Karbiner Complex Rules

custom.json

{
  "title": "Caps and return to ctrl. Ctrl to caps.",
  "rules": [
    {
      "description": "Post left_ctrl when return_or_enter is hold.",
      "manipulators": [
        {
          "from": {
            "key_code": "return_or_enter",
            "modifiers": {
              "optional": [
                "any"
              ]
            }
          },
          "to": [
            {
              "key_code": "right_control"
            }
          ],
          "to_if_alone": [
            {
              "key_code": "return_or_enter"
            }
          ],
          "type": "basic"
        }
      ]
    },
    {
      "description": "Post escape if caps is pressed alone, left_ctrl otherwise",
      "manipulators": [
        {
          "from": {
            "key_code": "caps_lock",
            "modifiers": {
              "optional": [
                "any"
              ]
            }
          },
          "to": [
            {
              "key_code": "left_control"
            }
          ],
          "to_if_alone": [
            {
              "key_code": "escape"
            }
          ],
          "type": "basic"
        }
      ]
    },
    {
      "description": "Map left_ctrl to caps_lock.",
      "manipulators": [
        {
          "from": {
            "key_code": "left_control",
            "modifiers": {
              "optional": [
                "any"
              ]
            }
          },
          "to": [
            {
              "key_code": "caps_lock"
            }
          ],
          "type": "basic"
        }
      ]
    }
  ]
}

open "karabiner://karabiner/assets/complex_modifications/import?url=https://gist.githubusercontent.com/rahulrrixe/789413c5fb9629cbb8114d900a7602ac/raw/ef53711e5fd45b2cba11de6d0ef0d1c82470aa01/custom.json"