diff --git a/tools/viscompare.sh b/tools/viscompare.sh
new file mode 100755
index 0000000..cbc273d
--- /dev/null
+++ b/tools/viscompare.sh
@@ -0,0 +1,25 @@
+#!/bin/sh
+#
+# Visually compare the dot files reported as different when running
+# the test.
+#
+# Specify as an argument the name of the file reported as different.
+# Example: viscompare.sh Category.dot
+# Example2: for i in `cd dot-ref ; ls *.dot`; do ../viscompare.sh $i; done
+#
+# $Id$
+#
+
+filea=`find . -name $1 | sed -n 1p`
+fileb=`find . -name $1 | sed -n 2p`
+diff $filea $fileb
+echo left $filea - right $fileb
+dot -Tpng $filea | pngtopnm >a.pnm
+dot -Tpng $fileb | pngtopnm >b.pnm
+pnmcat -lr a.pnm b.pnm | pnmtopng >comp.png
+
+start comp.png		# Windows-specific
+
+echo -n Press enter to finish
+read dummy
+rm -f a.pnm b.pnm comp.png