diff --git a/README.rst b/README.rst
index 6cea178..acce3b0 100644
--- a/README.rst
+++ b/README.rst
@@ -145,8 +145,8 @@ To declare a HTTP headers parameters, you must declare your argument as a `keywo
 .. _pydantic Model: https://pydantic-docs.helpmanual.io/usage/models/
 .. _keyword-only argument: https://www.python.org/dev/peps/pep-3102/
 
-Add route to generate Open Api Specification
---------------------------------------------
+Add route to generate Open Api Specification (OAS)
+--------------------------------------------------
 
 aiohttp_pydantic provides a sub-application to serve a route to generate Open Api Specification
 reading annotation in your PydanticView. Use *aiohttp_pydantic.oas.setup()* to add the sub-application
@@ -168,8 +168,8 @@ By default, the route to display the Open Api Specification is /oas but you can
 
     oas.setup(app, url_prefix='/spec-api')
 
-If you want generate the Open Api Specification from several aiohttp sub-application.
-on the same route, you must use *apps_to_expose* parameters
+If you want generate the Open Api Specification from specific aiohttp sub-applications.
+on the same route, you must use *apps_to_expose* parameter.
 
 
 .. code-block:: python3
@@ -179,9 +179,9 @@ on the same route, you must use *apps_to_expose* parameters
 
     app = web.Application()
     sub_app_1 = web.Application()
+    sub_app_2 = web.Application()
 
-    oas.setup(app, apps_to_expose=[app, sub_app_1])
-
+    oas.setup(app, apps_to_expose=[sub_app_1, sub_app_2])
 
 Add annotation to define response content
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -232,7 +232,6 @@ defined using a pydantic.BaseModel
             self.request.app["model"].remove_pet(id)
             return web.Response(status=204)
 
-
 Demo
 ----
 
@@ -247,5 +246,11 @@ Have a look at `demo`_ for a complete example
 
 Go to http://127.0.0.1:8080/oas
 
+You can generate the OAS in a json file using the command:
+
+.. code-block:: bash
+
+    python -m aiohttp_pydantic.oas demo.main
+
 
 .. _demo: https://github.com/Maillol/aiohttp-pydantic/tree/main/demo
diff --git a/aiohttp_pydantic/oas/__main__.py b/aiohttp_pydantic/oas/__main__.py
new file mode 100644
index 0000000..410cf7d
--- /dev/null
+++ b/aiohttp_pydantic/oas/__main__.py
@@ -0,0 +1,8 @@
+import argparse
+
+from .cmd import setup
+
+parser = argparse.ArgumentParser(description="Generate Open API Specification")
+setup(parser)
+args = parser.parse_args()
+args.func(args)
diff --git a/aiohttp_pydantic/oas/cmd.py b/aiohttp_pydantic/oas/cmd.py
new file mode 100644
index 0000000..b0ee01b
--- /dev/null
+++ b/aiohttp_pydantic/oas/cmd.py
@@ -0,0 +1,45 @@
+import argparse
+import importlib
+import json
+
+from .view import generate_oas
+
+
+def application_type(value):
+    """
+    Return aiohttp application defined in the value.
+    """
+    try:
+        module_name, app_name = value.split(":")
+    except ValueError:
+        module_name, app_name = value, "app"
+
+    module = importlib.import_module(module_name)
+    try:
+        if app_name.endswith("()"):
+            app_name = app_name.strip("()")
+            factory_app = getattr(module, app_name)
+            return factory_app()
+        return getattr(module, app_name)
+
+    except AttributeError as error:
+        raise argparse.ArgumentTypeError(error) from error
+
+
+def setup(parser: argparse.ArgumentParser):
+    parser.add_argument(
+        "apps",
+        metavar="APP",
+        type=application_type,
+        nargs="*",
+        help="The name of the module containing the asyncio.web.Application."
+        " By default the variable named 'app' is loaded but you can define"
+        " an other variable name ending the name of module with : characters"
+        " and the name of variable. Example: my_package.my_module:my_app",
+    )
+
+    parser.set_defaults(func=show_oas)
+
+
+def show_oas(args: argparse.Namespace):
+    print(json.dumps(generate_oas(args.apps), sort_keys=True, indent=4))
diff --git a/aiohttp_pydantic/oas/view.py b/aiohttp_pydantic/oas/view.py
index 7daa830..56d2467 100644
--- a/aiohttp_pydantic/oas/view.py
+++ b/aiohttp_pydantic/oas/view.py
@@ -1,7 +1,8 @@
 import typing
-from typing import Type
+from typing import List, Type
 
