diff --git a/smoke_test.py b/smoke_test.py
new file mode 100644
index 00000000..981d4bac
--- /dev/null
+++ b/smoke_test.py
@@ -0,0 +1,87 @@
+"""
+Smoke test for a running stack: opens every site and the admin login.
+
+    docker compose exec web python smoke_test.py [base_url]
+
+Needs no extra packages, so it runs the same on every Python/Django version.
+Exits non-zero if anything fails. Expects the sample data (SEED_DUMMY_DATA).
+"""
+import json
+import os
+import re
+import sys
+import urllib.error
+import urllib.parse
+import urllib.request
+from http.cookiejar import CookieJar
+
+from utils.sample_sites import SITE_TEXTS
+
+BASE = sys.argv[1] if len(sys.argv) > 1 else 'http://127.0.0.1:8000'
+ADMIN = ('dummy-admin@example.com',
+         os.environ.get('DUMMY_ADMIN_PASSWORD') or 'dummy-admin')
+SUB_PAGES = ['about', 'services', 'pricing', 'contact']
+failures = []
+
+
+def fetch(opener, path, host, data=None):
+    request = urllib.request.Request(BASE + path, data=data)
+    request.add_header('Host', host)
+    try:
+        response = opener.open(request, timeout=60)
+    except urllib.error.HTTPError as error:
+        return error.code, error.read().decode('utf-8', 'replace'), path
+    return (response.status if hasattr(response, 'status')
+            else response.getcode(),
+            response.read().decode('utf-8', 'replace'), response.geturl())
+
+
+def check(name, ok, detail=''):
+    print('{} {}{}'.format('ok  ' if ok else 'FAIL', name,
+                           '' if ok else '  -> ' + detail))
+    if not ok:
+        failures.append(name)
+
+
+def sites():
+    configs = json.loads(os.environ.get('UNGLEICH_SITE_CONFIGS') or '{}')
+    return sorted(d for d in configs if ':' not in d)
+
+
+def main():
+    for domain in sites():
+        opener = urllib.request.build_opener(
+            urllib.request.HTTPCookieProcessor(CookieJar()))
+        name, tagline = SITE_TEXTS.get(domain, (domain, ''))
+        status, body, _ = fetch(opener, '/', domain)
+        check('{} /'.format(domain), status == 200, 'status %s' % status)
+        status, body, _ = fetch(opener, '/en-us/cms/', domain)
+        check('{} home'.format(domain),
+              status == 200 and name in body and tagline in body,
+              'status %s, content missing' % status)
+        for slug in SUB_PAGES:
+            status, _, _ = fetch(opener, '/en-us/cms/%s/' % slug, domain)
+            check('{} {}'.format(domain, slug), status == 200,
+                  'status %s' % status)
+
+    # admin login on the first site
+    domain = sites()[0]
+    opener = urllib.request.build_opener(
+        urllib.request.HTTPCookieProcessor(CookieJar()))
+    status, body, _ = fetch(opener, '/en-us/admin/login/', domain)
+    token = re.search(r"name=.csrfmiddlewaretoken. value=.([^'\"]+)", body)
+    check('admin login page', status == 200 and token, 'status %s' % status)
+    if token:
+        form = urllib.parse.urlencode({
+            'csrfmiddlewaretoken': token.group(1), 'username': ADMIN[0],
+            'password': ADMIN[1], 'next': '/en-us/admin/'}).encode()
+        status, body, url = fetch(
+            opener, '/en-us/admin/login/', domain, data=form)
+        check('admin login works',
+              status == 200 and 'login' not in url, 'status %s, ended on %s' % (status, url))
+
+    print('\n{} failure(s)'.format(len(failures)))
+    sys.exit(1 if failures else 0)
+
+
+main()
diff --git a/utils/management/commands/seed_dummy_data.py b/utils/management/commands/seed_dummy_data.py
index d50fbca6..8a8c562c 100644
--- a/utils/management/commands/seed_dummy_data.py
+++ b/utils/management/commands/seed_dummy_data.py
@@ -24,25 +24,13 @@ from django.contrib.sites.models import Site
 from django.core.management.base import BaseCommand
 
 from membership.models import CustomUser
+from utils.sample_sites import SITE_TEXTS
 
 REVERSE_ID = 'dummy-home'
 ADMIN_EMAIL = 'dummy-admin@example.com'
 CUSTOMER_EMAIL_FORMAT = 'dummy-customer-{}@example.com'
 CUSTOMER_COUNT = 12
 DEFAULT_ADMIN_PASSWORD = 'dummy-admin'
-# domain -> (name, tagline); other domains are named after their domain
-SITE_TEXTS = {
-    'ungleich.ch': ('ungleich', 'Swiss IT infrastructure, hosting and open source.'),
-    'blog.ungleich.ch': ('ungleich blog', 'Notes from running data centers, networks and free software.'),
-    'comic.ungleich.ch': ('ungleich comic', 'Life in the data center, one panel at a time.'),
-    'digitalglarus.ch': ('Digital Glarus', 'The Swiss IT valley in Schwanden, Glarus.'),
-    'datacenterlight.ch': ('Data Center Light', 'Virtual machines from a Swiss, ecological data center.'),
-    'rails-hosting.ch': ('Rails Hosting', 'Managed hosting for Ruby on Rails applications.'),
-    'django-hosting.ch': ('Django Hosting', 'Managed hosting for Django applications.'),
-    'node-hosting.ch': ('Node.js Hosting', 'Managed hosting for Node.js applications.'),
-    'devuanhosting.ch': ('Devuan Hosting', 'Hosting on Devuan, the systemd-free Linux.'),
-    'devuanhosting.com': ('Devuan Hosting', 'Hosting on Devuan, the systemd-free Linux.'),
-}
 # (slug, title, text) for the pages below each site's home page
 SUB_PAGES = [
     ('about', 'About', '{name} is operated by ungleich GmbH in Switzerland. '
diff --git a/utils/sample_sites.py b/utils/sample_sites.py
new file mode 100644
index 00000000..09fd3b74
--- /dev/null
+++ b/utils/sample_sites.py
@@ -0,0 +1,15 @@
+"""Sample site names and taglines, shared by the seeder and smoke_test.py.
+No Django imports, so it works anywhere."""
+# domain -> (name, tagline); other domains are named after their domain
+SITE_TEXTS = {
+    'ungleich.ch': ('ungleich', 'Swiss IT infrastructure, hosting and open source.'),
+    'blog.ungleich.ch': ('ungleich blog', 'Notes from running data centers, networks and free software.'),
+    'comic.ungleich.ch': ('ungleich comic', 'Life in the data center, one panel at a time.'),
+    'digitalglarus.ch': ('Digital Glarus', 'The Swiss IT valley in Schwanden, Glarus.'),
+    'datacenterlight.ch': ('Data Center Light', 'Virtual machines from a Swiss, ecological data center.'),
+    'rails-hosting.ch': ('Rails Hosting', 'Managed hosting for Ruby on Rails applications.'),
+    'django-hosting.ch': ('Django Hosting', 'Managed hosting for Django applications.'),
+    'node-hosting.ch': ('Node.js Hosting', 'Managed hosting for Node.js applications.'),
+    'devuanhosting.ch': ('Devuan Hosting', 'Hosting on Devuan, the systemd-free Linux.'),
+    'devuanhosting.com': ('Devuan Hosting', 'Hosting on Devuan, the systemd-free Linux.'),
+}