diff --git a/src/Util/NostrKeyUtil.php b/src/Util/NostrKeyUtil.php
new file mode 100644
index 0000000..09ccfc6
--- /dev/null
+++ b/src/Util/NostrKeyUtil.php
@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Util;
+
+use swentel\nostr\Key\Key;
+
+class NostrKeyUtil
+{
+    /**
+     * Check if a string is a valid hex pubkey (64 hex chars).
+     */
+    public static function isHexPubkey(string $pubkey): bool
+    {
+        return (bool) preg_match('/^[a-fA-F0-9]{64}$/', $pubkey);
+    }
+
+    /**
+     * Check if a string is a valid bech32 npub (starts with npub1).
+     */
+    public static function isNpub(string $npub): bool
+    {
+        return str_starts_with($npub, 'npub1');
+    }
+
+    /**
+     * Convert npub (bech32) to hex pubkey.
+     * Throws \InvalidArgumentException if invalid.
+     */
+    public static function npubToHex(string $npub): string
+    {
+        if (!self::isNpub($npub)) {
+            throw new \InvalidArgumentException('Not a valid npub');
+        }
+        $key = new Key();
+        return $key->convertToHex($npub);
+    }
+
+    /**
+     * Convert hex pubkey to npub (bech32).
+     * Throws \InvalidArgumentException if invalid.
+     */
+    public static function hexToNpub(string $pubkey): string
+    {
+        if (!self::isHexPubkey($pubkey)) {
+            throw new \InvalidArgumentException('Not a valid hex pubkey');
+        }
+        $key = new Key();
+        return $key->convertPublicKeyToBech32($pubkey);
+    }
+}
+