{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "description": "WebHook#url_variables",
  "type": "object",
  "additionalProperties": false,
  "maxProperties": 20,
  "patternProperties": {
    "^[A-Za-z_][A-Za-z0-9_]*$": {
      "type": "string",
      "minLength": 1,
      "maxLength": 100
    }
  }
}