JSON Formatter & Validator
Free online JSON formatter and validator with inline error hints, collapsible tree view and in-browser processing.
Privacy: all processing happens locally in your browser. Your input never leaves your device.
What is JSON Formatter & Validator?
JSON (JavaScript Object Notation) is the most common data interchange format — API debugging, config files and log analysis all rely on it. But API responses are often compressed into one unreadable line, and hand-written JSON easily fails to parse because of trailing commas or single quotes. This tool formats, beautifies and validates JSON in one click: when parsing fails it points out the exact line and column with a readable reason (such as "keys must use double quotes"), and the formatted result appears as a collapsible tree so deeply nested structures stay easy to explore. All parsing happens locally in your browser — your data is never uploaded to any server, so it is safe to paste API payloads containing sensitive information.
How to Use
- Paste JSON into the input area on the left (or drop a .json file, or click "Sample" to load demo data)
- The tool formats in real time and shows the result on the right; syntax errors are highlighted inline with a readable explanation
- Use the toolbar to switch indentation (2/4 spaces), copy the result, or download it as a .json file
- Press Ctrl+Enter to trigger formatting manually
FAQ
- Why does {"name":"json"} parse but {name:'json'} does not?
- The JSON standard requires keys and strings to use double quotes. In {name:'json'} the key has no quotes and the value uses single quotes — both are invalid. Fix it to {"name":"json"}.
- Does JSON support comments or trailing commas?
- Standard JSON supports neither // or /* */ comments nor a comma after the last element. Use JSON5 or JSONC if you need comments — this site also offers a JSON5 parser.
- Does formatting change my data?
- No. Formatting only adjusts whitespace and indentation; keys, values and their order stay unchanged.
- Will large files freeze the page?
- Inputs over 1MB are automatically processed in a background Web Worker thread so the page stays responsive; all computation happens locally.
- Is my JSON uploaded anywhere?
- No. All parsing and formatting runs locally in your browser — no network request ever carries your data.
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Last updated 2026-09-04