Could you please let us know why you need to know how the documentation is generated? There may be no immediate need for this information, as the documentation aims to follow OpenAPI rules. If you have an SDK and have built new endpoints for the router, this knowledge would not be helpful, as the SDK does not include API documentation files.
we would like to visualize our OpenAPI specification also so beautiful.
Sorry for being not precise. I mean what software / library was used to visualize the REST API documentation