Free 100% In-Browser Tool

JSON Validator, Linter & Pretty Formatter

Validate JSON data, locate syntax error lines, and format with customizable indentation.

Quick Answer:Paste your JSON text. The tool checks RFC 8259 syntax, pinpoints any error lines, and formats the output with 2-space indentation.

Initializing tool...

Privacy First: 100% Client-Side Processing

Processed in your browser. Files are never uploaded.

How to Use the JSON Validator: Format, Lint & Syntax Error Checker

1Paste your raw JSON string into the editor.
2Check the real-time status banner for valid JSON confirmation or error line location.
3Inspect key count, root data type (Array or Object), and total byte size.
4Click 'Auto-Format' to clean up messy indentation into structured JSON.

JSON.parse(str) → Validates AST; JSON.stringify(obj, null, 2) → Formats Indentation

Validates data structures against official ECMAScript grammar specifications.

Input: {"status": "ok", "items": [1, 2, 3]}

Explanation: Properly formatted with double quotes around keys and strings; no trailing commas.

Result: Valid JSON (Object, 2 keys, 36 bytes)

Why does JSON require double quotes around object keys?▼

The official RFC 8259 specification mandates double quotes to prevent ambiguity with programming language keywords.

Can JSON contain comments?▼

Standard JSON does not support comments; use JSONC (JSON with Comments) if comments are required by your tooling.

What is the maximum file size for browser JSON validation?▼

This client-side validator can comfortably handle multi-megabyte JSON payloads with fast browser execution.

How are JSON syntax error lines pinpointed?▼

The parser reads the byte offset where syntax deviation occurred and counts preceding newline characters to report the exact line number.

JSON Construct	Valid Syntax Example	Common Invalid Mistake
String	"Hello World"	'Hello World' (Single quotes invalid)
Keys	{"id": 1}	{id: 1} (Unquoted keys invalid)
Array	[1, 2, 3]	[1, 2, 3,] (Trailing comma invalid)
Boolean	true / false	True / False (Must be lowercase)

•Validating REST API requests and webhook payloads before sending to backend services.
•Formatting configuration files like package.json, tsconfig.json, and manifest.json.

Last reviewed & updated: 2026-11-11

Free & Open Access

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