JSON Formatter
Format, validate and minify JSON documents
Online JSON Formatter and Validator - Beautify and Minify
What is JSON and why does it matter so much in web development?
JSON (JavaScript Object Notation) is the most widely used data interchange format in modern web development and APIs. Its lightweight syntax, readable by humans and trivial for machines to parse, makes it ideal for communication between frontend and backend through REST and GraphQL APIs, configuration files such as package.json and tsconfig.json, data storage in NoSQL databases like MongoDB and Firebase, browser storage through localStorage, and real-time data over WebSockets. JSON supports primitive types (strings, numbers, booleans, null) plus arrays and nested objects.
What does this online JSON formatter and validator do?
This free tool covers the tasks you need when working with JSON: beautifying minified JSON so it becomes readable with configurable indentation (2 or 4 spaces, or tabs), validating the syntax and pinpointing errors such as missing commas, wrong quotes or unclosed structures, minifying JSON by stripping spaces, tabs and line breaks to reduce API transfer size, and displaying the hierarchical structure of complex data in a clear, navigable way.
The most common JSON syntax errors and how to fix them
The mistakes this tool helps you catch are the ones that show up most often: trailing commas after the last element of an array or object, which standard JSON does not allow; single quotes instead of double quotes, since JSON accepts double quotes only; unquoted or single-quoted property names; comments, which JSON does not support unlike JSONC; undefined values or JavaScript functions; unescaped control characters inside strings; and unbalanced structures with braces or brackets left open.
If you work with this tool, you will probably also find these useful JSON to CSV, CSV to JSON, Text Escaper, YAML/JSON Converter.
Frequently asked questions
Why does JSON not allow trailing commas?
Unlike JavaScript and other languages that tolerate them, the JSON specification (RFC 8259) is strict and does not allow a trailing comma after the last element. That decision keeps parsing simple and removes ambiguity. If your JSON contains trailing commas most parsers will reject it with "Unexpected token" or a JSON.parse error. Some editors and tools use JSONC (JSON with Comments), which is more permissive, but that is not standard JSON.
Can I put comments in a JSON file?
No, the official JSON standard supports no comments at all, neither // nor /* */. For configuration files that need documentation you have alternatives: JSON5 (a more flexible extension of JSON), JSONC (JSON with Comments, used by VS Code), YAML (which supports # comments), or keeping the documentation in a separate file. Tools such as TypeScript and VS Code process .jsonc files where comments are allowed.
Is there a size limit for a JSON file?
The JSON specification defines no theoretical size limit, but practical implementations do. Browsers typically handle 500 MB to 1 GB before memory problems appear. Node.js has configurable limits. APIs usually cap requests somewhere between 1 MB and 100 MB. For very large datasets consider streaming JSON (processing it in chunks), paginating your API, binary formats such as Protocol Buffers or MessagePack, or a purpose-built database.