diff --git a/bin/crawl.php b/bin/crawl.php
index c42578a..f86c263 100755
--- a/bin/crawl.php
+++ b/bin/crawl.php
@@ -25,6 +25,7 @@
         $urls = extract_urls_recursively($url, $depth, 'extract_unique_urls');
         break;
     case 'worker':
+        predis()->del('visited');
         $urls = extract_urls_with_worker($url, $depth, uniqid());
         break;
     case 'promise':
diff --git a/bin/worker.php b/bin/worker.php
index f12783e..48279a7 100755
--- a/bin/worker.php
+++ b/bin/worker.php
@@ -23,7 +23,7 @@ function blpop(string $key): string {
     // upravit kód tak, aby nedocházelo ke ztrátě dat
     // if (rand(0,1)) exit(1);
 
-    foreach (extract_urls($url) as $u) {
+    foreach (worker_extract_unique_urls($url) as $u) {
         predis()->rpush($results, json_encode($u));
 
         if ($depth > 0) {
diff --git a/src/functions.php b/src/functions.php
index e14f379..5838d07 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -51,6 +51,15 @@ function predis(): Predis\Client {
     return $client ?? $client = new Predis\Client('tcp://redis');
 }
 
+// extrahuje pouze unikátní URL ze zadané adresy
+function worker_extract_unique_urls(string $url): Generator {
+    foreach (extract_urls($url) as $u) {
+        if (predis()->hsetnx('visited', md5($u), 1)) {
+            yield $u;
+        }
+    }
+}
+
 // přidá zadanou adresu do fronty pro zpracování workerem
 function extract_urls_with_worker(string $url, int $depth, string $results): Generator {
     predis()->rpush('queue', json_encode([$url, $depth, $results]));