JSON: a complete guide to syntax and working with the format

What is JSON?

JSON (JavaScript Object Notation) is a text-based data exchange format. People read it and machines parse it. Used in REST API, config files, databases and everywhere.

JSON syntax

{ 
"name": "Ivan", 
"age": 30, 
"active": true, 
"score": 9.5, 
"tags": ["dev", "js", "api"], 
"address": { 
"city": "Moscow", 
"zip": "101000" 
}, 
"phone": null 
} 

Data types

5 common mistakes

// ❌ Comma at the end (trailing comma) 
{"name": "Ivan",} 

// ❌ Single quotes 
{'name': 'Ivan'} 

// ❌ Comments (not supported!) 
{"name": "Ivan" /* author */} 

// ❌ Keys without quotes 
{name: "Ivan"} 

// ❌ undefined (not a JSON type) 
{"value": undefined} 

Working with JSON in different languages

// JavaScript 
const obj = JSON.parse('{"name":"Ivan"}'); 
const str = JSON.stringify({ name: 'Ivan' }, null, 2); 

//Python 
import json 
obj = json.loads('{"name": "Ivan"}') 
str = json.dumps({"name": "Ivan"}, indent=2, ensure_ascii=False) 

//PHP 
$obj = json_decode('{"name":"Ivan"}', true); 
$str = json_encode(["name" => "Ivan"], JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE); 

Format and validate your JSON - syntax highlighting, minification and error detection.