diff --git a/src/common.h b/src/common.h
index a4f03a7..57397fa 100644
--- a/src/common.h
+++ b/src/common.h
@@ -16,4 +16,12 @@ uint32_t makeip4(int, int, int, int);
 /* Reads a stream into a buffer until end of line */
 int readline(int, char*, int);
 
+/* Protocol command definitions */
+#define CMD_HELLO 'H'
+#define CMD_HELP 'h'
+#define CMD_QUIT 'q'
+#define CMD_SEND_MESSAGE 's'
+#define CMD_BROADCAST 'b'
+#define CMD_LIST_CONNECTED 'l'
+
 #endif