diff --git a/tools/gen_api_header.sh b/tools/gen_api_header.sh
new file mode 100755
index 0000000..2b21995
--- /dev/null
+++ b/tools/gen_api_header.sh
@@ -0,0 +1,4 @@
+#!/bin/env sh
+# single header api generator with clang
+
+clang -I./ -P -E -nostdinc -nobuiltininc -DTWN_NOT_C $TWNROOT/include/twn_game_api.h | clang-format
diff --git a/tools/twn b/tools/twn
index bc0d6c5..c8bb124 100755
--- a/tools/twn
+++ b/tools/twn
@@ -36,6 +36,9 @@ case "$1" in
     esac
                ;;
 
+    api-gen  ) "$toolpath"/gen_api_header.sh
+               ;;
+
     *        ) echo "Unknown command."
                ;;
 esac