JSON Formatter / Validator
Format, minify, and validate JSON data online. Pretty-print with configurable indentation and see detailed error positions for invalid JSON.
Examples
About JSON Formatter
JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write, and easy for machines to parse and generate. It is the standard format for REST APIs, configuration files, and data storage.
Format mode pretty-prints your JSON with proper indentation, making it easy to read and understand nested structures. Minify mode removes all whitespace to produce the smallest possible output, ideal for network transfer and storage. Validate mode checks if your JSON is well-formed and shows the exact error location if not.
All processing happens client-side in your browser using the native JSON.parse() and JSON.stringify() methods. No data is sent to any server.
How to Use This JSON Formatter
This free online JSON formatter and validator makes it easy to work with raw JSON data. Whether you are debugging an API response, cleaning up a configuration file, or preparing an Ethereum ABI, follow these steps:
- Paste your JSON into the input area on the left. You can paste any JSON string, including API responses, package.json files, or smart contract ABIs.
- Choose your action — click Format to pretty-print the JSON with proper indentation, or click Minify to compress it into a single line for production use.
- Check for errors — if the JSON is invalid, the tool highlights the exact line and character where the syntax error occurs, so you can fix it quickly.
- Copy the output using the copy button and paste it into your code editor, terminal, or API client.
Everything runs locally in your browser. Your data is never sent to a server, making this tool safe for sensitive configuration files and private keys.
Common Use Cases
- API debugging — Format messy API responses to quickly inspect nested objects, arrays, and field values.
- Configuration file formatting — Pretty-print package.json, tsconfig.json, or Docker Compose files for readability.
- Data validation — Verify that JSON payloads are syntactically correct before sending them to a backend or smart contract.
- Ethereum ABI formatting — Pretty-print smart contract ABIs to review function signatures, event definitions, and parameter types.
- Minification for production — Compress JSON to reduce payload size in APIs, webhooks, and on-chain metadata.
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Frequently Asked Questions
What is JSON and what is it used for?
JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy for humans to read and write, and easy for machines to parse and generate. It is the most common format for transmitting data in web APIs, configuration files, and blockchain ABIs.
How do I validate JSON online?
Paste your JSON into the input field and the tool will automatically check for syntax errors. If your JSON is invalid, you will see a detailed error message pointing to the exact location of the problem, such as a missing comma, unclosed bracket, or trailing comma.
What is the difference between JSON and XML?
JSON is more compact and easier to read than XML. JSON uses key-value pairs and arrays, while XML uses tags and attributes. JSON is natively supported in JavaScript and is the standard for modern REST APIs, whereas XML is more common in legacy SOAP services and enterprise systems.
What does pretty-print JSON mean?
Pretty-printing JSON adds indentation, line breaks, and spacing to make the data structure easy to read. Minified JSON removes all whitespace to reduce file size for transmission. This tool lets you switch between both formats instantly.
What are the most common JSON syntax errors?
The most frequent JSON errors include trailing commas after the last item in an array or object, using single quotes instead of double quotes, unescaped special characters in strings, and missing closing brackets or braces.
Can I use JSON for Ethereum smart contract ABIs?
Yes. Ethereum smart contract ABIs are defined in JSON format. You can use this formatter to pretty-print and validate ABI files before using them with ethers.js, viem, or web3.js to ensure they are correctly structured.
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