JSON Formatter & Validator

JSON (JavaScript Object Notation) is a lightweight, language-agnostic text format for data interchange defined by RFC 8259 and ECMA-404. Our validator strictly adheres to RFC 8259 specifications, validating structural tokens ({, }, [, ], :, ,), string encoding with UTF-8 escape sequences, numeric formats (including scientific notation), and boolean/null literals. Any deviations such as unquoted keys or trailing commas are flagged with exact line and column coordinates.

The Auto-Repair engine scans your malformed JSON for common non-standard syntax patterns and repairs them without altering your core data. It strips single-line (//) and multi-line (/* */) comments, converts Python literals (True, False, None) into standard JSON (true, false, null), removes illegal trailing commas before closing brackets and braces, converts single-quoted strings into valid escaped double-quoted strings, and wraps unquoted property names in double quotes.

Yes, 100% safe. This tool executes entirely client-side within your browser's local JavaScript V8/Webkit engine. Your JSON data is never transmitted across the network, never logged, and never stored on any server. You can safely inspect private production payloads, Bearer tokens, environment variables, and confidential customer datasets without any privacy or compliance risks.

Yes! Switch to the 'TypeScript Interfaces' tab to instantly inspect auto-inferred TypeScript type definitions and interfaces based on your JSON structure. The generator recursively traverses all nested objects and arrays, creating clean, strongly-typed interfaces in PascalCase with proper primitive mappings (string, number, boolean, null, or custom sub-interfaces). You can copy the code or download it directly as a .d.ts declaration file.

According to the JSON specification (RFC 8259), commas are strictly defined as delimiters between collection elements, not terminators. Therefore, a comma immediately preceding a closing brace (}) or bracket (]) is a syntax violation. Similarly, RFC 8259 explicitly mandates that strings must begin and end with double quotation marks ("). While relaxed supersets like JSON5 or JavaScript allow single quotes and trailing commas, standard parsers in Python, Java, Go, and C# will throw exceptions if they encounter them.

In JavaScript/Node.js, use JSON.stringify(data, null, 2) where the third argument specifies the number of spaces for indentation. In Python, use json.dumps(data, indent=2) or run the command-line utility: python -m json.tool input.json. In Linux/macOS terminals with curl, you can pipe responses directly into jq: curl https://api.example.com | jq .

Pretty-printing adds human-readable formatting, newlines, and uniform indentation (typically 2 or 4 spaces) to make hierarchical structures easy to inspect and debug. Minification strips out all non-essential whitespace, line breaks, and indentation tabs, reducing payload size by 20% to 40% to save bandwidth and decrease latency during HTTP API transfers and web socket transmissions.

Because processing runs entirely in your local browser memory, this tool comfortably handles JSON payloads up to 25MB–50MB (hundreds of thousands of lines) without performance degradation on modern devices. For massive files, you can use the file upload button or drag-and-drop feature to load files directly from disk without paste-buffer lag.