diff --git a/modules/pihole/pages/instances.php b/modules/pihole/pages/instances.php
index f617068..f4599aa 100644
--- a/modules/pihole/pages/instances.php
+++ b/modules/pihole/pages/instances.php
@@ -9,6 +9,143 @@ require_admin();
 $settings = modules()->settings($moduleName);
 $notice = null;
 $error = null;
+$testResults = [];
+
+$httpRequest = static function (string $method, string $url, array $headers, ?string $body, bool $verify, int $timeout): array {
+    $raw = '';
+    $httpCode = 0;
+    $requestError = '';
+
+    if (function_exists('curl_init')) {
+        $ch = curl_init($url);
+        curl_setopt_array($ch, [
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_TIMEOUT => $timeout,
+            CURLOPT_CONNECTTIMEOUT => $timeout,
+            CURLOPT_SSL_VERIFYPEER => $verify,
+            CURLOPT_SSL_VERIFYHOST => $verify ? 2 : 0,
+            CURLOPT_CUSTOMREQUEST => $method,
+            CURLOPT_HTTPHEADER => $headers,
+        ]);
+        if ($body !== null) {
+            curl_setopt($ch, CURLOPT_POSTFIELDS, $body);
+        }
+        $raw = (string)curl_exec($ch);
+        if ($raw === '' && curl_errno($ch)) {
+            $requestError = curl_error($ch);
+        }
+        $httpCode = (int)curl_getinfo($ch, CURLINFO_HTTP_CODE);
+        curl_close($ch);
+    } else {
+        $ctx = stream_context_create([
+            'http' => [
+                'method' => $method,
+                'timeout' => $timeout,
+                'header' => implode("\r\n", $headers),
+                'content' => $body ?? '',
+            ],
+            'ssl' => [
+                'verify_peer' => $verify,
+                'verify_peer_name' => $verify,
+            ],
+        ]);
+        $raw = (string)@file_get_contents($url, false, $ctx);
+        if ($raw === '') {
+            $requestError = 'HTTP request failed';
+        } else {
+            $httpCode = 200;
+        }
+    }
+
+    if ($requestError !== '') {
+        return ['ok' => false, 'http_code' => $httpCode, 'error' => $requestError, 'raw' => $raw, 'url' => $url];
+    }
+
+    $decoded = json_decode($raw, true);
+    if (!is_array($decoded)) {
+        return ['ok' => false, 'http_code' => $httpCode, 'error' => 'invalid_json', 'raw' => $raw, 'url' => $url];
+    }
+
+    return ['ok' => true, 'http_code' => $httpCode, 'data' => $decoded, 'url' => $url];
+};
+
+$runConnectionTest = static function (array $instance, array $settings) use ($httpRequest): array {
+    $verifyTls = !isset($settings['verify_tls']) || $settings['verify_tls'] === '1' || $settings['verify_tls'] === 1 || $settings['verify_tls'] === true;
+    $timeout = (int)($settings['api_timeout_sec'] ?? 8);
+    if ($timeout <= 0) {
+        $timeout = 8;
+    }
+
+    $url = rtrim((string)($instance['url'] ?? ''), '/');
+    $password = trim((string)($instance['password'] ?? ''));
+    $v6AuthUrl = $url . '/api/auth';
+    $v6Payload = json_encode(['password' => $password], JSON_UNESCAPED_UNICODE);
+    $v6Auth = $httpRequest('POST', $v6AuthUrl, ['Accept: application/json', 'Content-Type: application/json'], $v6Payload, $verifyTls, $timeout);
+
+    if ($v6Auth['ok']) {
+        $session = (array)(($v6Auth['data']['session'] ?? []) ?: []);
+        $sid = trim((string)($session['sid'] ?? ''));
+        if ($sid !== '') {
+            $probe = $httpRequest('GET', $url . '/api/stats/summary', ['Accept: application/json', 'X-FTL-SID: ' . $sid], null, $verifyTls, $timeout);
+            if ($probe['ok']) {
+                return [
+                    'ok' => true,
+                    'status' => 'ok',
+                    'message' => 'Verbindung OK. API v6 antwortet.',
+                    'version' => 6,
+                    'details' => ['auth' => $v6Auth, 'probe' => $probe],
+                ];
+            }
+
+            return [
+                'ok' => false,
+                'status' => 'error',
+                'message' => 'v6 Auth OK, aber Stats-Endpoint antwortet nicht sauber.',
+                'version' => 6,
+                'details' => ['auth' => $v6Auth, 'probe' => $probe],
+            ];
+        }
+    }
+
+    $legacyUrl = $url . '/admin/api.php?summaryRaw';
+    if ($password !== '') {
+        $legacyUrl .= '&auth=' . rawurlencode($password);
+    }
+    $v5Probe = $httpRequest('GET', $legacyUrl, ['Accept: application/json'], null, $verifyTls, $timeout);
+    if ($v5Probe['ok']) {
+        return [
+            'ok' => true,
+            'status' => 'ok',
+            'message' => 'Verbindung OK. API v5 antwortet.',
+            'version' => 5,
+            'details' => ['auth' => $v6Auth, 'probe' => $v5Probe],
+        ];
+    }
+
+    $status = 'error';
+    $message = 'Unbekannter Fehler.';
+    $httpCode = (int)($v6Auth['http_code'] ?? $v5Probe['http_code'] ?? 0);
+    $requestError = (string)($v6Auth['error'] ?? $v5Probe['error'] ?? 'error');
+    if ($httpCode === 0) {
+        $status = 'unreachable';
+        $message = 'Host nicht erreichbar oder kein HTTP-Response.';
+    } elseif ($httpCode === 401 || $httpCode === 403) {
+        $status = 'auth';
+        $message = 'Passwort oder App-Passwort falsch oder nicht berechtigt.';
+    } elseif ($requestError === 'invalid_json') {
+        $status = 'invalid';
+        $message = 'API antwortet nicht mit JSON. URL pruefen.';
+    } else {
+        $message = 'API Fehler: ' . $requestError . ' (HTTP ' . $httpCode . ')';
+    }
+
+    return [
+        'ok' => false,
+        'status' => $status,
+        'message' => $message,
+        'details' => ['auth' => $v6Auth, 'probe' => $v5Probe],
+    ];
+};
 
