diff --git a/functions/firebase/main.py b/functions/firebase/main.py
index 0e24d93d748f..8febbfc366c6 100644
--- a/functions/firebase/main.py
+++ b/functions/firebase/main.py
@@ -24,6 +24,10 @@
 # [END functions_firebase_firestore]
 # [END functions_firebase_auth]
 
+# [START functions_firebase_reactive]
+from google.cloud import firestore
+# [END functions_firebase_reactive]
+
 
 # [START functions_firebase_rtdb]
 def hello_rtdb(data, context):
@@ -75,6 +79,28 @@ def hello_auth(data, context):
 # [END functions_firebase_auth]
 
 
+# [START functions_firebase_reactive]
+client = firestore.Client()
+
+
+# Converts strings added to /messages/{pushId}/original to uppercase
+def make_upper_case(data, context):
+    path_parts = context.resource.split('/documents/')[1].split('/')
+    collection_path = path_parts[0]
+    document_path = '/'.join(path_parts[1:])
+
+    affected_doc = client.collection(collection_path).document(document_path)
+
+    cur_value = data["value"]["fields"]["original"]["stringValue"]
+    new_value = cur_value.upper()
+    print(f'Replacing value: {cur_value} --> {new_value}')
+
+    affected_doc.set({
+        u'original': new_value
+    })
+# [END functions_firebase_reactive]
+
+
 # [START functions_firebase_analytics]
 def hello_analytics(data, context):
     print(data)
diff --git a/functions/firebase/main_test.py b/functions/firebase/main_test.py
index ff10bf672e60..d4404834a1e9 100644
--- a/functions/firebase/main_test.py
+++ b/functions/firebase/main_test.py
@@ -12,8 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from collections import UserDict
 from datetime import datetime
 import json
+import uuid
+
+from mock import MagicMock, patch
 
 import main
 
@@ -76,6 +80,43 @@ def test_auth(capsys):
     assert 'Email: me@example.com' in out
 
 
+@patch('main.client')
+def test_make_upper_case(firestore_mock, capsys):
+
+    firestore_mock.collection = MagicMock(return_value=firestore_mock)
+    firestore_mock.document = MagicMock(return_value=firestore_mock)
+    firestore_mock.set = MagicMock(return_value=firestore_mock)
+
+    user_id = str(uuid.uuid4())
+    date_string = datetime.now().isoformat()
+    email_string = '%s@%s.com' % (uuid.uuid4(), uuid.uuid4())
+
+    data = {
+        'uid': user_id,
+        'metadata': {'createdAt': date_string},
+        'email': email_string,
+        'value': {
+            'fields': {
+                'original': {
+                    'stringValue': 'foobar'
+                }
+            }
+        }
+    }
+
+    context = UserDict()
+    context.resource = '/documents/some_collection/path/some/path'
+
+    main.make_upper_case(data, context)
+
+    out, _ = capsys.readouterr()
+
+    assert 'Replacing value: foobar --> FOOBAR' in out
+    firestore_mock.collection.assert_called_with('some_collection')
+    firestore_mock.document.assert_called_with('path/some/path')
+    firestore_mock.set.assert_called_with({'original': 'FOOBAR'})
+
+
 def test_analytics(capsys):
     timestamp = int(datetime.utcnow().timestamp())
 
diff --git a/functions/firebase/requirements.txt b/functions/firebase/requirements.txt
new file mode 100644
index 000000000000..dac97c81fed7
--- /dev/null
+++ b/functions/firebase/requirements.txt
@@ -0,0 +1 @@
+google-cloud-firestore==0.29.0