diff --git a/server.js b/server.js
index 620ebda..c611fd8 100644
--- a/server.js
+++ b/server.js
@@ -4,6 +4,8 @@ const path = require('path');
 
 const ROOT = __dirname;
 const DATA_FILE = path.join(ROOT, 'data.json');
+const BACKUP_DIR = process.env.BPI_BACKUP_DIR || path.join(ROOT, 'backups');
+const MAX_BACKUPS = Number(process.env.BPI_MAX_BACKUPS) || 100;
 const PORT = Number(process.env.PORT) || 8080;
 
 const TYPES = {
@@ -34,6 +36,34 @@ function readBody(req) {
   });
 }
 
+function timestamp() {
+  return new Date().toISOString().replace(/[:.]/g, '-');
+}
+
+function backupDataFile() {
+  if (!fs.existsSync(DATA_FILE)) return null;
+
+  fs.mkdirSync(BACKUP_DIR, { recursive: true });
+  const backupFile = path.join(BACKUP_DIR, `data-${timestamp()}.json`);
+  fs.copyFileSync(DATA_FILE, backupFile);
+
+  const backups = fs
+    .readdirSync(BACKUP_DIR)
+    .filter((name) => /^data-.*\.json$/.test(name))
+    .map((name) => ({
+      name,
+      file: path.join(BACKUP_DIR, name),
+      mtime: fs.statSync(path.join(BACKUP_DIR, name)).mtimeMs,
+    }))
+    .sort((a, b) => b.mtime - a.mtime);
+
+  for (const oldBackup of backups.slice(MAX_BACKUPS)) {
+    fs.rmSync(oldBackup.file, { force: true });
+  }
+
+  return backupFile;
+}
+
 const server = http.createServer(async (req, res) => {
   try {
     const url = new URL(req.url, `http://${req.headers.host}`);
@@ -46,8 +76,9 @@ const server = http.createServer(async (req, res) => {
         return send(res, 400, JSON.stringify({ error: 'Invalid data format' }), 'application/json; charset=utf-8');
       }
 
+      const backupFile = backupDataFile();
       fs.writeFileSync(DATA_FILE, JSON.stringify(data, null, 2) + '\n');
-      return send(res, 200, JSON.stringify({ ok: true }), 'application/json; charset=utf-8');
+      return send(res, 200, JSON.stringify({ ok: true, backup: backupFile ? path.basename(backupFile) : null }), 'application/json; charset=utf-8');
     }
 
     if (req.method !== 'GET' && req.method !== 'HEAD') {