What Is JSON and Why Does Formatting Matter?

JSON (JavaScript Object Notation) is a lightweight, human-readable data interchange format. It is the de facto standard for REST API responses, configuration files, and data serialisation across virtually every programming language. Well-formatted JSON is easy to read and diff; minified JSON is smaller to transmit. This tool lets you switch between both in one click.

Common JSON Errors to Watch For

Trailing commas — {"a": 1,} is invalid JSON (valid in JS but not JSON spec).
Single quotes — JSON requires double quotes for both keys and string values.
Unquoted keys — {name: "value"} is JavaScript object literal syntax, not JSON.
Missing or extra brackets — A mismatched { or [ causes the entire document to fail parsing.
Comments — Standard JSON does not support // comments or /* block comments */.

Common Use Cases

API debugging — Raw API responses are often minified. Format them to inspect the structure.
Configuration files — package.json, tsconfig.json, and many other config files use JSON.
Data interchange — Validating a JSON payload before submitting it to an API endpoint.

Tips for Large JSON Files

For very large JSON files (megabytes+), browser-based tools can be slow. Consider splitting the file or using a CLI tool like jq for large-scale processing. For files under a few hundred kilobytes, this tool handles formatting instantly.

Why Format JSON Locally?

API responses often contain sensitive data — authentication tokens, user records, personal information. Pasting this into a server-backed formatter risks that data being logged. This tool uses JavaScript's native JSON.parse() and JSON.stringify() — no network request is ever made.

JSON in PHP

json_encode($array) — Converts a PHP array or object to a JSON string
json_encode($array, JSON_PRETTY_PRINT) — Adds indentation and newlines for readable output
json_decode($json, true) — Parses a JSON string into a PHP associative array (the true flag is key)
json_last_error() — Returns the last JSON encoding/decoding error code
json_last_error_msg() — Returns a human-readable error message for the last JSON error

Laravel's response()->json($data) helper automatically calls json_encode() and sets the Content-Type: application/json header. For incoming requests, $request->json()->all() or $request->input() handles JSON payloads transparently.

Privacy & How It Works

All formatting and validation uses JavaScript's native JSON.parse() and JSON.stringify(). No JSON data is ever transmitted to any server.

No server calls — Parsing and formatting run entirely in your browser.
Works offline — Once the page loads, no internet connection is needed.
GDPR-safe — Zero data collection, zero data transmission.

JSON Formatter & Validator — Pretty Print & Minify Online