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JSON

Full form - JavaScript Object Notation Lightweight, fast, web standard. NO comments.

Syntax​

{
  "app": "MyApp",
  "version": "1.0.0",
  "debug": true,
  "port": 8080,
  "database": {
    "host": "localhost",
    "port": 5432,
    "name": "mydb"
  },
  "features": ["auth", "logging", "cache"],
  "timeout": null
}

Data types​

{
  "string": "Hello World",
  "number": 42,
  "float": 3.14,
  "boolean": true,
  "null_value": null,
  "array": [1, 2, 3],
  "object": {"key": "value"}
}

Pros ✅​

  • Fast parsing
  • Wide language support
  • No comments (sometimes good, sometimes bad)
  • Small file size
  • Web API standard

Cons ❌​

  • NO comments allowed
  • NO multi-line strings
  • NO trailing commas (breaks)
  • Strict syntax

When to Use​

  • API configs
  • package.json, tsconfig.json
  • Simple, flat data
  • Mobile apps (size matters)
  • Web applications

Python Usage​

import json

# Read
with open('config.json') as f:
    config = json.load(f)

# Write
config = {'host': 'localhost', 'port': 8080}
with open('config.json', 'w') as f:
    json.dump(config, f, indent=2)

# Access
port = config['database']['port']

Common Mistake​

❌ Trailing commas break JSON:

{
  "key": "value",  // ← Will break parser
}

✅ Remove trailing commas:

{
  "key": "value"
}

Validation​

from pydantic import BaseModel

class Config(BaseModel):
    host: str
    port: int
    debug: bool = False

# This will validate on load
config = Config(**json.load(f))

Tools​

# Pretty print
jq '.' config.json

# Query values
jq '.database.host' config.json

# Validate
python -m json.tool config.json