diff --git a/src/edge_proxy/settings.py b/src/edge_proxy/settings.py
index 96be2c7..d4e2b90 100644
--- a/src/edge_proxy/settings.py
+++ b/src/edge_proxy/settings.py
@@ -8,17 +8,15 @@
 
 import structlog
 
-from pydantic import AliasChoices, BaseModel, HttpUrl, IPvAnyAddress, Field
+from pydantic import AliasChoices, BaseModel, HttpUrl, IPvAnyAddress, Field, constr
 
 from pydantic_settings import BaseSettings, PydanticBaseSettingsSource
 
-
 CONFIG_PATH = os.environ.get(
     "CONFIG_PATH",
     default="config.json",
 )
 
-
 logger = structlog.get_logger()
 
 
@@ -65,8 +63,8 @@ def json_config_settings_source() -> dict[str, Any]:
 
 
 class EnvironmentKeyPair(BaseModel):
-    server_side_key: str
-    client_side_key: str
+    server_side_key: constr(pattern=r"ser\.*", strip_whitespace=True)
+    client_side_key: constr(min_length=1, strip_whitespace=True)
 
 
 class EndpointCacheSettings(BaseModel):
@@ -105,14 +103,7 @@ class HealthCheckSettings(BaseModel):
 
 
 class AppSettings(BaseModel):
-    environment_key_pairs: list[EnvironmentKeyPair] = Field(
-        default_factory=lambda: [
-            EnvironmentKeyPair(
-                server_side_key="ser.environment_key",
-                client_side_key="environment_key",
-            )
-        ]
-    )
+    environment_key_pairs: list[EnvironmentKeyPair]
     api_url: HttpUrl = HttpUrl("https://edge.api.flagsmith.com/api/v1")
     api_poll_frequency_seconds: int = Field(
         default=10,
diff --git a/tests/conftest.py b/tests/conftest.py
index 9a2df0f..1cf2cfd 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -51,8 +51,15 @@ def environment_1_feature_states_response_list_response_with_identity_override(
 
 
 @pytest.fixture(autouse=True)
-def skip_json_config_settings_source(mocker: MockerFixture) -> None:
-    mocker.patch("edge_proxy.settings.json_config_settings_source", dict)
+def mock_settings(mocker: MockerFixture) -> None:
+    mock_config = {
+        "environment_key_pairs": [
+            {"server_side_key": "ser.abc123", "client_side_key": "def456"}
+        ]
+    }
+    mocker.patch(
+        "edge_proxy.settings.json_config_settings_source", return_value=mock_config
+    )
 
 
 @pytest.fixture
diff --git a/tests/test_server.py b/tests/test_server.py
index 3f5d19e..0a19985 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -6,7 +6,7 @@
 from fastapi.testclient import TestClient
 from pytest_mock import MockerFixture
 
-from edge_proxy.settings import AppSettings, HealthCheckSettings
+from edge_proxy.settings import HealthCheckSettings
 from tests.fixtures.response_data import environment_1
 
 if typing.TYPE_CHECKING:
@@ -59,10 +59,8 @@ def test_health_check_returns_200_if_cache_is_stale_and_health_check_configured_
     client: TestClient,
 ) -> None:
     # Given
-    settings = AppSettings(
-        health_check=HealthCheckSettings(environment_update_grace_period_seconds=None)
-    )
-    mocker.patch("edge_proxy.server.settings", settings)
+    health_check = HealthCheckSettings(environment_update_grace_period_seconds=None)
+    mocker.patch("edge_proxy.server.settings.health_check", health_check)
 
     last_updated_at = datetime.now() - timedelta(days=10)
     mocked_environment_service = mocker.patch("edge_proxy.server.environment_service")
diff --git a/tests/test_settings.py b/tests/test_settings.py
index d649002..d99f2d0 100644
--- a/tests/test_settings.py
+++ b/tests/test_settings.py
@@ -1,9 +1,32 @@
-import typing
+from typing import Any, Optional
 
 import pytest
 from pytest_mock import MockerFixture
+from pydantic import ValidationError
 
-from edge_proxy.settings import get_settings
+from edge_proxy.settings import get_settings, AppSettings
+
+
+@pytest.mark.parametrize(
+    "client_side_key,server_side_key,expected_exception",
+    [
+        ("abc123", "ser.456", None),
+        ("abc123", "456", ValidationError),
+        ("abc123", "", ValidationError),
+        ("", "ser.456", ValidationError),
+    ],
+)
+def test_client_side_key_validation(
+    client_side_key: str, server_side_key: str, expected_exception: Optional[Exception]
+) -> None:
+    try:
+        AppSettings(
+            environment_key_pairs=[
+                {"server_side_key": server_side_key, "client_side_key": client_side_key}
+            ]
+        )
+    except expected_exception:
+        pass
 
 
 @pytest.mark.parametrize(
@@ -12,7 +35,7 @@
         (
             {
                 "environment_key_pairs": [
-                    {"server_side_key": "abc123", "client_side_key": "ser.def456"}
+                    {"server_side_key": "ser.abc123", "client_side_key": "def456"}
                 ],
                 "api_poll_frequency": 10,
                 "api_poll_timeout": 10,
@@ -23,7 +46,7 @@
         (
             {
                 "environment_key_pairs": [
-                    {"server_side_key": "abc123", "client_side_key": "ser.def456"}
+                    {"server_side_key": "ser.abc123", "client_side_key": "def456"}
                 ],
                 "api_poll_frequency_seconds": 10,
                 "api_poll_timeout_seconds": 10,
@@ -35,8 +58,8 @@
 )
 def test_settings_are_loaded_correctly(
     mocker: MockerFixture,
-    config_file_json: dict[str, typing.Any],
-    expected_config: dict[str, typing.Any],
+    config_file_json: dict[str, Any],
+    expected_config: dict[str, Any],
 ) -> None:
     """
     Parametrized test which accepts a raw json config file, and a dictionary representing the