Free Web Tools
JSON Formatter & Validator
Format, validate, minify, and repair JSON instantly. Live validation as you type,
syntax highlighting, sort keys, file upload, and auto-fix for trailing commas,
single quotes & unquoted keys. 100% free.
Syntax Highlighting
Live Validation
Format & Minify
Repair JSON
Sort Keys
File Upload
What Is JSON?
JSON (JavaScript Object Notation) is a lightweight, text-based data format used to exchange information between applications. It represents data as key-value pairs (objects) and ordered lists (arrays), and supports strings, numbers, booleans, null, objects, and arrays as value types. Despite its name, JSON is completely language-independent and is supported by virtually every programming language.
JSON is the dominant format for web APIs, configuration files, database documents (MongoDB, Firestore), and data serialization. If you work in web development, you encounter JSON every day.
Why Format JSON?
Raw JSON from an API or a log file is often delivered as a single compressed line — impossible to read at a glance. Formatting (or "pretty-printing") adds indentation and newlines so you can see the structure clearly: which keys belong to which object, how deep an array is nested, and where a value is located. This tool formats JSON with 2-space, 4-space, or tab indentation.
/* Minified (hard to read) */
{"user":{"name":"Alice","age":30,"roles":["admin","editor"]}}
/* Formatted (easy to read) */
{
"user": {
"name": "Alice",
"age": 30,
"roles": ["admin", "editor"]
}
}
Common JSON Errors and How to Fix Them
Trailing comma
{"a": 1, "b": 2,} — the comma after the last item is invalid JSON. The Repair button removes these automatically.
Single quotes
{'key': 'value'} — JSON requires double quotes. Single quotes are valid JavaScript but not valid JSON. Repair converts them.
Unquoted keys
{key: "value"} — keys must be quoted strings in JSON. This is valid JavaScript object syntax but not JSON. Repair adds the missing quotes.
Comments
// comment and /* block */ comments are not part of the JSON spec. Repair strips them before parsing.
Undefined / NaN
JavaScript values like undefined, NaN, and Infinity are not valid JSON. Replace them with null or a numeric alternative.
JSON vs JSONC vs JSON5
JSON
The strict standard (RFC 8259). No comments, no trailing commas, double quotes only. Used for APIs, data storage, and interoperability.
JSONC
JSON with Comments — used by VS Code for settings.json, tsconfig.json, etc. Adds // and /* */ comments. Not parseable by standard JSON parsers.
JSON5
Superset of JSON that adds unquoted keys, single quotes, trailing commas, and comments. Useful for hand-written config files. Requires a JSON5 parser library.
Frequently Asked Questions
How do I validate JSON in JavaScript?
Use a try/catch around JSON.parse(): if it throws, the JSON is invalid. The error object includes a message with position information in most browsers. This tool uses the same approach to give you line and column numbers when validation fails.
What is the maximum size of a JSON file?
There is no theoretical limit in the JSON specification. In practice, browser-based tools (like this one) are limited by available JavaScript heap memory. For files larger than a few MB, use a server-side parser (PHP's json_decode(), Python's json.loads(), or Node.js's JSON.parse()) which handles larger inputs more efficiently.
Does JSON support dates?
No. JSON has no native date type. Dates are typically represented as ISO 8601 strings (e.g. "2025-01-15T09:30:00Z") or as Unix timestamps (integers). When parsing, your application code must convert these strings to Date objects.
Is JSON better than XML?
For most modern use cases, yes. JSON is more compact, faster to parse, and maps naturally to data structures in JavaScript, Python, and most other languages. XML has advantages for document-centric data (mixed content, namespaces, attributes vs. elements) and is still common in SOAP APIs and some enterprise systems. For REST APIs and configuration, JSON is the clear standard today.
