diff --git a/datareservoirio/environments.py b/datareservoirio/environments.py
index f6703fdb..ace6c6e0 100644
--- a/datareservoirio/environments.py
+++ b/datareservoirio/environments.py
@@ -43,6 +43,29 @@ def set_dev(self):
             _constants.APPLICATIONINSIGHTS_DEV_CONNECTIONSTRING
         )
 
+    def set_api_base_url(self, base_url):
+        """
+        Point the client at a custom DataReservoir.io API base URL.
+
+        Intended for development/testing against a mock server. The
+        environment is marked as DEV, so telemetry (if explicitly enabled)
+        uses the DEV config and does not leak to the production resource.
+
+        Parameters
+        ----------
+        base_url : str
+            Full API base URL including the ``/api/`` suffix, e.g.
+            ``"http://localhost:5824/api/"``. A trailing slash is added if
+            missing.
+        """
+        if not base_url.endswith("/"):
+            base_url = base_url + "/"
+        self._set_environment(_constants.ENV_DEV)
+        self._set_base_url(base_url)
+        self._set_application_insight_connectionstring(
+            _constants.APPLICATIONINSIGHTS_DEV_CONNECTIONSTRING
+        )
+
     def _set_environment(self, environment):
         self._logger.info(f"Setting environment to: {environment}")
         self.current_environment = environment
diff --git a/tests/test_environments.py b/tests/test_environments.py
index f3cce035..b38f1e2e 100644
--- a/tests/test_environments.py
+++ b/tests/test_environments.py
@@ -75,6 +75,19 @@ def test_set_dev(self, environment):
             == _constants.APPLICATIONINSIGHTS_DEV_CONNECTIONSTRING
         )
 
+    def test_set_api_base_url(self, environment):
+        environment.set_api_base_url("http://drio-mock.gov:1337/api/")
+        assert environment.current_environment == "DEV"
+        assert environment.api_base_url == "http://drio-mock.gov:1337/api/"
+        assert (
+            environment._application_insight_connectionstring
+            == _constants.APPLICATIONINSIGHTS_DEV_CONNECTIONSTRING
+        )
+
+    def test_set_api_base_url_adds_trailing_slash(self, environment):
+        environment.set_api_base_url("http://localhost:42/api")
+        assert environment.api_base_url == "http://localhost:42/api/"
+
     def test__set_environment(self, environment):
         environment._set_environment("QA")
         assert environment.current_environment == "QA"