diff --git a/install/process_instance.php b/install/process_instance.php
new file mode 100644
index 00000000..72ff1795
--- /dev/null
+++ b/install/process_instance.php
@@ -0,0 +1,367 @@
+<?php
+
+#################################################################################
+##              -= YOU MAY NOT REMOVE OR CHANGE THIS NOTICE =-                 ##
+## --------------------------------------------------------------------------- ##
+##  Project:       TravianZ                                                    ##
+##  Filename       process_instance.php                                        ##
+##  Type           : Multi-instance installation process                       ##
+##  Project        : TravianZ                                                  ##
+##  Source code    : https://github.com/Shadowss/TravianZ                     ##
+#################################################################################
+
+// don't let SQL time out when 30-500 seconds (depending on php.ini) is not enough
+@set_time_limit(0);
+
+require_once dirname(__DIR__) . '/GameEngine/Instance/InstanceResolver.php';
+require_once dirname(__DIR__) . '/GameEngine/Instance/Instance.php';
+require_once dirname(__DIR__) . '/GameEngine/Instance/ConfigRouter.php';
+require_once dirname(__DIR__) . '/GameEngine/Instance/ConfigWriter.php';
+
+final class TravianZInstanceInstallProcess
+{
+    private string $root;
+    private string $instancesFile;
+
+    public function __construct()
+    {
+        $this->root = dirname(__DIR__);
+        $this->instancesFile = $this->root . '/instances/registry.json';
+    }
+
+    public function run(): void
+    {
+        if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
+            $this->fail('Invalid request method.');
+        }
+
+        $instanceId = strtolower(trim((string) ($_POST['instance_id'] ?? '')));
+        if (!TravianZInstanceResolver::isValid($instanceId)) {
+            $this->fail('Invalid instance ID.');
+        }
+
+        // Select this instance before Bootstrap/Database are loaded.
+        putenv('TRAVIANZ_INSTANCE=' . $instanceId);
+
+        $action = (string) ($_POST['action'] ?? 'config');
+
+        try {
+            switch ($action) {
+                case 'config':
+                    $this->writeConfig($instanceId);
+                    break;
+
+                case 'structure':
+                    $this->loadInstanceBootstrap();
+                    $this->createStructure($instanceId);
+                    break;
+
+                case 'world':
+                    $this->loadInstanceBootstrap();
+                    $this->createWorld($instanceId);
+                    break;
+
+                case 'finalize':
+                    $this->finalize($instanceId);
+                    break;
+
+                default:
+                    $this->fail('Unknown installation action.');
+            }
+        } catch (Throwable $e) {
+            $this->fail($e->getMessage());
+        }
+    }
+
+    /**
+     * Converts the existing installer POST fields into the placeholders used
+     * by constant_format.tpl. This deliberately mirrors the normal installer
+     * naming convention, with aliases only where the old form uses a different
+     * name (for example tzone -> STIMEZONE and paypal-email -> PAYPAL_EMAIL).
+     */
+    private function buildReplacements(): array
+    {
+        $templatePath = $this->root . '/install/data/constant_format.tpl';
+        $text = file_get_contents($templatePath);
+        if ($text === false) {
+            $this->fail('Cannot read installer configuration template.');
+        }
+
+        preg_match_all('/%([A-Z0-9_]+)%/', $text, $matches);
+        $placeholders = array_unique($matches[0] ?? []);
+
+        $aliases = [
+            '%STIMEZONE%' => 'tzone',
+            '%SERVERNAME%' => 'servername',
+            '%SSTARTDATE%' => 'start_date',
+            '%SSTARTTIME%' => 'start_time',
+            '%PAYPAL_EMAIL%' => 'paypal-email',
+            '%PAYPAL_CURRENCY%' => 'paypal-currency',
+            '%PLUS_PACKAGE_A_GOLD%' => 'plus-a-gold',
+            '%PLUS_PACKAGE_A_PRICE%' => 'plus-a-price',
+            '%PLUS_PACKAGE_B_GOLD%' => 'plus-b-gold',
+            '%PLUS_PACKAGE_B_PRICE%' => 'plus-b-price',
+            '%PLUS_PACKAGE_C_GOLD%' => 'plus-c-gold',
+            '%PLUS_PACKAGE_C_PRICE%' => 'plus-c-price',
+            '%PLUS_PACKAGE_D_GOLD%' => 'plus-d-gold',
