schema.json

{
  "$ref": "#/definitions/MyType",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "definitions": {
    "MyType": {
      "items": [
        {
          "additionalProperties": false,
          "properties": {
            "a": {
              "type": "string"
            }
          },
          "required": [
            "a"
          ],
          "type": "object"
        },
        {
          "additionalProperties": false,
          "properties": {
            "b": {
              "type": "number"
            }
          },
          "required": [
            "b"
          ],
          "type": "object"
        },
        {
          "additionalProperties": false,
          "properties": {
            "c": {
              "type": "boolean"
            }
          },
          "required": [
            "c"
          ],
          "type": "object"
        }
      ],
      "maxItems": 3,
      "minItems": 3,
      "type": "array"
    }
  }
}