 $loadInstances = function (array $settings): array {
     $normalizeSecret = static function (array $row): string {
@@ -79,6 +216,7 @@ $saveInstances = function (array $settings, array $instances): void {
 
 if ($_SERVER['REQUEST_METHOD'] === 'POST') {
     $deleteId = trim((string)($_POST['delete_id'] ?? ''));
+    $testId = trim((string)($_POST['test_id'] ?? ''));
     $currentId = trim((string)($_POST['current_id'] ?? ''));
     $instanceId = trim((string)($_POST['instance_id'] ?? ''));
     $name = trim((string)($_POST['name'] ?? ''));
@@ -86,7 +224,30 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
     $password = trim((string)($_POST['password'] ?? ''));
     $isPrimary = isset($_POST['is_primary']);
 
-    if ($deleteId !== '') {
+    if ($testId !== '') {
+        if (isset($instances[$testId])) {
+            module_debug_push('pihole', [
+                'label' => 'connection.test.start',
+                'instance_id' => $testId,
+                'instance_name' => (string)($instances[$testId]['name'] ?? $testId),
+                'url' => (string)($instances[$testId]['url'] ?? ''),
+            ]);
+
+            $result = $runConnectionTest($instances[$testId], $settings);
+            $testResults[$testId] = $result;
+
+            module_debug_push('pihole', [
+                'label' => 'connection.test.result',
+                'instance_id' => $testId,
+                'instance_name' => (string)($instances[$testId]['name'] ?? $testId),
+                'result' => $result,
+            ]);
+
+            $notice = $result['message'] ?? null;
+        } else {
+            $error = 'Test-Instanz nicht gefunden.';
+        }
+    } elseif ($deleteId !== '') {
         if (isset($instances[$deleteId])) {
             unset($instances[$deleteId]);
             $notice = 'Instanz geloescht.';
@@ -189,13 +350,16 @@ if ($primaryId === '') {
             </div>
             <div class="pihole-card-actions">
               <button class="module-button module-button--secondary module-button--small" type="button" data-instance-edit>Bearbeiten</button>
-              <button class="module-button module-button--secondary module-button--small" type="button" data-instance-test>Test Verbindung</button>
+              <form method="post">
+                <input type="hidden" name="test_id" value="<?= e((string)($instance['id'] ?? '')) ?>">
+                <button class="module-button module-button--secondary module-button--small" type="submit" data-instance-test>Test Verbindung</button>
+              </form>
               <form method="post" onsubmit="return confirm('Instanz wirklich loeschen?')">
                 <input type="hidden" name="delete_id" value="<?= e((string)($instance['id'] ?? '')) ?>">
                 <button class="module-button module-button--secondary module-button--small" type="submit">Loeschen</button>
               </form>
             </div>
-            <div class="pihole-test-result" data-instance-result></div>
+            <div class="pihole-test-result<?= !empty($testResults[$instance['id']]['status']) ? ' is-' . e((string)$testResults[$instance['id']]['status']) : '' ?>" data-instance-result><?= e((string)($testResults[$instance['id']]['message'] ?? '')) ?></div>
           </div>
         <?php endforeach; ?>
       <?php endif; ?>