Developer tool
JSON Formatter
Format and validate JSON in your browser. Paste minified or messy JSON and get clean, indented output — or a clear error message explaining exactly what is wrong.
Your data is processed entirely on your device and never sent anywhere.
Privacy & data handling
Browser processingThis tool processes your input locally in your browser. Nothing is uploaded to a server or sent to an external service.
Interactive tool
JSON Formatter
Overview
What does JSON Formatter do?
This tool does two things at once: it validates your JSON and, if it is valid, formats it with proper indentation.
Validation matters because JSON is unforgiving — a missing comma, a stray quote, or a trailing comma turns the whole document invalid. Instead of hunting for the problem by eye, paste the JSON and the tool tells you the error and where it occurred.
When the JSON is valid, the output is reformatted with two-space indentation, turning a wall of text into a readable hierarchy of nested objects and arrays. You can copy the formatted result with one click.
Under the hood
How does it work?
The tool passes your input through JSON.parse, the browser's built-in JSON parser. If the text is valid JSON, JSON.parse produces a JavaScript object; if not, it throws an error with a message describing what it found and where.
For valid input, the object is then serialized with JSON.stringify using a two-space indent. That step rebuilds the JSON in a canonical, readable form: consistent spacing, quoted keys, and nested indentation.
The entire process runs in the browser — no request is made to any server, so the data you paste stays on your device.
Key features
Features of JSON Formatter
Use cases
When should you use JSON Formatter?
Debugging API responses
Paste a minified response body to see its structure, find a missing field, or understand what an endpoint actually returns.
Cleaning up configuration files
Configuration files for tools and services are often minified. Format them to review and edit with confidence.
Validating before coding
Check that a sample payload is valid before building against it, so your parser doesn't fail on malformed data.
Preparing test fixtures
Format a valid response into a clean fixture you can reuse in tests and mock servers.
Step-by-step
How to use JSON Formatter
- Step 1
Paste your JSON into the editor.
- Step 2
The tool automatically formats and validates it.
- Step 3
Copy the formatted JSON or fix any errors shown.
Real example
Example
Minified JSON
{"name":"John","age":30,"active":true,"tags":["admin","editor"],"address":{"city":"Oslo","zip":1234}}Formatted JSON
{
"name": "John",
"age": 30,
"active": true,
"tags": [
"admin",
"editor"
],
"address": {
"city": "Oslo",
"zip": 1234
}
}Valid input is re-indented and re-serialized into this canonical form.
Technical information
How the details work
JSON has a small but strict grammar. Keys must be wrapped in double quotes (single quotes are not allowed). Strings must use double quotes, so escaping an internal quote requires a backslash. Trailing commas — legal in JavaScript arrays and objects — are invalid in JSON. Comments are not part of the format at all; JSON was deliberately designed without them, which is one reason it is so easy for machines to parse.
JSON supports exactly these value types: objects, arrays, strings, numbers, booleans, and null. Dates are not a type — they are stored as strings and parsed by the application. Numbers are plain decimal; leading zeros and hexadecimal notation are not valid JSON numbers.
A useful distinction: formatting and validation are different jobs. Validation asks “is this valid JSON?” Formatting asks “what does it look like indented?” This tool does both in one pass — it must validate before it can safely format, because only valid JSON can be re-serialized faithfully.
Privacy & security
Your data stays yours
Your JSON is parsed and formatted entirely in your browser. Nothing is uploaded, logged, or stored.
Local processing — files stay in your browser
- JSON.parse and JSON.stringify run locally — no network request carries your data.
- Nothing is retained after you close the tab.
- The formatted result is copied directly from your browser.
- Analytics only record the page visit.
Limitations
What this tool does not do
- Duplicate keys are not flagged — JSON.parse keeps the last value silently.
- Very large documents (10 MB+) can slow down the browser.
- This is a formatter/validator, not a schema validator — it cannot check structure against a specification.
- Comments or single quotes make the document invalid (that is the JSON spec, not a limitation of the tool).
Frequently asked questions
Common questions about JSON Formatter
Why is my JSON invalid?
The usual causes are trailing commas, keys or strings in single quotes, missing quotes around keys, mismatched brackets or braces, and comments. The tool reports the parser's error message, which names the problem and its position — fix that, and validation passes.
What is the difference between formatting and validation?
Validation checks whether the text is valid JSON at all. Formatting re-indents valid JSON for readability. This tool does both: it has to validate before it can safely format, because only valid JSON can be re-serialized.
Why does JSON require double quotes?
It's part of the JSON specification. The format was deliberately kept strict — a single canonical way to write strings and keys — so any parser in any language can agree on what is valid. Single quotes are a JavaScript convenience, not valid JSON.
Can I use comments in JSON?
No. JSON does not support comments. If you need comments, consider a format like YAML, or keep notes outside the file — for example in a separate README or a schema document.
Is my data stored anywhere?
No. All processing happens locally in your browser. Your data never leaves your device, and nothing is retained after you close the tab.
Can I format large JSON files?
Yes, but very large files (10 MB+) may slow down your browser. For huge documents, paste sections or use a file-based tool on your own machine.
Does it check duplicate keys?
No. JSON.parse silently keeps the last value for a duplicated key. If that matters for your data, review the source of the JSON — this tool cannot detect the duplication.
How do I minify or compact formatted JSON for production?
You can switch to the Compact / Minify view to strip all indentation, tabs, and newlines, reducing payload size for API requests and production config files.
Why does JSON syntax disallow leading zeros and trailing commas?
The official RFC 8259 JSON specification forbids leading zeros (to avoid octal confusion in older languages) and trailing commas (to ensure deterministic parser compatibility across all programming languages).
Can I validate JSON that contains BigInt integers without precision loss?
Standard JavaScript JSON.parse parses numbers into 64-bit floating point IEEE 754 floats. Integers exceeding 2^53 - 1 (9,007,199,254,740,991) should be quoted as strings in JSON payloads to preserve precision.
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