my_rules.json

{
  "title": "my_rules",
  "rules": [
    {
      "description": "Change caps_lock to control if pressed with other keys.",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "key_code": "caps_lock",
            "modifiers": {
              "optional": [
                "any"
              ]
            }
          },
          "to": [
            {
              "key_code": "left_control"
            }
          ],
          "to_if_alone": [
            {
              "key_code": "caps_lock",
              "hold_down_milliseconds": 500
            }
          ]
        }
      ]
    },
    {
      "description": "Post caps_lock if left_control is pressed alone.",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "key_code": "left_control",
            "modifiers": {
              "optional": [
                "any"
              ]
            }
          },
          "to": [
            {
              "key_code": "left_control"
            }
          ],
          "to_if_alone": [
            {
              "key_code": "caps_lock"
            }
          ]
        }
      ]
    }
  ]
}