diff --git a/tools/makefile b/tools/makefile
index 2ffc923..32bbdd5 100644
--- a/tools/makefile
+++ b/tools/makefile
@@ -15,7 +15,7 @@ cmd_cp := cp
 ## rules
 
 .PHONY: default
-default: ${dir_build}/logic.js ${dir_build}/style.css ${dir_build}/index.html
+default: ${dir_build}/logic.js ${dir_build}/style.css ${dir_build}/index.html data
 
 ${dir_temp}/logic-unlinked.js: \
 	${dir_lib}/plankton/plankton.d.ts \
@@ -67,3 +67,9 @@ ${dir_build}/index.html: \
 	@ ${cmd_log} "structure …"
 	@ ${cmd_mkdir} $(dir $@)
 	@ tools/make-index $^ > $@
+
+.PHONY: data
+data:
+	@ ${cmd_log} "data …"
+	@ ${cmd_mkdir} ${dir_build}/data
+	@ ${cmd_cp} -r -u -v ${dir_source}/data/* ${dir_build}/data/