diff --git a/connector_builder_mcp/validation_testing.py b/connector_builder_mcp/validation_testing.py
index 52ed3dd..97bc80a 100644
--- a/connector_builder_mcp/validation_testing.py
+++ b/connector_builder_mcp/validation_testing.py
@@ -566,6 +566,16 @@ def run_connector_readiness_test_report(  # noqa: PLR0912, PLR0914, PLR0915 (too
     if isinstance(streams, str):
         stream_names = [s.strip() for s in streams.split(",") if s.strip()]
     else:
+        if available_streams:
+            invalid_streams = [s for s in available_streams if not isinstance(s, dict)]
+            if invalid_streams:
+                raise ValueError(
+                    f"Invalid manifest structure: 'streams' must be a list of stream definition objects (dicts), "
+                    f"but found {len(invalid_streams)} invalid entry(ies). "
+                    f"Each stream should be an object with at least a 'name' field and stream configuration. "
+                    f"Invalid entries: {invalid_streams[:3]}"
+                )
+
         stream_names = [
             stream.get("name", f"stream_{i}") for i, stream in enumerate(available_streams)
         ]
diff --git a/tests/integration/test_validation_and_testing.py b/tests/integration/test_validation_and_testing.py
index f043d66..df333ac 100644
--- a/tests/integration/test_validation_and_testing.py
+++ b/tests/integration/test_validation_and_testing.py
@@ -174,6 +174,32 @@ def test_simple_api_manifest_workflow(simple_api_manifest_yaml) -> None:
     assert "streams" in resolved_manifest
 
 
+def test_malformed_manifest_streams_validation() -> None:
+    """Test that malformed manifest with streams as list of strings raises clear error."""
+    malformed_manifest = """
+version: 4.6.2
+type: DeclarativeSource
+check:
+  type: CheckStream
+  stream_names:
+    - test_stream
+streams:
+  - test_stream
+  - another_stream
+spec:
+  type: Spec
+  connection_specification:
+    type: object
+    properties: {}
+"""
+
+    with pytest.raises(
+        ValueError,
+        match=r"Invalid manifest structure.*streams.*must be a list of stream definition objects",
+    ):
+        run_connector_readiness_test_report(manifest=malformed_manifest, config={}, max_records=5)
+
+
 @pytest.mark.parametrize(
     "manifest_fixture,stream_name",
     [