diff --git a/contrib/cov-diff b/contrib/cov-diff
new file mode 100755
index 0000000000000000000000000000000000000000..33a54802b6004ff44bdb324c5f0b650f23d0fbb4
--- /dev/null
+++ b/contrib/cov-diff
@@ -0,0 +1,17 @@
+#!/bin/sh
+# Copyright 2013  The Tor Project, Inc.
+# See LICENSE for licensing information.
+
+# cov-diff -- compare two directories full of gcov files.
+
+DIRA="$1"
+DIRB="$2"
+
+for A in $DIRA/*; do
+  B=$DIRB/`basename $A`
+  perl -pe 's/^\s*\d+:/        1:/; s/^([^:]+:)[\d\s]+:/$1/;' "$A" > "$A.tmp"
+  perl -pe 's/^\s*\d+:/        1:/; s/^([^:]+:)[\d\s]+:/$1/;' "$B" > "$B.tmp"
+  diff -u "$A.tmp" "$B.tmp"
+  rm "$A.tmp" "$B.tmp"
+done
+