 from aiohttp.web import Response, json_response
+from aiohttp.web_app import Application
 from pydantic import BaseModel
 
 from aiohttp_pydantic.oas.struct import OpenApiSpec3, OperationObject, PathItem
@@ -106,11 +107,10 @@ def _add_http_method_to_oas(
         _OASResponseBuilder(oas_operation).build(return_type)
 
 
-async def get_oas(request):
+def generate_oas(apps: List[Application]) -> dict:
     """
-    Generate Open Api Specification from PydanticView in application.
+    Generate and return Open Api Specification from PydanticView in application.
     """
-    apps = request.app["apps to expose"]
     oas = OpenApiSpec3()
     for app in apps:
         for resources in app.router.resources():
@@ -125,7 +125,15 @@ async def get_oas(request):
                     else:
                         _add_http_method_to_oas(path, resource_route.method, view)
 
-    return json_response(oas.spec)
+    return oas.spec
+
+
+async def get_oas(request):
+    """
+    View to generate the Open Api Specification from PydanticView in application.
+    """
+    apps = request.app["apps to expose"]
+    return json_response(generate_oas(apps))
 
 
 async def oas_ui(request):
diff --git a/aiohttp_pydantic/view.py b/aiohttp_pydantic/view.py
index a899542..e04f71e 100644
--- a/aiohttp_pydantic/view.py
+++ b/aiohttp_pydantic/view.py
@@ -9,8 +9,14 @@ from aiohttp.web_exceptions import HTTPMethodNotAllowed
 from aiohttp.web_response import StreamResponse
 from pydantic import ValidationError
 
-from .injectors import (AbstractInjector, BodyGetter, HeadersGetter,
-                        MatchInfoGetter, QueryGetter, _parse_func_signature)
+from .injectors import (
+    AbstractInjector,
+    BodyGetter,
+    HeadersGetter,
+    MatchInfoGetter,
+    QueryGetter,
+    _parse_func_signature,
+)
 
 
 class PydanticView(AbstractView):
diff --git a/demo/__main__.py b/demo/__main__.py
index 5ca79a0..aea4cda 100644
--- a/demo/__main__.py
+++ b/demo/__main__.py
@@ -1,25 +1,5 @@
 from aiohttp import web
-from aiohttp.web import middleware
 
-from aiohttp_pydantic import oas
-
-from .model import Model
-from .view import PetCollectionView, PetItemView
-
-
-@middleware
-async def pet_not_found_to_404(request, handler):
-    try:
-        return await handler(request)
-    except Model.NotFound as key:
-        return web.json_response({"error": f"Pet {key} does not exist"}, status=404)
-
-
-app = web.Application(middlewares=[pet_not_found_to_404])
-oas.setup(app)
-
-app["model"] = Model()
-app.router.add_view("/pets", PetCollectionView)
-app.router.add_view("/pets/{id}", PetItemView)
+from .main import app
 
