diff --git a/ventures/havre/tools/open.sh b/ventures/havre/tools/open.sh
new file mode 100644
index 0000000..74efd73
--- /dev/null
+++ b/ventures/havre/tools/open.sh
@@ -0,0 +1,18 @@
+#!/bin/sh
+# tools/open.sh: build openvenice (https://github.com/nikshepsvn/openvenice, MIT) into open/, served at /open/.
+# Pinned to one commit; bump OV_REF to take a newer one. Run by tools/build.sh. Needs git, node 20+ and npm.
+set -eu
+cd "$(dirname "$0")/.."
+OV_REF=d983874a79810edaffb85721911630af29d09d95
+src=$(mktemp -d)
+git clone -q https://github.com/nikshepsvn/openvenice "$src"
+git -C "$src" checkout -q "$OV_REF"
+(cd "$src" && npm ci --silent --no-audit --no-fund >/dev/null && npx vite build --base=/open/ >/dev/null)
+rm -rf open
+cp -R "$src/dist" open
+cat > open/LICENSE.txt <<EOF
+openvenice by nikshepsvn, MIT License: https://github.com/nikshepsvn/openvenice
+Built into Havre at /open/ from commit $OV_REF, unchanged.
+EOF
+rm -rf "$src"
+echo "open/: openvenice @ $OV_REF ($(find open -type f | wc -l | tr -d ' ') files)"