diff --git a/cara/apps/calculator/__init__.py b/cara/apps/calculator/__init__.py
index c31ca372..9690fed7 100644
--- a/cara/apps/calculator/__init__.py
+++ b/cara/apps/calculator/__init__.py
@@ -88,8 +88,6 @@ class ConcentrationModel(BaseRequestHandler):
 
         try:
             form = model_generator.FormData.from_dict(requested_model_config)
-        except (KeyboardInterrupt, SystemExit):
-            raise
         except Exception as err:
             if self.settings.get("debug", False):
                 import traceback
@@ -137,7 +135,11 @@ class CompressedCalculatorFormInputs(BaseRequestHandler):
     def get(self, compressed_args: str):
         # Convert a base64 zlib encoded shortened URL into a non compressed
         # URL, and redirect.
-        args = zlib.decompress(base64.b64decode(compressed_args)).decode()
+        try:
+            args = zlib.decompress(base64.b64decode(compressed_args)).decode()
+        except Exception as err:  # noqa
+            self.set_status(400)
+            return self.finish("Invalid calculator data: it seems incomplete. Was there an error copying & pasting the URL?")
         self.redirect(f'/calculator?{args}')
 
 
@@ -156,7 +158,7 @@ def make_app(debug=False, prefix='/calculator'):
     calculator_static_dir = Path(__file__).absolute().parent / 'static'
     urls = [
         (r'/?', LandingPage),
-        (r'/c/(.*)', CompressedCalculatorFormInputs),
+        (r'/_c/(.*)', CompressedCalculatorFormInputs),
         (r'/static/(.*)', StaticFileHandler, {'path': static_dir}),
         (prefix + r'/?', CalculatorForm),
         (prefix + r'/report', ConcentrationModel),
diff --git a/cara/apps/calculator/report_generator.py b/cara/apps/calculator/report_generator.py
index a96571e6..8effd90c 100644
--- a/cara/apps/calculator/report_generator.py
+++ b/cara/apps/calculator/report_generator.py
@@ -77,16 +77,11 @@ def generate_qr_code(prefix, form: FormData):
     args = urllib.parse.urlencode(form_dict)
 
     # Then zlib compress + base64 encode the string. To be inverted by the
-    # /c/ endpoint.
-    qr_url = prefix + "/c/" + base64.b64encode(
+    # /_c/ endpoint.
+    qr_url = prefix + "/_c/" + base64.b64encode(
         zlib.compress(args.encode())
     ).decode()
-
-    # We show the human-friendly URL when hovering over the link, but for now
-    # let's keep it the same as the QR URL to ensure everything continues to work
-    # as expected (it takes more effort to validate QR barcodes than it does links).
-    # url = prefix + "/calculator/?" + args
-    url = qr_url
+    url = prefix + "/calculator?" + args
 
     qr = qrcode.QRCode(
         version=1,
@@ -101,6 +96,7 @@ def generate_qr_code(prefix, form: FormData):
     return {
         'image': img2base64(_img2bytes(img)),
         'link': url,
+        'qr_url': qr_url,
     }
 
 
diff --git a/cara/tests/apps/calculator/conftest.py b/cara/tests/apps/calculator/conftest.py
new file mode 100644
index 00000000..6e9c4074
--- /dev/null
+++ b/cara/tests/apps/calculator/conftest.py
@@ -0,0 +1,13 @@
+import pytest
+
+from cara.apps.calculator import model_generator
+
+
+@pytest.fixture
+def baseline_form_data():
+    return model_generator.baseline_raw_form_data()
+
+
+@pytest.fixture
+def baseline_form(baseline_form_data):
+    return model_generator.FormData.from_dict(baseline_form_data)
diff --git a/cara/tests/apps/calculator/test_model_generator.py b/cara/tests/apps/calculator/test_model_generator.py
index 64ecb0d4..89a3c6e0 100644
--- a/cara/tests/apps/calculator/test_model_generator.py
+++ b/cara/tests/apps/calculator/test_model_generator.py
@@ -6,15 +6,6 @@ from cara import models
 from cara import data
 import numpy as np
 
