diff --git a/prophet/domain/improvement_repo.py b/prophet/domain/improvement_repo.py
new file mode 100644
index 0000000..57e7083
--- /dev/null
+++ b/prophet/domain/improvement_repo.py
@@ -0,0 +1,15 @@
+
+from typing import Protocol
+
+from prophet.domain.improvement import Improvement
+
+
+class IImprovementRepo(Protocol):
+    def add(self, improvement: Improvement) -> None:
+        raise NotImplementedError
+
+    def get(self, id: str) -> Improvement:
+        raise NotImplementedError
+
+    def get_all(self) -> list[Improvement]:
+        raise NotImplementedError