Is this JSON formatter safe to use with sensitive data?

Yes. All processing happens entirely in your browser using JavaScript. Your JSON data is never transmitted to any server, never stored, and never logged. Close the tab and it's gone.

What is the difference between JSON formatting and JSON minifying?

Formatting (pretty-printing) adds indentation and line breaks to make JSON human-readable. Minifying removes all unnecessary whitespace to produce the smallest possible file size for production use.

Why is my JSON invalid?

Common JSON errors: trailing commas after the last item in an object or array, single quotes instead of double quotes around keys and string values, unquoted keys, comments (JSON doesn't support comments), and using undefined or NaN (which are JavaScript values, not valid JSON).

JSON Formatter & Validator — Free, Private, In-Browser

Common JSON errors and how to fix them

Error pattern	Problem	Fix
{"key": "value",}	Trailing comma after last item	Remove the comma before the closing brace or bracket
{'key': 'value'}	Single quotes instead of double quotes	Replace all single quotes with double quotes around keys and string values
{key: "value"}	Unquoted key	Wrap the key in double quotes: {"key": "value"}
// comment	Comments not supported in JSON	Remove all comments — JSON has no comment syntax
undefined, NaN, Infinity	JavaScript-only values not valid in JSON	Replace with null or a valid number
{name: undefined}	undefined value	Use null or omit the key entirely
"date": 2024-01-01	Unquoted date string	Wrap in quotes: "date": "2024-01-01"

JSON data types

JSON supports exactly six data types:

{
  "string":  "hello world",
  "number":  42,
  "float":   3.14,
  "boolean": true,
  "null":    null,
  "array":   [1, 2, 3],
  "object":  {"key": "value"}
}

Privacy first: This tool processes everything locally in your browser. Sensitive API keys, tokens, user data, and credentials in your JSON never leave your device. Safe for internal and confidential data.

What each action does

Format (Pretty-print)

Adds consistent indentation and line breaks to make nested JSON human-readable. Choose 2 spaces, 4 spaces, or tabs as the indentation style. Also validates the JSON and reports any errors before formatting.

Minify

Removes all whitespace (spaces, tabs, newlines) that isn't inside a string value. Produces the smallest possible valid JSON string — useful for API payloads, config files shipped with applications, and any situation where file size matters.

Validate only

Checks whether the input is valid JSON without changing it. Reports the exact line and character position of any errors. Useful when you want to confirm correctness without reformatting.

Sort keys

Reformats the JSON with all object keys sorted alphabetically at every level. Useful for comparing two JSON objects, normalising output for version control, or making large objects easier to scan.

Frequently asked questions

Is this JSON formatter safe for sensitive data?

Yes. Processing happens entirely in your browser — your JSON is never sent to any server and is not stored or logged anywhere. You can safely paste API keys, tokens, passwords, and confidential data. Close the tab and no trace remains.

Why does JSON not allow trailing commas?

JSON was designed for strict machine-to-machine data exchange and follows a very conservative grammar. Trailing commas were deliberately excluded to keep parsers simple and predictable across all platforms. JavaScript itself does allow trailing commas in objects and arrays, but JSON (despite sharing the same syntax visually) is a separate, stricter format.

What is the difference between JSON and JavaScript objects?

JSON is a text format for data exchange, not code. Key differences: JSON requires double quotes around all keys and string values (JavaScript objects allow unquoted keys and single quotes). JSON has no undefined, NaN, Infinity, functions, or Date objects. JSON is a strict subset of what JavaScript can represent.

Can JSON have comments?

No. Standard JSON does not support comments of any kind. If you need a config file format that supports comments, consider JSONC (JSON with Comments — used by VS Code), JSON5, HJSON, or TOML. If your file has // or /* */ comments, remove them before parsing as JSON.

Does this formatter handle very large JSON files?

Yes, within browser memory limits. Files up to several megabytes process instantly. Very large JSON files (10MB+) may take a second or two to format due to browser rendering limits for large text areas. For files larger than ~50MB, a CLI tool like jq is more suitable.

JSON Formatter & Validator