diff --git a/src/app/subagent/division.rs b/src/app/subagent/division.rs
index c2da0b9..5f39672 100644
--- a/src/app/subagent/division.rs
+++ b/src/app/subagent/division.rs
@@ -88,4 +88,14 @@ mod tests {
         assert!(!tools.contains(&"write".to_string()));
         assert!(!tools.contains(&"delete".to_string()));
     }
+
+    #[test]
+    fn read_tier_is_subset_of_write_tier_and_write_is_subset_of_full() {
+        use std::collections::HashSet;
+        let read: HashSet<_> = tools_for(READ).into_iter().collect();
+        let write: HashSet<_> = tools_for(WRITE).into_iter().collect();
+        let full: HashSet<_> = tools_for(FULL).into_iter().collect();
+        assert!(read.is_subset(&write), "read tier must be a subset of write tier");
+        assert!(write.is_subset(&full), "write tier must be a subset of full tier");
+    }
 }