diff --git a/sdk/core/azure-core/CHANGELOG.md b/sdk/core/azure-core/CHANGELOG.md
index ca1427a75ab2..3e2a871b735d 100644
--- a/sdk/core/azure-core/CHANGELOG.md
+++ b/sdk/core/azure-core/CHANGELOG.md
@@ -6,6 +6,7 @@
 ### Bug fixes
 
 - `AzureKeyCredentialPolicy` will now accept (and ignore) passed in kwargs  #11963
+- Better error messages if passed endpoint is incorrect  #12106
 
 ## 1.6.0 (2020-06-03)
 
diff --git a/sdk/core/azure-core/azure/core/pipeline/transport/_base.py b/sdk/core/azure-core/azure/core/pipeline/transport/_base.py
index d6e14b4f6876..f7e83aed4460 100644
--- a/sdk/core/azure-core/azure/core/pipeline/transport/_base.py
+++ b/sdk/core/azure-core/azure/core/pipeline/transport/_base.py
@@ -112,6 +112,18 @@ def _case_insensitive_dict(*args, **kwargs):
 
 
 def _format_url_section(template, **kwargs):
+    """String format the template with the kwargs, auto-skip sections of the template that are NOT in the kwargs.
+
+    By default in Python, "format" will raise a KeyError if a template element is not found. Here the section between
+    the slashes will be removed from the template instead.
+
+    This is used for API like Storage, where when Swagger has template section not defined as parameter.
+
+    :param str template: a string template to fill
+    :param dict[str,str] kwargs: Template values as string
+    :rtype: str
+    :returns: Template completed
+    """
     components = template.split("/")
     while components:
         try:
@@ -718,7 +730,12 @@ def format_url(self, url_template, **kwargs):
             parsed = urlparse(url)
             if not parsed.scheme or not parsed.netloc:
                 url = url.lstrip("/")
-                base = self._base_url.format(**kwargs).rstrip("/")
+                try:
+                    base = self._base_url.format(**kwargs).rstrip("/")
+                except KeyError as key:
+                    err_msg = "The value provided for the url part {} was incorrect, and resulted in an invalid url"
+                    raise ValueError(err_msg.format(key.args[0]))
+
                 url = _urljoin(base, url)
         else:
             url = self._base_url.format(**kwargs)
diff --git a/sdk/core/azure-core/tests/test_pipeline.py b/sdk/core/azure-core/tests/test_pipeline.py
index c2fa56b0379e..bbbd37c09f5e 100644
--- a/sdk/core/azure-core/tests/test_pipeline.py
+++ b/sdk/core/azure-core/tests/test_pipeline.py
@@ -204,6 +204,12 @@ def test_format_url_no_base_url(self):
         formatted = client.format_url("https://google.com/subpath/{foo}", foo="bar")
         assert formatted == "https://google.com/subpath/bar"
 
+    def test_format_incorrect_endpoint(self):
+        # https://github.com/Azure/azure-sdk-for-python/pull/12106
+        client = PipelineClientBase('{Endpoint}/text/analytics/v3.0')
+        with pytest.raises(ValueError) as exp:
+            client.format_url("foo/bar")
+        assert str(exp.value) == "The value provided for the url part Endpoint was incorrect, and resulted in an invalid url"
 
 class TestClientRequest(unittest.TestCase):
     def test_request_json(self):