diff --git a/src/config/basic_client.rs b/src/config/basic_client.rs
index b3dcf29..1ca5758 100644
--- a/src/config/basic_client.rs
+++ b/src/config/basic_client.rs
@@ -5,7 +5,13 @@ use reqwest::Client;
 use crate::config::KeyCheckerConfig;
 
 pub fn client_builder(config: &KeyCheckerConfig) -> Result<Client, reqwest::Error> {
-    let mut builder = Client::builder().timeout(Duration::from_secs(config.timeout_sec));
+    // Adjust connection pool size based on concurrency, optimizing for 0.5 second response time
+    let pool_size = (config.concurrency / 2).max(20).min(config.concurrency);
+
+    let mut builder = Client::builder()
+        .timeout(Duration::from_secs(config.timeout_sec))
+        .pool_max_idle_per_host(pool_size)
+        .pool_idle_timeout(Duration::from_secs(30));
 
     if let Some(ref proxy_url) = config.proxy {
         builder = builder.proxy(reqwest::Proxy::all(proxy_url.clone())?);