diff --git a/quic/platform/api/quic_clock.h b/quic/platform/api/quic_clock.h
index afd82dc..8000017 100644
--- a/quic/platform/api/quic_clock.h
+++ b/quic/platform/api/quic_clock.h
@@ -8,6 +8,11 @@
 #include "net/third_party/quiche/src/quic/core/quic_time.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_export.h"
 
+/* API_DESCRIPTION
+ QuicClock is used by QUIC core to get current time. Its instance is created by
+ applications and passed into QuicDispatcher and QuicConnectionHelperInterface.
+ API-DESCRIPTION */
+
 namespace quic {
 
 // Interface for retrieving the current time.
diff --git a/quic/platform/api/quic_mem_slice.h b/quic/platform/api/quic_mem_slice.h
index a4318ad..bcc7123 100644
--- a/quic/platform/api/quic_mem_slice.h
+++ b/quic/platform/api/quic_mem_slice.h
@@ -8,6 +8,13 @@
 #include "net/third_party/quiche/src/quic/platform/api/quic_export.h"
 #include "net/quic/platform/impl/quic_mem_slice_impl.h"
 
+/* API_DESCRIPTION
+ QuicMemSlice is used to wrap application data and pass to QUIC stream's write
+ interface. It refers to a memory block of data which should be around till
+ QuicMemSlice::Reset() is called. It's upto each platform, to implement it as
+ reference counted or not.
+ API-DESCRIPTION */
+
 namespace quic {
 
 // QuicMemSlice is an internally reference counted data buffer used as the