JSON Basics: The Punctuation That Breaks Files

JSON is a popular format for storing data, used by websites, apps and settings files. It's plain text, so you can read and edit it in any editor, but it is picky about punctuation.

What JSON looks like

{
  "name": "Ana",
  "age": 34,
  "active": true,
  "languages": ["English", "Portuguese"],
  "address": {
    "city": "Lisbon"
  }
}

The building blocks

Piece	Written as	Example
Object	curly braces	{ ... }
Array (list)	square brackets	[ ... ]
Key	text in double quotes	"name"
String	text in double quotes	"Ana"
Number	digits, no quotes	34
Boolean	true or false, no quotes	true
Null	the word null	null

The rules

1. Keys and strings use double quotes. Single quotes are not valid.
2. Separate items with commas.
3. No comma after the last item. This is the most common mistake.
4. Every opening bracket needs a closing one.
5. Keys are followed by a colon.
6. JSON has no comments.

Common errors

Mistake	Example
Trailing comma	"age": 34, before a closing brace
Missing comma	between two items
Single quotes	'name' instead of "name"
Unquoted key	name: "Ana"
Missing bracket	an unclosed { or [
Comments	// note inside the file

Editing safely

1. Copy the file first.
2. Change values, not structure, if you can.
3. Watch the commas when you add or remove lines.
4. Keep indentation neat, since it helps you see nesting.
5. Use a validator if you're unsure, before using the file.

Special characters in strings

Some characters must be escaped with a backslash: a double quote is ", a backslash is \, and a new line is \n.

Uses

• App settings.
• Data from websites and APIs.
• Configuration for tools.

A calm approach

If a JSON file stops working after an edit, the problem is almost always a missing or extra comma or bracket. Compare with your backup and look at the line just before the error.

Reading JSON

Even without editing, learning to read JSON helps you understand the data your apps use.

Get Notepad+ Text Editor →