diff --git a/tools/hmac.ts b/tools/hmac.ts
new file mode 100644
index 0000000..9a303f0
--- /dev/null
+++ b/tools/hmac.ts
@@ -0,0 +1,22 @@
+import crypto from 'crypto'
+import fs from 'fs'
+
+const hmacKey = crypto.randomBytes(32).toString('hex')
+
+if (fs.existsSync('.env.local')) {
+  const envFile = fs.readFileSync('.env.local', 'utf8')
+  // Double-check it's not already set
+  if (!envFile.includes('ALTCHA_SECRETKEY')) {
+    fs.appendFileSync('.env.local', `\nALTCHA_SECRETKEY=${hmacKey}`)
+  }
+  console.log(`Successfully wrote ALTCHA_SECRETKEY to .env.local`)
+} else if (fs.existsSync('.env')) {
+  const envFile = fs.readFileSync('.env', 'utf8')
+  // Double-check it's not already set
+  if (!envFile.includes('ALTCHA_SECRETKEY')) {
+    fs.appendFileSync('.env', `\nALTCHA_SECRETKEY=${hmacKey}`)
+  }
+  console.log(`Successfully wrote ALTCHA_SECRETKEY to .env`)
+} else {
+  console.error('No .env/.env.local file found, please create one first.')
+}
\ No newline at end of file