$ flask spec --help

Usage: flask spec [OPTIONS]

  The command (`flask spec`) to output the OpenAPI spec to stdout or a file.

  Execute `flask spec --help` to see the usage.

Options:
  -f, --format [json|yaml|yml]  The format of the spec, defaults to
                                SPEC_FORMAT config.
  -o, --output PATH             The file path to the spec file, defauts to
                                LOCAL_SPEC_PATH config.
  -i, --indent INTEGER          The indent for JSON spec, defauts to
                                LOCAL_SPEC_JSON_INDENT config.
  --help                        Show this message and exit.