diff --git a/assets/css/base.css b/assets/css/base.css
index 6916ad17..6bb4bc4f 100644
--- a/assets/css/base.css
+++ b/assets/css/base.css
@@ -99,6 +99,25 @@ h5 {
   border-bottom: 1px solid #e0e0e0;
 }
 
+.alert-warning {
+  background-color: #fff3cd;
+  border-color: #ffeeba;
+  color: #856404;
+  padding: 15px;
+  margin-bottom: 20px;
+  border-radius: 4px;
+}
+
+.alert-warning .alert-link {
+  color: #856404;
+  font-weight: bold;
+  text-decoration: underline;
+}
+
+.alert-warning .alert-link:hover {
+  color: #604c2e;
+}
+
 /* Responsive Styles */
 @media (max-width: 768px) {
   .navbar .container {
diff --git a/main.py b/main.py
index f42bc366..221227bd 100644
--- a/main.py
+++ b/main.py
@@ -3,6 +3,7 @@ from jinja2 import TemplateNotFound
 
 import json
 import pathlib
+import os
 
 from argparse import ArgumentParser
 
@@ -21,15 +22,32 @@ def catch_all(path):
         services = json.loads(
             (pathlib.Path(__file__).parent / "services.json").read_text()
         )
-        return render_template(f"{path}.html", services=services)
+
+        warning = None
+
+        if app.development_mode:
+            warning = render_template("prod-warning.html")
+
+        return render_template(
+            f"{path}.html", services=services, warning=warning
+        )
     except TemplateNotFound:
         return "404 Not Found", 404
 
 
+app.development_mode = False
+
+if os.environ.get("PRIVATECOFFEE_DEV"):
+    app.development_mode = True
+
+
 if __name__ == "__main__":
     parser = ArgumentParser(description="Run the private.coffee web server.")
     parser.add_argument("--port", type=int, default=9810)
     parser.add_argument("--debug", action="store_true")
+    parser.add_argument("--dev", action="store_true")
     args = parser.parse_args()
 
+    app.development_mode = args.dev or app.development_mode
+
     app.run(port=args.port, debug=args.debug)
diff --git a/templates/base.html b/templates/base.html
index d759727b..13593f78 100644
--- a/templates/base.html
+++ b/templates/base.html
@@ -51,6 +51,7 @@
             </ul><a class="btn btn-primary shadow navbar-btn" role="button" href="/membership.html">JOIN &amp; REBEL</a>
         </div>
     </nav>
+    {% if warning %}{{ warning|safe }}{% endif %}
     {% block content %}{% endblock %}
     <footer class="bg-primary-gradient">
       <div class="container py-4 py-lg-5">
diff --git a/templates/prod-warning.html b/templates/prod-warning.html
new file mode 100644
index 00000000..35c1bd9e
--- /dev/null
+++ b/templates/prod-warning.html
@@ -0,0 +1,6 @@
+<div class="alert alert-warning text-center" role="alert">
+  This is a development version of the Private.coffee website. For the live
+  version, please visit
+  <a href="https://private.coffee" class="alert-link">https://private.coffee</a
+  >.
+</div>