diff --git a/solitaire_engine/src/platform/storage.rs b/solitaire_engine/src/platform/storage.rs
index d9d2097..9dca2f2 100644
--- a/solitaire_engine/src/platform/storage.rs
+++ b/solitaire_engine/src/platform/storage.rs
@@ -1,3 +1,8 @@
+//! Platform-specific persistent storage backends.
+//!
+//! Native builds persist bytes under the app data directory, while browser
+//! builds route the same engine API through `localStorage`.
+
 use std::io;
 use std::sync::Arc;
 
diff --git a/solitaire_engine/src/platform/time.rs b/solitaire_engine/src/platform/time.rs
index c7492d3..8a6b49e 100644
--- a/solitaire_engine/src/platform/time.rs
+++ b/solitaire_engine/src/platform/time.rs
@@ -1,3 +1,5 @@
+//! Platform-specific wall-clock time sources.
+
 /// Abstracts platform-specific wall-clock time.
 ///
 /// Native: backed by `std::time::SystemTime`.