 web.run_app(app)
diff --git a/demo/main.py b/demo/main.py
new file mode 100644
index 0000000..ee4902a
--- /dev/null
+++ b/demo/main.py
@@ -0,0 +1,22 @@
+from aiohttp.web import Application, json_response, middleware
+
+from aiohttp_pydantic import oas
+
+from .model import Model
+from .view import PetCollectionView, PetItemView
+
+
+@middleware
+async def pet_not_found_to_404(request, handler):
+    try:
+        return await handler(request)
+    except Model.NotFound as key:
+        return json_response({"error": f"Pet {key} does not exist"}, status=404)
+
+
+app = Application(middlewares=[pet_not_found_to_404])
+oas.setup(app)
+
+app["model"] = Model()
+app.router.add_view("/pets", PetCollectionView)
+app.router.add_view("/pets/{id}", PetItemView)
diff --git a/tests/test_oas/test_cmd/__init__.py b/tests/test_oas/test_cmd/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_oas/test_cmd/sample.py b/tests/test_oas/test_cmd/sample.py
new file mode 100644
index 0000000..2c24c7e
--- /dev/null
+++ b/tests/test_oas/test_cmd/sample.py
@@ -0,0 +1,27 @@
+from aiohttp import web
+
+from aiohttp_pydantic import PydanticView
+
+
+class View1(PydanticView):
+    async def get(self, a: int, /):
+        return web.json_response()
+
+
+class View2(PydanticView):
+    async def post(self, b: int, /):
+        return web.json_response()
+
+
+sub_app = web.Application()
+sub_app.router.add_view("/route-2/{b}", View2)
+
+app = web.Application()
+app.router.add_view("/route-1/{a}", View1)
+app.add_subapp("/sub-app", sub_app)
+
+
+def make_app():
+    app = web.Application()
+    app.router.add_view("/route-3/{a}", View1)
+    return app
diff --git a/tests/test_oas/test_cmd/test_cmd.py b/tests/test_oas/test_cmd/test_cmd.py
new file mode 100644
index 0000000..754413a
--- /dev/null
+++ b/tests/test_oas/test_cmd/test_cmd.py
@@ -0,0 +1,120 @@
+import argparse
+from textwrap import dedent
+
+import pytest
+
+from aiohttp_pydantic.oas import cmd
+
+
+@pytest.fixture
+def cmd_line():
+    parser = argparse.ArgumentParser()
+    cmd.setup(parser)
+    return parser
+
+
+def test_show_oad_of_app(cmd_line, capfd):
+    args = cmd_line.parse_args(["tests.test_oas.test_cmd.sample"])
+    args.func(args)
+    captured = capfd.readouterr()
+    expected = dedent(
+        """
+        {
+        "openapi": "3.0.0",
+        "paths": {
+            "/route-1/{a}": {
+                "get": {
+                    "parameters": [
+                        {
+                            "in": "path",
+                            "name": "a",
+                            "required": true,
+                            "schema": {
+                                "type": "integer"
+                            }
+                        }
+                    ]
+                }
+            },
+            "/sub-app/route-2/{b}": {
+                "post": {
+                    "parameters": [
+                        {
+                            "in": "path",
+                            "name": "b",
+                            "required": true,
+                            "schema": {
+                                "type": "integer"
+                            }
+                        }
+                    ]
+                }
+            }
+        }
+    }
+    """
+    )
+
+    assert captured.out.strip() == expected.strip()
+
+
+def test_show_oad_of_sub_app(cmd_line, capfd):
+    args = cmd_line.parse_args(["tests.test_oas.test_cmd.sample:sub_app"])
+    args.func(args)
+    captured = capfd.readouterr()
+    expected = dedent(
+        """
+        {
+        "openapi": "3.0.0",
+        "paths": {
+            "/sub-app/route-2/{b}": {
+                "post": {
+                    "parameters": [
+                        {
+                            "in": "path",
+                            "name": "b",
+                            "required": true,
+                            "schema": {
+                                "type": "integer"
+                            }
+                        }
+                    ]
+                }
+            }
+        }
+    }
+    """
+    )
+
+    assert captured.out.strip() == expected.strip()
+
+
+def test_show_oad_of_a_callable(cmd_line, capfd):
+    args = cmd_line.parse_args(["tests.test_oas.test_cmd.sample:make_app()"])
+    args.func(args)
+    captured = capfd.readouterr()
+    expected = dedent(
+        """
+        {
+        "openapi": "3.0.0",
+        "paths": {
+            "/route-3/{a}": {
+                "get": {
+                    "parameters": [
+                        {
+                            "in": "path",
+                            "name": "a",
+                            "required": true,
+                            "schema": {
+                                "type": "integer"
+                            }
+                        }
+                    ]
+                }
+            }
+        }
+    }
+    """
+    )
+
+    assert captured.out.strip() == expected.strip()