-@pytest.fixture
-def baseline_form_data():
-    return model_generator.baseline_raw_form_data()
-
-
-@pytest.fixture
-def baseline_form(baseline_form_data):
-    return model_generator.FormData.from_dict(baseline_form_data)
-
 
 def test_model_from_dict(baseline_form_data):
     form = model_generator.FormData.from_dict(baseline_form_data)
diff --git a/cara/tests/apps/calculator/test_report_generator.py b/cara/tests/apps/calculator/test_report_generator.py
index 14beade5..fb70d70b 100644
--- a/cara/tests/apps/calculator/test_report_generator.py
+++ b/cara/tests/apps/calculator/test_report_generator.py
@@ -1,19 +1,8 @@
 import pytest
 
-from cara.apps.calculator import model_generator
 from cara.apps.calculator import report_generator
 
 
-@pytest.fixture
-def baseline_form_data():
-    return model_generator.baseline_raw_form_data()
-
-
-@pytest.fixture
-def baseline_form(baseline_form_data):
-    return model_generator.FormData.from_dict(baseline_form_data)
-
-
 def test_generate_report(baseline_form):
     model = baseline_form.build_model()
 
@@ -32,4 +21,4 @@ def test_generate_report(baseline_form):
     ],
 )
 def test_readable_minutes(test_input, expected):
-    assert report_generator.readable_minutes(test_input) == expected
\ No newline at end of file
+    assert report_generator.readable_minutes(test_input) == expected
diff --git a/cara/tests/apps/calculator/test_webapp.py b/cara/tests/apps/calculator/test_webapp.py
new file mode 100644
index 00000000..24cb0819
--- /dev/null
+++ b/cara/tests/apps/calculator/test_webapp.py
@@ -0,0 +1,54 @@
+import pytest
+
+from cara.apps.calculator import make_app
+from cara.apps.calculator.report_generator import generate_qr_code
+
+
+@pytest.fixture
+def app():
+    return make_app()
+
+
+async def test_homepage(http_server_client):
+    response = await http_server_client.fetch('/')
+    assert response.code == 200
+
+
+async def test_calculator(http_server_client):
+    # Both with and without a trailing slash.
+    response = await http_server_client.fetch('/calculator')
+    assert response.code == 200
+
+    response = await http_server_client.fetch('/calculator/')
+    assert response.code == 200
+
+
+async def test_qrcode_urls(http_server_client, baseline_form):
+    prefix = 'proto://hostname/prefix'
+    qr_data = generate_qr_code(prefix, baseline_form)
+    expected = f'{prefix}/calculator?activity_type=office&air_changes=0.0'
+    assert qr_data['link'].startswith(expected)
+
+    # We should get a 200 for the link.
+    response = await http_server_client.fetch(qr_data['link'].replace(prefix, ''))
+    assert response.code == 200
+
+    # And a 302 for the QR url itself. The redirected URL should be the same as
+    # in the link.
+    assert qr_data['qr_url'].startswith(prefix)
+    response = await http_server_client.fetch(
+        qr_data['qr_url'].replace(prefix, ''),
+        max_redirects=0,
+        raise_error=False,
+    )
+    assert response.code == 302
+    assert response.headers['Location'] == qr_data['link'].replace(prefix, '')
+
+
+async def test_invalid_compressed_url(http_server_client, baseline_form):
+    response = await http_server_client.fetch(
+        '/_c/invalid-data',
+        max_redirects=0,
+        raise_error=False,
+    )
+    assert response.code == 400
diff --git a/setup.py b/setup.py
index 08afec18..0487cf14 100644
--- a/setup.py
+++ b/setup.py
@@ -71,6 +71,8 @@ setup(
         'all': [req for reqs in REQUIREMENTS.values() for req in reqs],
     },
     package_data={'cara': [
+        'apps/templates/*.j2',
+        'apps/calculator/templates/*.j2',
         'apps/calculator/*',
         'apps/calculator/*/*',
         'apps/calculator/*/*/*'