What is JSON?
JSON (JavaScript Object Notation) is one of the most widely used formats for storing and exchanging data on the internet. You’ll encounter it whenever an app communicates with a server, reads a configuration file, or saves structured information. It’s a plain-text format that organizes data into key-value pairs and lists, making it both human-readable and easy for computers to process.
When JSON is transmitted over networks or generated by programs, it’s often compressed into a single line — all whitespace removed — to save bandwidth. While that’s efficient for machines, it’s nearly impossible for humans to read or debug.
What Does This Tool Do?
This tool takes raw or minified JSON and transforms it into a clean, properly indented structure. It also validates the JSON, catching common mistakes like missing commas, unclosed brackets, or incorrect quoting. Color-coded syntax highlighting makes it easy to distinguish keys, values, strings, numbers, booleans, and null values at a glance.
How to Use This Tool
- Paste your JSON text into the input area on the left.
- The formatted result appears instantly on the right with syntax highlighting.
- If there’s an error in your JSON, a message will indicate where the problem is.
- Use the copy button to grab the formatted output.
No button to press — formatting happens automatically as you type or paste. To study a long result without the input taking up half the screen, switch the View control to Output — the formatted JSON expands to the full width.
Common Use Cases
- Debugging API responses: Paste a raw response from a web API to inspect its structure clearly.
- Reading config files: Make sense of minified
package.json,tsconfig.json, or other configuration files. - Preparing data: Clean up JSON before pasting it into documentation, a code review, or a ticket.
- Validating structure: Quickly check whether JSON you’ve written manually is syntactically correct.
The Errors You’ll Actually Hit
JSON’s grammar is small, so invalid JSON almost always fails for one of these reasons:
| Symptom | Cause | Fix |
|---|---|---|
Unexpected token ' | Single quotes used | JSON requires double quotes: "key", not 'key' |
Unexpected token } | Trailing comma | Remove the comma after the last item |
Unexpected token a (or similar) | Unquoted key or value | Quote all keys; strings must be quoted |
Unexpected end of input | Unclosed bracket or brace | Count your { } and [ ] pairs |
Bad escaped character | Raw backslash in a string | Escape it: "C:\\path", not "C:\path" |
| Works in JS, fails here | Comments in the JSON | JSON has no comments — remove // and /* */ |
NaN/Infinity rejected | Non-standard number values | JSON only allows finite numbers; use null or a string |
The last two surprise people most: JavaScript object literals accept comments, single quotes, and unquoted keys — JSON does not. “JSON” that came from a JavaScript file often needs those fixed first.
JSON’s Six Types
Everything in JSON is built from six types: strings ("text", double quotes only), numbers (42, 3.14, -1e9 — no leading zeros, no hex), booleans (true/false, lowercase), null, arrays ([1, 2, 3]), and objects ({"key": "value"}). Notably absent: dates (use ISO 8601 strings like "2026-07-04"), comments, and undefined. Every valid JSON document is one value of one of these types — usually an object or array at the top level.
Indentation: 2 Spaces, 4 Spaces, or Tabs?
There’s no wrong answer, but conventions exist: 2 spaces dominates the JavaScript/web ecosystem (npm’s package.json uses it), 4 spaces is common in Python-adjacent tooling and improves readability for deeply nested data, and tabs let every reader choose their own width. For minimum file size in transit, no formatting at all (minified) is correct — formatting is for humans, so pick what your team reads most comfortably.
Frequently Asked Questions
Is my data safe?
Yes. All processing happens directly in your browser — your data is never sent to any server. You can even use this tool offline once the page has loaded.
What errors does the validator catch?
The tool detects syntax errors such as trailing commas, mismatched brackets, unquoted keys, and invalid escape sequences. It shows the line and position of the error so you can fix it quickly.
Does it support large files?
Yes, it handles large JSON documents well. For very large payloads, performance depends on your device’s processing power, but most real-world use cases work instantly.
Why is my JSON valid in JavaScript but rejected here?
Because JavaScript object syntax is more permissive than JSON. Single quotes, unquoted keys, trailing commas, comments, NaN, and undefined are all legal in JavaScript but illegal in JSON. This validator follows the strict JSON standard (RFC 8259) — the same rules an API or JSON.parse will apply.
What's the difference between formatting and minifying?
Formatting adds whitespace for human readability; minifying removes it so machines transfer fewer bytes. Both produce the same data. Format when debugging or reviewing; minify when embedding JSON in a URL or shaving payload size.