Free Free JSON Formatter - Validate & Beautify JSON Online Online

Data Types in JSON

• String: Text enclosed in double quotes: `"hello world"`
• Number: Integer or floating-point: `42`, `3.14159`, `-10`, `2.5e3`
• Boolean: True/false values: `true`, `false` (lowercase only)
• Null: Represents absence of value: `null`
• Object: Key-value pairs in curly braces: `{"name": "John", "age": 30}`
• Array: Ordered lists in square brackets: `[1, 2, 3, 4, 5]` or `["apple", "banana"]`

Syntax Rules (Critical for Valid JSON)

• Keys must be strings in double quotes: `{"name": "value"}` vs. `{name: "value"}`
• Strings must use double quotes: `"text"` vs. `'text'`
• No trailing commas: `[1, 2, 3]` vs. `[1, 2, 3,]`
• No comments allowed: JSON is pure data, no `//` or `/* */` comments
• No undefined or functions: Only the 6 data types listed above
• Boolean/null lowercase: `true`, `false`, `null`, never `True`, `FALSE`, `NULL`

1. REST API Responses

99% of modern web APIs return JSON. When you call API endpoints, responses arrive as JSON:

{
  "user": {
    "id": 12345,
    "username": "developer_pro",
    "email": "dev@example.com",
    "active": true,
    "roles": ["admin", "editor"]
  },
  "success": true
}

2. Configuration Files

Modern frameworks use JSON for configs: package.json (Node.js), tsconfig.json (TypeScript), .eslintrc.json (ESLint):

{
  "name": "my-project",
  "version": "1.0.0",
  "dependencies": {
    "react": "^18.2.0",
    "axios": "^1.4.0"
  }
}

3. Data Storage & NoSQL Databases

MongoDB stores documents as JSON-like BSON. LocalStorage/SessionStorage in browsers store data as JSON strings. Configuration management systems use JSON extensively.

Most Frequent JSON Errors

• Trailing Commas: `{"a": 1, "b": 2,}` → Remove final comma
• Single Quotes on Strings: `{'name': 'John'}` → Use double quotes: `{"name": "John"}`
• Unquoted Keys: `{name: "value"}` → Quote keys: `{"name": "value"}`
• Missing Commas: `{"a": 1 "b": 2}` → Add comma: `{"a": 1, "b": 2}`
• Unclosed Brackets: `[1, 2, 3` → Close bracket: `[1, 2, 3]`
• Comments: `{"name": "John", // comment}` → Remove comments entirely

Pro Tip: Use our JSON Formatter to automatically catch and highlight syntax errors!

JavaScript

// Parse JSON string to object
const jsonString = '{"name":"John","age":30}';
const obj = JSON.parse(jsonString);
console.log(obj.name); // "John"

// Convert object to JSON string
const data = {name: "Jane", age: 25};
const json = JSON.stringify(data);
console.log(json); // '{"name":"Jane","age":25}'

// Pretty print (formatted with indentation)
const prettyJson = JSON.stringify(data, null, 2);

Python

import json

# Parse JSON string to dictionary
json_string = '{"name": "John", "age": 30}'
data = json.loads(json_string)
print(data['name'])  # "John"

# Convert dictionary to JSON string
data = {"name": "Jane", "age": 25}
json_string = json.dumps(data)

# Pretty print
pretty_json = json.dumps(data, indent=2)

1. Consistent Key Naming: Use camelCase (`firstName`) or snake_case (`first_name`) consistently across your API/project.
2. Validate Before Parsing: Always wrap `JSON.parse()` in try-catch blocks to handle malformed JSON gracefully.
3. Minify for Production: Remove whitespace and formatting in production to reduce bandwidth (our formatter can minify).
4. Pretty Print for Development: Use formatted JSON (2-4 space indentation) for readability during development and debugging.
5. Avoid Deep Nesting: Limit nesting to 3-4 levels max for maintainability. Deeply nested JSON is hard to understand and process.
6. Include Error Handling: API responses should include status codes and error messages: `{"success": false, "error": "Invalid credentials"}`
7. Document Your Schema: Maintain documentation describing expected JSON structure, data types, and required/optional fields.
8. Use Schemas for Validation: JSON Schema provides formal validation rules ensuring data structure correctness.

• Format Messy JSON: Paste minified/unformatted JSON to automatically indent and beautify for readability.
• Validate Syntax: Catch syntax errors before deploying code. Our tool highlights exactly where JSON is invalid.
• Debug API Responses: Copy API responses directly into the formatter to understand structure and find issues.
• Minify for Production: Use minification to reduce file sizes for API responses and configuration files.
• Learn JSON Structure: Study formatted examples to understand proper syntax, nesting, and data organization.
• Compare Versions: Format two JSON files side-by-side to spot differences in data structures.