JSON Formatter & Validator

Frequently Asked Questions

What is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format that is easy for humans to read and write, and easy for machines to parse and generate. Created by Douglas Crockford in the early 2000s, JSON uses key-value pairs and ordered lists: {"name": "John", "age": 30, "cities": ["NYC", "LA"]}. It has become the de facto standard for web APIs, replacing XML in most modern applications.

What is the difference between JSON and a JavaScript object?

While JSON syntax is derived from JavaScript objects, there are important differences. JSON requires double quotes around all keys and string values (not single quotes). JSON cannot contain functions, undefined values, comments, or trailing commas. JavaScript objects are more flexible and can include any valid JavaScript. Use JSON.parse() to convert a JSON string to a JavaScript object, and JSON.stringify() to convert an object to JSON.

Can JSON have comments?

No, standard JSON does not support comments. This is by design—JSON is meant to be a pure data format. If you need comments, consider using JSON5 (an extension that allows comments), JSONC (JSON with Comments, used by VS Code), or YAML which supports comments natively. Another approach is to use a "_comment" key in your JSON objects, though this becomes part of the data.

What are the valid data types in JSON?

JSON supports six data types: strings (text in double quotes), numbers (integers or floating-point, no quotes), booleans (true or false, lowercase), null (represents empty/no value), arrays (ordered lists in square brackets), and objects (key-value pairs in curly braces). JSON does not support undefined, functions, dates (use ISO 8601 strings), or binary data (use Base64 encoding).

How do I validate JSON?

Valid JSON requires: double quotes around all keys and strings, no trailing commas after the last element, no comments, proper nesting of brackets and braces, and values must be one of the six valid types. Our formatter validates JSON in real-time and highlights errors with line numbers. Common validation errors include missing quotes, trailing commas, and using single quotes instead of double quotes.

What is the maximum size of a JSON file?

JSON itself has no size limit—it is just a text format. However, practical limits depend on the parser and system. JavaScript can handle JSON files up to several hundred megabytes. Most APIs limit request/response size (commonly 1-10 MB). For very large datasets, consider JSON Lines (JSONL) format, streaming parsers, or binary formats like Protocol Buffers or MessagePack.

How do I validate JSON in code?

In JavaScript: wrap JSON.parse() in a try-catch block. In Python: use json.loads() with try-except. In PHP: use json_decode() and check json_last_error(). Most languages throw an exception or return an error for invalid JSON. For schema validation (checking structure, not just syntax), use libraries like Ajv (JavaScript), jsonschema (Python), or JSON Schema validators in other languages.

What is JSON Schema?

JSON Schema is a vocabulary for defining the structure, constraints, and documentation of JSON data. It specifies required properties, data types, value ranges, string patterns, and nested structures. Example: {"type": "object", "required": ["name"], "properties": {"name": {"type": "string"}, "age": {"type": "integer", "minimum": 0}}}. JSON Schema is used for API validation, form generation, and documentation.

How is JSON different from XML?

JSON is more compact and easier to read than XML. JSON uses {"name": "John"} while XML uses <name>John</name>. JSON parses directly to native data structures; XML requires DOM parsing. JSON has built-in arrays; XML requires workarounds. XML supports comments, namespaces, and attributes; JSON does not. JSON is preferred for APIs and configuration; XML is still used for document markup and legacy systems.

What are common JSON syntax errors?

The most common JSON errors are: using single quotes instead of double quotes, forgetting quotes around keys, trailing commas after the last array/object element, including comments (// or /* */), using undefined or NaN, unescaped special characters in strings, and mismatched brackets or braces. Our formatter detects all these errors and shows the error location.

Complete Guide to JSON

Related Tools