+            '%PLUS_PACKAGE_D_PRICE%' => 'plus-d-price',
+            '%PLUS_PACKAGE_E_GOLD%' => 'plus-e-gold',
+            '%PLUS_PACKAGE_E_PRICE%' => 'plus-e-price',
+            '%GP_LOCATE%' => 'gp_locate',
+            '%CRONKEY%' => null,
+            '%STARTTIME%' => null,
+            '%ERROR%' => 'error',
+        ];
+
+        $defaults = [
+            '%SERVERNAME%' => 'TravianZ',
+            '%SPEED%' => '1',
+            '%INCSPEED%' => '1',
+            '%EVASIONSPEED%' => '1',
+            '%TRADERCAP%' => '1',
+            '%CRANNYCAP%' => '1',
+            '%TRAPPERCAP%' => '1',
+            '%STORAGE_MULTIPLIER%' => '1',
+            '%MAX%' => '100',
+            '%LANG%' => 'en',
+            '%STIMEZONE%' => 'Europe/Bucharest',
+            '%BEGINNER%' => '43200',
+            '%REG_OPEN%' => 'true',
+            '%TS_THRESHOLD%' => '20',
+            '%MEDALINTERVAL%' => '0',
+            '%GREAT_WKS%' => 'false',
+            '%WW%' => 'false',
+            '%SHOW_NATARS%' => 'false',
+            '%NATARS_UNITS%' => '100',
+            '%NATARS_SPAWN_TIME%' => '260',
+            '%NATARS_WW_SPAWN_TIME%' => '260',
+            '%NATARS_WW_BUILDING_PLAN_SPAWN_TIME%' => '260',
+            '%NATARS_WW_START_DELAY%' => '10',
+            '%NATURE_REGTIME%' => '43200',
+            '%OASIS_WOOD_MULTIPLIER%' => '40',
+            '%OASIS_CLAY_MULTIPLIER%' => '40',
+            '%OASIS_IRON_MULTIPLIER%' => '40',
+            '%OASIS_CROP_MULTIPLIER%' => '40',
+            '%CRONLOOP%' => '300',
+            '%CRONTICK%' => '60',
+            '%CLEANUPREPORTS%' => '14',
+            '%CLEANUPCHAT%' => '7',
+            '%CLEANUPMESSAGES%' => '0',
+            '%HEROBASEREGEN%' => '10',
+            '%HEROSILVERPERGOLD%' => '10',
+            '%HEROSILVERTOGOLD%' => '25',
+            '%HERORESALL%' => '3',
+            '%HERORESONE%' => '10',
+            '%ERRORREPORT%' => '0',
+            '%GP%' => 'false',
+            '%GP_LOCATE%' => 'gpack/travian_default/',
+            '%ALLIANCEBONUSES%' => 'false',
+            '%PLUSSTATS%' => 'true',
+            '%PLUSSTATSHOURS%' => '6',
+            '%PLUSSTATSKEEP%' => '0',
+            '%USRNMSPECIAL%' => 'true',
+            '%USRNMMIN%' => '3',
+            '%USRNMMAX%' => '15',
+            '%PWMIN%' => '4',
+            '%WWIMAGE%' => 'true',
+            '%PROTECTEDPLAYERS%' => '',
+            '%ASUPPMSGS%' => 'true',
+            '%ARAIDS%' => 'false',
+            '%ARANK%' => 'false',
+            '%CONNECTT%' => '1',
+            '%DOMAIN%' => '',
+            '%HOMEPAGE%' => '',
+            '%SERVER%' => '',
+            '%LIMIT_MAILBOX%' => '0',
+            '%MAX_MAILS%' => '100',
+            '%DEMOLISH%' => 'true',
+            '%BOX1%' => 'false',
+            '%BOX2%' => 'false',
+            '%BOX3%' => 'false',
+            '%VILLAGE_EXPAND%' => '0',
+            '%PLUS_TIME%' => '0',
+            '%PLUS_PRODUCTION%' => '0',
+            '%PAYPAL_EMAIL%' => '',
+            '%PAYPAL_CURRENCY%' => 'EUR',
+            '%PEACE%' => '0',
+            '%T4_COMING%' => 'false',
+        ];
+
+        $replacements = [];
+        foreach ($placeholders as $placeholder) {
+            if (array_key_exists($placeholder, $aliases) && $aliases[$placeholder] !== null) {
+                $field = $aliases[$placeholder];
+            } else {
+                $field = strtolower(trim($placeholder, '%'));
+            }
+
+            if (isset($_POST[$field]) && !is_array($_POST[$field])) {
+                $value = (string) $_POST[$field];
+            } elseif (array_key_exists($placeholder, $defaults)) {
+                $value = (string) $defaults[$placeholder];
+            } else {
+                // Preserve the old installer's behavior for optional fields:
+                // an absent option becomes an empty string rather than leaving
+                // an unresolved %PLACEHOLDER% in the generated PHP file.
+                $value = '';
+            }
+
+            if ($placeholder === '%STIMEZONE%') {
+                $tz = explode(',', $value, 2);
+                $value = $tz[1] ?? $value;
+            }
+
+            $replacements[$placeholder] = $value;
+        }
+
+        $replacements['%STARTTIME%'] = time();
+        $replacements['%CRONKEY%'] = bin2hex(random_bytes(24));
+
+        // The registry owns these values; a form cannot redirect an instance
+        // to another database or table prefix.
