JSON Formatter & Validator Online Free

JSON Formatter

Beautify, minify, and validate JSON data. Syntax highlighting and error detection.

100% private - everything runs in your browser, no data is sent anywhere

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JSON Formatter, Validator and Minifier for Developers

JSON (JavaScript Object Notation) is the most widely used data interchange format in modern web development. It is used by APIs, configuration files, databases, and applications worldwide. Working with minified or poorly formatted JSON is frustrating - our formatter instantly beautifies JSON with proper indentation, validates the structure, and highlights errors.

Valid JSON follows strict syntax rules - keys must be in double quotes, strings must be in double quotes (not single quotes), numbers cannot have leading zeros, and no trailing commas are allowed. Our validator catches all these errors instantly.

Common JSON Use Cases

  • REST API responses - debugging payloads from backend services
  • Configuration files - package.json, tsconfig.json, .eslintrc.json
  • Database documents - MongoDB, Firestore, DynamoDB, CouchDB
  • Webhook payloads - payment gateways, messaging APIs, CI/CD pipelines
  • Mobile and web app data exchange between frontend and backend
  • Government and enterprise APIs that return structured data

Common JSON Syntax Errors and How to Fix Them

Most JSON parse errors come from a handful of mistakes. Here are the ones developers run into most often:

  • Trailing commas - JSON does not allow a comma after the last item in an array or object. JavaScript does, which is why this mistake is so common when copying data between the two.
  • Single quotes instead of double quotes - all keys and string values must use double quotes. Single quotes and backticks are not valid JSON.
  • Unescaped special characters - newlines, tabs, and backslashes inside strings must be escaped (\n, \t, \\). Pasting multi-line text directly into a JSON string will break the parser.
  • Comments - standard JSON does not support // or /* */ comments. Remove them before parsing. JSONC (used by VS Code, TypeScript config) allows comments, but strict JSON parsers will reject them.
  • Unquoted keys - every key must be wrapped in double quotes. {name: "test"} is valid JavaScript but invalid JSON.
  • Numbers with leading zeros - 007 is not valid JSON. Use 7 instead. This catches people working with IDs or codes that happen to start with zero.

JSON Formatter vs JSON Validator - What is the Difference?

A JSON formatter (also called a beautifier or pretty-printer) takes valid JSON and adds whitespace, indentation, and line breaks to make it human-readable. A JSON validator checks whether the input conforms to the JSON specification and reports exactly where errors are.

This tool does both. When you paste JSON, it validates the structure first. If valid, it formats the output with proper indentation. If invalid, it highlights the exact line and character where the error occurs so you can fix it immediately.

Minification is the reverse of formatting - it strips all whitespace to produce the smallest possible output. Use minification when you need to reduce payload size for API responses, store compact data, or prepare JSON for transmission over a network.

Frequently Asked Questions

How does the JSON formatter work?+
Paste or type your JSON data and the tool instantly beautifies, minifies, or validates it with syntax highlighting and error detection. All processing happens in your browser - your data is never sent to a server.
Why does my JSON have a trailing comma error?+
JSON does not allow trailing commas after the last item in an array or object. For example, {"name": "test",} is invalid. Remove the comma after the last value to fix it. This is one of the most common JSON errors because JavaScript allows trailing commas but JSON does not.
Why does JSON require double quotes instead of single quotes?+
The JSON specification (RFC 8259) requires all keys and string values to use double quotes. Single quotes, backticks, and unquoted keys are not valid JSON even though they work in JavaScript. Our validator flags this immediately.
How do I escape special characters in JSON?+
Use a backslash to escape special characters: \" for double quotes, \\ for backslashes, \n for newlines, \t for tabs. Unescaped control characters inside strings are a common source of parsing errors, especially when copying text from other sources.
What is the difference between JSON formatter and JSON validator?+
A formatter (or beautifier) adds indentation and line breaks to make JSON readable. A validator checks whether the JSON is structurally correct according to the specification. This tool does both - it formats your JSON and highlights any syntax errors it finds.
When should I minify JSON instead of beautifying it?+
Minify JSON when you need to reduce payload size for API responses, configuration files, or network transfers. Beautify when you need to read, debug, or edit the data. Minified JSON removes all whitespace and newlines, which can reduce file size significantly.
Why am I getting a JSON parse error from an API response?+
Common causes include: the response is not actually JSON (check Content-Type header), the response contains a BOM (byte order mark) at the start, there are unescaped characters in string values, or the server returned an HTML error page instead of JSON. Paste the response into this tool to see exactly where the error is.
Why am I getting 'Unexpected token < in JSON at position 0'?+
Your code called JSON.parse() on a response that starts with '<' - which means the server returned HTML (usually an error page like <!DOCTYPE html>) instead of JSON. Check the response Content-Type header (should be application/json), verify the API URL is correct, and confirm the endpoint is up. Other common variants: 'Unexpected token u' means the input is the string 'undefined'; 'Unexpected token o' means you passed an object instead of a string. See our common JSON errors guide for the full list with fixes.
Can JSON contain comments?+
No. Standard JSON does not support comments. If you see // or /* */ comments in a JSON-like file, it is likely JSONC (JSON with Comments) used by tools like VS Code settings or tsconfig.json. Remove all comments before using the data as standard JSON.