diff --git a/src/metrics_utils.rs b/src/metrics_utils.rs
index 0fcb043..a58af43 100644
--- a/src/metrics_utils.rs
+++ b/src/metrics_utils.rs
@@ -5,13 +5,17 @@ use std::{
 
 use metrics::{describe_counter, describe_gauge, describe_histogram, gauge, histogram};
 
+// counters
 pub const OPENED_TOTAL: &str = "mobc_pool_connections_opened_total";
 pub const CLOSED_TOTAL: &str = "mobc_pool_connections_closed_total";
-pub const OPEN_CONNECTIONS: &str = "mobc_pool_connections_open";
 
+// gauges
+pub const OPEN_CONNECTIONS: &str = "mobc_pool_connections_open";
 pub const ACTIVE_CONNECTIONS: &str = "mobc_pool_connections_busy";
 pub const IDLE_CONNECTIONS: &str = "mobc_pool_connections_idle";
 pub const WAIT_COUNT: &str = "mobc_client_queries_wait";
+
+// histogram
 pub const WAIT_DURATION: &str = "mobc_client_queries_wait_histogram_ms";
 
 pub fn describe_metrics() {