfect for debugging endpoints that return malformed or unexpected JSON.
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