Free JSON Formatter and Validator Online

How to format JSON online

1. Paste your JSON string into the input field. It can be minified, partially formatted, or hand-written.
2. Click Format to parse and output indented JSON with 2-space indentation per level.
3. If the JSON has a syntax error, the tool shows the error message and character position instead of output.
4. Click Minify to strip all whitespace and produce the most compact valid JSON string.
5. Use the Copy button to copy the formatted or minified result to your clipboard in one click.

JSON beautifier: reading API responses and nested structures

API responses are almost always returned as minified JSON to reduce payload size. A response with hundreds of keys and deep nesting is unreadable as a single line. The JSON beautifier parses the raw string and outputs it with one key-value pair per line and indentation that reflects nesting depth. This makes it immediately obvious where objects start and end, which keys belong to which object, and how many levels deep a value sits.

JSON pretty print is particularly useful when debugging REST API integrations, webhook payloads, and GraphQL responses. Copy the raw response body from your browser's network tab or from a tool like Postman or curl, paste it here, format it, and navigate the structure visually. For JWT token inspection alongside JSON formatting, the Base64 decoder decodes the JWT payload section so you can then inspect its JSON claims in this formatter.

JSON validator and syntax checker

The JSON validator parses your input against the RFC 8259 specification, which is stricter than JavaScript object literal syntax in several ways. It rejects trailing commas after the last item in an array or object, which JavaScript engines accept. It requires all strings and all object keys to use double quotes, while JavaScript allows single quotes and unquoted keys. It does not permit comments of any kind, while some configuration file formats like JSON5 or JSONC do allow them.

When validation fails, the error message includes the character position (index in the string) where the parser encountered an unexpected token. For large JSON documents, count from the start of the string or use the position to navigate directly to the fault. Common fixes: replace single quotes with double quotes, remove trailing commas, add missing commas between items, close any unclosed brackets or braces, and escape special characters inside strings using \" for quotes and \\ for backslashes.

JSON minifier: compressing JSON for production

The JSON minifier removes all whitespace that appears outside of string values: spaces, tabs, and newlines used only for human readability. The resulting minified JSON is the most compact valid representation of the same data. For API responses, minified JSON reduces payload size by 15 to 40 percent compared to formatted JSON, which translates directly to faster transfer times and lower bandwidth costs at scale.

Common use cases for the JSON compressor are preparing static JSON files for embedding in web pages, reducing the size of configuration files bundled into applications, and generating test fixtures that need to fit within size limits. In JavaScript, JSON.stringify(data) without the third argument produces minified output. In Python, json.dumps(data, separators=(',', ':')) achieves the same result. This tool minifies any JSON in one click without writing code.

JSON in API development and debugging

JSON is the dominant data format for web APIs. REST APIs, GraphQL responses, webhook payloads, OAuth token responses, and most configuration file formats use JSON. During development and debugging, you regularly encounter JSON in contexts where it is not already formatted: terminal output from curl, raw logs, database column values, clipboard copies from browser devtools, and strings embedded in error messages.

This online JSON formatter handles all of these cases. Paste the raw string directly, including surrounding characters that are not part of the JSON (the validator will identify where the JSON boundaries are). For API responses that use URL percent-encoding in values alongside JSON structure, the URL encoder and decoder handles the percent-encoding layer separately. For API responses that include SHA hashes of resource content, the SHA hash generator verifies hash values. For responses containing UUID identifiers in JSON fields, the UUID generator produces new UUIDs in the same format for test data.

JSON data types and structure rules

JSON supports six data types: strings (in double quotes), numbers (integers and floats, no quotes), booleans (true and false, lowercase only), null (null, lowercase only), objects (key-value pairs in curly braces, keys always double-quoted), and arrays (ordered lists in square brackets). These types can nest arbitrarily deep. A JSON document must have exactly one root value, which can be any of the six types including a bare string, number, or array.

Numbers in JSON have no distinction between integer and float types in the specification itself, but parsers in different languages may interpret them differently. Very large integers beyond the safe integer range of JavaScript (above 2^53 - 1) should be represented as strings to avoid precision loss. Dates have no native JSON type and are conventionally represented as ISO 8601 strings. Binary data is typically Base64-encoded into a JSON string field rather than embedded directly.

How the JSON formatter works in the browser

The formatter uses the browser's native JSON.parse() function to parse the input into a JavaScript object or array. If parsing succeeds, it passes the result to JSON.stringify(value, null, 2) for formatted output or JSON.stringify(value) for minified output. If parsing throws a SyntaxError, the error message from the engine (which includes the character position) is displayed directly.

Everything runs client-side. No network request is made. Your JSON data never leaves your device, which makes this safe for pasting API keys, tokens, internal schemas, and any sensitive structured data you need to inspect or reformat. The tool has no memory between sessions. Closing or refreshing the page clears all input.