diff --git a/app/Rules/Webfinger.php b/app/Rules/Webfinger.php
new file mode 100644
index 000000000..e91fb9e5e
--- /dev/null
+++ b/app/Rules/Webfinger.php
@@ -0,0 +1,62 @@
+<?php
+
+namespace App\Rules;
+
+use Illuminate\Contracts\Validation\Rule;
+
+class WebFinger implements Rule
+{
+    /**
+     * Determine if the validation rule passes.
+     *
+     * @param  string  $attribute
+     * @param  mixed  $value
+     * @return bool
+     */
+    public function passes($attribute, $value)
+    {
+        if (! is_string($value)) {
+            return false;
+        }
+
+        $mention = $value;
+        if (str_starts_with($mention, '@')) {
+            $mention = substr($mention, 1);
+        }
+
+        $parts = explode('@', $mention);
+        if (count($parts) !== 2) {
+            return false;
+        }
+
+        [$username, $domain] = $parts;
+
+        if (empty($username) ||
+            ! preg_match('/^[a-zA-Z0-9_.-]+$/', $username) ||
+            strlen($username) >= 80) {
+            return false;
+        }
+
+        if (empty($domain) ||
+            ! str_contains($domain, '.') ||
+            ! preg_match('/^[a-zA-Z0-9.-]+$/', $domain) ||
+            strlen($domain) >= 255) {
+            return false;
+        }
+
+        // Optional: Check if domain resolves (can be enabled for stricter validation)
+        // return checkdnsrr($domain, 'A') || checkdnsrr($domain, 'AAAA') || checkdnsrr($domain, 'MX');
+
+        return true;
+    }
+
+    /**
+     * Get the validation error message.
+     *
+     * @return string
+     */
+    public function message()
+    {
+        return 'The :attribute must be a valid WebFinger address (username@domain.tld or @username@domain.tld)';
+    }
+}