diff --git a/devtools/unused-functions.sh b/devtools/unused-functions.sh
new file mode 100755
index 000000000..447935467
--- /dev/null
+++ b/devtools/unused-functions.sh
@@ -0,0 +1,30 @@
+#! /bin/sh
+
+# Files to look inside: don't count test files.  We don't use git grep
+# because we want to find occurences in wiregen files.
+FILES=$(find ./* -name '*.[ch]' | grep -v /test/run- | grep -v ^./ccan/ | grep -v ^./external/ | grep -v ^./tests/)
+
+if [ $# = 0 ]; then
+    HEADERS=$(echo [a-z]*/*.h)
+else
+    HEADERS="$*"
+fi
+
+for hfile in $HEADERS; do
+    # Don't worry about wiregen unused functions.
+    if [ "${hfile%_wiregen.h}" != "${hfile}" ]; then
+	continue
+    fi
+    # shellcheck disable=SC2010 disable=SC2086
+    USING=$(ls $FILES | grep -v "^./${hfile%.h}\.")
+    funcs=$(sed -n 's/^[^#].* \**\([a-z0-9_]*\)(.*/\1/p;s/^\([a-z0-9_]*\)(.*/\1/p' < "$hfile")
+    for f in $funcs; do
+	# Ignore C and H files both: don't use git grep since we want to find
+	# occurrences in generated files too.
+	# echo Looking through $(echo $FILES | grep -v "^${hfile%.h}\.")
+	# shellcheck disable=SC2086
+	if ! grep -qw $f $USING; then
+	    echo "$(grep -nHw "$f" "$hfile" | head -n1)": "$f" unused
+	fi
+    done
+done