Build OpenAPI spec for a sanic app without starting the server

build_spec.py

import json

from sanic import Sanic
from sanic_ext.extensions.openapi.builders import SpecificationBuilder


app = Sanic(__name__)


def get_spec(a: Sanic):
    return SpecificationBuilder().build(a).serialize()


@app.command
def openapi():
    with open("./openapi.json", "w") as f:
        f.write(json.dumps(get_spec(app)))


if __name__ == "__main__":
    app.run()