Is it safe to paste sensitive JSON into an online formatter?

With ilovedev, yes — formatting runs entirely in your browser via JSON.parse/stringify. Nothing is uploaded. Avoid tools that POST your data to a server.

Why does valid-looking JSON fail to parse?

The usual suspects are trailing commas, single quotes, comments, or unquoted keys. The parser error points to the exact character; formatting the input makes the problem obvious.

What is the difference between formatting and minifying?

Formatting adds indentation and newlines for readability. Minifying strips all whitespace to shrink the payload — useful for production API responses.

Can JSON have comments?

No. The spec forbids them. Some supersets (JSON5, JSONC) allow comments, but standard JSON.parse will reject them.

JSON explained: format, validate, and fix common errors

6 min readUpdated May 24, 2026

JSON (JavaScript Object Notation) is the lingua franca of web APIs and config files. It is simple — but a single trailing comma or smart quote can break a whole payload. This guide covers the rules, the tooling, and the errors you will actually hit.

What JSON is (and is not)

JSON is a text format for structured data built from two structures: objects ({ "key": value }) and arrays ([ value, value ]). Values can be a string, number, boolean, null, object, or array — nothing else.

Crucially, JSON is *not* JavaScript. It has no comments, no functions, no undefined, no trailing commas, and keys must be double-quoted strings.

{
  "name": "ada",
  "active": true,
  "roles": ["admin", "dev"],
  "meta": null
}

The 5 rules that trip people up

Double quotes only. 'single' quotes are invalid. So are unquoted keys.
No trailing commas. [1, 2, 3,] is valid JavaScript but invalid JSON.
No comments. // like this will fail. Strip them before parsing.
Numbers are plain. No leading zeros, no NaN, no Infinity.
Escape special characters in strings: \n, \t, \", and \\.

How to format and validate JSON

Formatting (or "beautifying") adds consistent indentation so nested data is readable; validating confirms the document actually parses. Both happen in one step when you paste into the JSON Formatter — it runs entirely in your browser, so even secrets stay local.

Programmatically, the browser and Node give you this for free:

const obj = JSON.parse(raw)            // validate + parse
const pretty = JSON.stringify(obj, null, 2) // format with 2-space indent
const min = JSON.stringify(obj)        // minify

Common parse errors and their fixes

"Unexpected token } in JSON"

Almost always a trailing comma before the closing brace or bracket. Remove it.

"Unexpected token ' in JSON"

You used single quotes. Replace every ' around keys and string values with ".

"Unexpected end of JSON input"

The document is truncated — a brace or bracket is unclosed. Format the JSON and the editor will show where nesting breaks.

Pasting an API response that looks fine but won’t parse? It may be double-encoded (a JSON string *inside* a JSON string). Decode once, then parse again.

Converting JSON to other formats

Once your JSON is valid, converting is trivial. Turn it into YAML for config files with the JSON ↔ YAML converter, into a spreadsheet with JSON ↔ CSV, or into XML for legacy systems.

Frequently asked questions

Is it safe to paste sensitive JSON into an online formatter?: With ilovedev, yes — formatting runs entirely in your browser via JSON.parse/stringify. Nothing is uploaded. Avoid tools that POST your data to a server.
Why does valid-looking JSON fail to parse?: The usual suspects are trailing commas, single quotes, comments, or unquoted keys. The parser error points to the exact character; formatting the input makes the problem obvious.
What is the difference between formatting and minifying?: Formatting adds indentation and newlines for readability. Minifying strips all whitespace to shrink the payload — useful for production API responses.
Can JSON have comments?: No. The spec forbids them. Some supersets (JSON5, JSONC) allow comments, but standard JSON.parse will reject them.

Try it yourself

Put this guide into practice — these tools run free in your browser.

JSON Formatter & Validator JSON ↔ YAML Converter JSON ↔ CSV Converter JSON to XML Converter