diff --git a/src/cal_tools/warnings.py b/src/cal_tools/warnings.py
new file mode 100644
index 0000000000000000000000000000000000000000..10b1c2df833bea8441b1134b2147f12335ff18ec
--- /dev/null
+++ b/src/cal_tools/warnings.py
@@ -0,0 +1,2 @@
+class CalWarning(UserWarning):
+    pass
\ No newline at end of file