diff --git a/autoemulate/metrics.py b/autoemulate/metrics.py
index c062019a..5903593f 100644
--- a/autoemulate/metrics.py
+++ b/autoemulate/metrics.py
@@ -29,6 +29,7 @@ def r2(y_true, y_pred):
     return r2_score(y_true, y_pred)
 
 
+#: A dictionary of available metrics.
 METRIC_REGISTRY = {
     "rmse": rmse,
     "r2": r2,