diff --git a/Dockerfile b/Dockerfile
index f945e77..010da86 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -57,8 +57,14 @@ COPY css/ /usr/share/nginx/html/css/
 RUN mkdir -p /data && chown nginx:nginx /data
 VOLUME /data
 
+# Copy and set up entrypoint script
+COPY entrypoint.sh /usr/local/bin/entrypoint.sh
+RUN chmod +x /usr/local/bin/entrypoint.sh
+
+ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]
+
 # Expose port 80 for Nginx
 EXPOSE 80
 
-# Start Supervisor
+# Start Supervisor (this will be passed to entrypoint.sh)
 CMD ["/usr/bin/supervisord", "-c", "/etc/supervisor/conf.d/supervisord.conf"]
diff --git a/entrypoint.sh b/entrypoint.sh
new file mode 100644
index 0000000..473d021
--- /dev/null
+++ b/entrypoint.sh
@@ -0,0 +1,40 @@
+#!/bin/sh
+# entrypoint.sh
+
+set -e # Exit immediately if a command exits with a non-zero status.
+
+DATA_FILE_PATH="/data/weight-tracker-data.json"
+DATA_DIR="/data"
+APP_USER="nginx" # This should match the user set in supervisord.conf for your Node.js app
+
+# 1. Ensure the data directory exists and is owned by APP_USER.
+#    The -p flag for mkdir ensures it doesn't error if the directory already exists.
+if ! mkdir -p "${DATA_DIR}"; then
+    echo "Error: Could not create data directory ${DATA_DIR}. Exiting."
+    exit 1
+fi
+
+if ! chown "${APP_USER}:${APP_USER}" "${DATA_DIR}"; then
+    echo "Error: Could not set ownership of ${DATA_DIR} to ${APP_USER}. Exiting."
+    # This might happen if the volume is mounted with very restrictive host permissions.
+    # For now, we'll try to proceed, as the file chown might still work or be more critical.
+    # Consider exiting 1 here if directory ownership is strictly required for other reasons.
+fi
+
+# 2. Ensure the data file itself is writable by APP_USER.
+#    Touching it creates it if it doesn't exist.
+#    Chowning it ensures the correct user owns it, even if it pre-existed with root ownership from a volume mount.
+if ! touch "${DATA_FILE_PATH}"; then
+    echo "Error: Could not touch/create data file ${DATA_FILE_PATH}. Exiting."
+    exit 1
+fi
+
+if ! chown "${APP_USER}:${APP_USER}" "${DATA_FILE_PATH}"; then
+    echo "Error: Could not set ownership of ${DATA_FILE_PATH} to ${APP_USER}. Exiting."
+    exit 1
+fi
+
+echo "Entrypoint: Permissions for ${DATA_FILE_PATH} set for user ${APP_USER}."
+
+# 3. Execute the main command passed to this script (e.g., supervisord)
+exec "$@"