JSON, YAML and XML

Automation tools exchange structured data, not screen output. Three formats cover almost everything on the CCNA. They all carry the same idea - keys and values, lists, and nesting - but look different.

JSON

JSON (JavaScript Object Notation) is the most common, especially in REST. { } is an object (keys and values), [ ] is a list (array). Strings are in double quotes; values can be numbers, true/false, or null. Commas separate items; no comma after the last one.

{
  "interface": {
    "name": "GigabitEthernet0/1",
    "enabled": true,
    "speed": 1000,
    "addresses": [
      { "ip": "10.1.1.1", "mask": "255.255.255.0" }
    ],
    "vlans": [1, 10, 20]
  }
}

YAML

YAML is easier for people to write - no braces, just indentation (spaces, never tabs). A list item starts with -. Ansible playbooks are YAML.

interface:
  name: GigabitEthernet0/1
  enabled: true
  speed: 1000
  addresses:
    - ip: 10.1.1.1
      mask: 255.255.255.0
  vlans:
    - 1
    - 10
    - 20

XML

XML wraps every value in opening and closing tags. It's older and more verbose; NETCONF uses it.

<interface>
  <name>GigabitEthernet0/1</name>
  <enabled>true</enabled>
  <speed>1000</speed>
  <address>
    <ip>10.1.1.1</ip>
    <mask>255.255.255.0</mask>
  </address>
</interface>

Common mistake: The commonest JSON error is a stray comma after the last item in an object or list, or single quotes instead of double. YAML's commonest error is a tab instead of spaces, or crooked indentation.

Remember: JSON: braces and brackets, double quotes, no trailing comma. YAML: indentation and dashes. XML: open/close tags. Same data, three looks.