diff --git a/GameEngine/Instance/ConfigWriter.php b/GameEngine/Instance/ConfigWriter.php
new file mode 100644
index 00000000..e80770fd
--- /dev/null
+++ b/GameEngine/Instance/ConfigWriter.php
@@ -0,0 +1,50 @@
+<?php
+
+/**
+ * Writes an isolated TravianZ instance configuration from the normal
+ * constant_format.tpl template.
+ *
+ * The writer deliberately works with an explicit replacement map. This keeps
+ * the existing installer semantics intact and, importantly, preserves every
+ * comment and line from the canonical template.
+ */
+class TravianZInstanceConfigWriter
+{
+    public static function write($instanceId, array $replacements)
+    {
+        $instanceId = TravianZInstance::sanitizeId($instanceId);
+        $instancePath = TravianZInstance::path($instanceId);
+        $sourceTemplate = dirname(__DIR__) . '/../install/data/constant_format.tpl';
+
+        if (!is_file($sourceTemplate)) {
+            throw new RuntimeException('Installer configuration template not found.');
+        }
+
+        if (!is_dir($instancePath) && !mkdir($instancePath, 0775, true) && !is_dir($instancePath)) {
+            throw new RuntimeException('Cannot create instance directory: ' . $instanceId);
+        }
+
+        $text = file_get_contents($sourceTemplate);
+        if ($text === false) {
+            throw new RuntimeException('Cannot read installer configuration template.');
+        }
+
+        if ($replacements) {
+            $text = str_replace(array_keys($replacements), array_values($replacements), $text);
+        }
+
+        $configPath = $instancePath . '/config.php';
+        $tmpPath = $configPath . '.tmp';
+
+        if (file_put_contents($tmpPath, $text, LOCK_EX) === false) {
+            throw new RuntimeException('Cannot write temporary instance configuration.');
+        }
+
+        if (!rename($tmpPath, $configPath)) {
+            @unlink($tmpPath);
+            throw new RuntimeException('Cannot activate instance configuration.');
+        }
+
+        return $configPath;
+    }
+}