+        $registry = $this->readRegistry();
+        if (isset($registry[(string) $_POST['instance_id']])) {
+            $instance = $registry[(string) $_POST['instance_id']];
+            $replacements['%SERVERNAME%'] = (string) ($instance['name'] ?? $replacements['%SERVERNAME%']);
+            $replacements['%SDB%'] = (string) ($instance['database'] ?? '');
+            $replacements['%PREFIX%'] = (string) ($instance['prefix'] ?? '');
+            $replacements['%SSERVER%'] = (string) ($_POST['sserver'] ?? 'localhost');
+            $replacements['%SPORT%'] = (string) ($_POST['sport'] ?? '3306');
+            $replacements['%SUSER%'] = (string) ($_POST['suser'] ?? '');
+            $replacements['%SPASS%'] = (string) ($_POST['spass'] ?? '');
+        }
+
+        return $replacements;
+    }
+
+    private function writeConfig(string $instanceId): void
+    {
+        $replacements = $this->buildReplacements();
+        $path = TravianZInstanceConfigWriter::write($instanceId, $replacements);
+
+        $this->updateStatus($instanceId, 'configured', [
+            'config' => $path,
+            'configured_at' => date('c'),
+        ]);
+
+        $this->redirect('multi.php?instance=' . rawurlencode($instanceId));
+    }
+
+    private function loadInstanceBootstrap(): void
+    {
+        require_once $this->root . '/GameEngine/Instance/Bootstrap.php';
+    }
+
+    private function createStructure(string $instanceId): void
+    {
+        global $database;
+
+        require_once $this->root . '/GameEngine/Database.php';
+        require_once $this->root . '/GameEngine/Admin/database.php';
+
+        $result = $database->createDbStructure();
+        if ($result === false) {
+            $this->fail('Database structure creation failed.');
+        }
+        if ($result === -1) {
+            $this->fail('Database structure already exists or installation requires attention.');
+        }
+
+        $this->updateStatus($instanceId, 'structure_created', ['structure_at' => date('c')]);
+        $this->redirect('multi.php?instance=' . rawurlencode($instanceId));
+    }
+
+    private function createWorld(string $instanceId): void
+    {
+        global $database;
+
+        require_once $this->root . '/GameEngine/Database.php';
+        require_once $this->root . '/GameEngine/Admin/database.php';
+
+        $result = $database->populateWorldData();
+        if ($result === false) {
+            $this->fail('World data creation failed.');
+        }
+        if ($result === -1) {
+            $this->fail('World data already exists or installation requires attention.');
+        }
+
+        $this->updateStatus($instanceId, 'world_created', ['world_at' => date('c')]);
+        $this->redirect('multi.php?instance=' . rawurlencode($instanceId));
+    }
+
+    private function finalize(string $instanceId): void
+    {
+        $registry = $this->readRegistry();
+        if (!isset($registry[$instanceId])) {
+            $this->fail('Instance not found.');
+        }
+
+        $instancePath = $this->root . '/instances/' . $instanceId;
+        if (!is_dir($instancePath) && !mkdir($instancePath, 0775, true) && !is_dir($instancePath)) {
+            $this->fail('Cannot create instance directory.');
+        }
+
+        $installedMarker = $instancePath . '/installed';
+        if (file_put_contents($installedMarker, date('c') . PHP_EOL, LOCK_EX) === false) {
+            $this->fail('Cannot create instance installed marker.');
+        }
+
+        $this->updateStatus($instanceId, 'installed', ['installed_at' => date('c')]);
+        $this->redirect('multi.php?instance=' . rawurlencode($instanceId));
+    }
+
+    private function readRegistry(): array
+    {
+        if (!is_file($this->instancesFile)) {
+            return [];
+        }
+
+        $data = json_decode((string) file_get_contents($this->instancesFile), true);
+        return is_array($data) ? $data : [];
+    }
+
+    private function updateStatus(string $instanceId, string $status, array $extra = []): void
+    {
+        $registry = $this->readRegistry();
+        if (!isset($registry[$instanceId]) || !is_array($registry[$instanceId])) {
+            return;
+        }
+
+        $registry[$instanceId]['status'] = $status;
+        $registry[$instanceId]['updated_at'] = date('c');
+        foreach ($extra as $key => $value) {
+            $registry[$instanceId][$key] = $value;
+        }
+
+        $dir = dirname($this->instancesFile);
+        if (!is_dir($dir)) {
+            @mkdir($dir, 0775, true);
+        }
+
+        $tmp = $this->instancesFile . '.tmp';
+        if (file_put_contents($tmp, json_encode($registry, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES) . PHP_EOL, LOCK_EX) === false) {
+            $this->fail('Cannot update instance registry.');
+        }
+        if (!rename($tmp, $this->instancesFile)) {
+            @unlink($tmp);
+            $this->fail('Cannot activate instance registry update.');
+        }
+    }
+
+    private function redirect(string $location): void
+    {
+        header('Location: ' . $location);
+        exit;
+    }
+
+    private function fail(string $message): void
+    {
+        http_response_code(500);
+        echo '<h1>TravianZ Multi-Instance Installer</h1>';
+        echo '<p>' . htmlspecialchars($message, ENT_QUOTES, 'UTF-8') . '</p>';
+        exit;
+    }
+}
+
+(new TravianZInstanceInstallProcess())->run();