What does a JSON formatter do?

It takes unformatted JSON (one-line or inconsistently indented) and rewrites it with uniform spacing and line breaks for readability. It also flags syntax errors.

Does my JSON get uploaded?

No. Formatting runs 100% in your browser via JSON.parse and JSON.stringify. The content never leaves your device — perfect for sensitive data.

Why do some valid-looking JSONs fail?

Strict JSON forbids comments, trailing commas, single quotes and unquoted keys. These are common in JavaScript but break the JSON parser.

Free JSON Formatter

Why formatting JSON matters

In production, JSON usually travels minified: one line, no spaces, no breaks. That saves bytes but makes it unreadable. When you're debugging an API response, scanning a long config, or auditing a database export, the first move is to format. A good formatter turns a soup of characters into a clear hierarchical structure in under a second.

Strict JSON rules

Double quotes only. JSON doesn't accept single quotes. 'name' breaks the parser; "name" works.
No trailing commas. {"a":1,} is valid JavaScript but invalid JSON.
No comments. No // and no /* */. If you need comments, use JSON5 or JSONC (VS Code's variant).
Keys always quoted. {name: "Genfy"} breaks; {"name": "Genfy"} works.
Booleans lowercase. true and false, not True.

Valid data types

JSON supports six types: string, number, boolean, null, object and array. No dates (represented as ISO strings), no undefined (the key gets dropped), no functions, no symbols. When a library serializes a JavaScript object to JSON, anything outside those six types disappears silently.

Indentation: 2 spaces, 4 spaces or tab

No universal standard. The most common convention in JavaScript projects is 2 spaces (npm package.json, Prettier default). Python leans toward 4. Some teams use tabs for accessibility reasons. What matters is consistency inside a project: if your repo uses 2 spaces, don't introduce files with 4.

Common syntax errors

Trailing comma at the end of an array or object. Often comes from deleting the last line without updating the previous comma.
Smart quotes. When you copy from Word or Google Docs, regular quotes get auto-replaced with curly quotes (" ") that JSON doesn't understand.
Control characters in strings. Literal tabs and newlines inside strings break the parser; they must be escaped as \t and \n.
Mismatched braces or brackets.

Tips for working with large JSON

If your file is over 10 MB, avoid web editors — they may freeze the browser. Use a CLI tool like jq to filter and reformat. To inspect part of the structure, try jq 'keys' to list top-level keys before going deeper.

JSON vs modern alternatives

JSON5: allows comments, trailing commas, unquoted keys. Useful for configs.
YAML: more readable but ambiguous (an unquoted value can be parsed as string or number).
TOML: popular in Rust and some config files (Cargo, pyproject.toml).
Protocol Buffers: binary, much more efficient than JSON for internal service-to-service traffic.

JSON Formatter