diff --git a/publishing/build.sh b/publishing/build.sh
index de2f8bd..0e49dfa 100755
--- a/publishing/build.sh
+++ b/publishing/build.sh
@@ -41,6 +41,9 @@ tar cf - \
   --exclude='requirements.txt' \
   . | tar xf - -C "$SITE_SRC"
 
+# A file that must sit at the site root (crawler rules), not under publishing/.
+cp publishing/robots.txt "$SITE_SRC/robots.txt"
+
 # 2. Build.
 if [ ! -x "$VENV/bin/mkdocs" ]; then
   echo "Creating build venv at $VENV"
diff --git a/publishing/robots.txt b/publishing/robots.txt
new file mode 100644
index 0000000..0840e54
--- /dev/null
+++ b/publishing/robots.txt
@@ -0,0 +1,3 @@
+# Documentation site crawler rules
+User-agent: *
+Allow: /