diff --git a/prometheuspvesd/config.py b/prometheuspvesd/config.py
index d6b5084..3556393 100644
--- a/prometheuspvesd/config.py
+++ b/prometheuspvesd/config.py
@@ -3,6 +3,7 @@
 
 import os
 from pathlib import Path, PurePath
+from typing import ClassVar
 
 import anyconfig
 import environs
@@ -20,7 +21,7 @@ cache_dir = AppDirs("prometheus-pve-sd").user_cache_dir
 default_output_file = os.path.join(cache_dir, "pve.json")
 
 
-class Config():
+class Config:
     """
     Create an object with all necessary settings.
 
@@ -30,7 +31,7 @@ class Config():
     - provides cli parameters
     """
 
-    SETTINGS = {
+    SETTINGS: ClassVar[dict[dict]] = {
         "metrics.enabled": {
             "default": True,
             "env": "METRICS_ENABLED",
diff --git a/prometheuspvesd/discovery.py b/prometheuspvesd/discovery.py
index b835b48..bf1f192 100644
--- a/prometheuspvesd/discovery.py
+++ b/prometheuspvesd/discovery.py
@@ -20,7 +20,7 @@ PROPAGATION_TIME = Summary(
 HOST_GAUGE = Gauge("pve_sd_hosts", "Number of hosts discovered by PVE SD")
 
 
-class Discovery():
+class Discovery:
     """Prometheus PVE Service Discovery."""
 
     def __init__(self):
diff --git a/prometheuspvesd/utils.py b/prometheuspvesd/utils.py
index 79fa804..a444a83 100644
--- a/prometheuspvesd/utils.py
+++ b/prometheuspvesd/utils.py
@@ -2,6 +2,7 @@
 """Global utility methods and classes."""
 
 from distutils.util import strtobool
+from typing import ClassVar
 
 
 def to_bool(string):
@@ -11,7 +12,7 @@ def to_bool(string):
 class Singleton(type):
     """Meta singleton class."""
 
-    _instances = {}
+    _instances: ClassVar[dict] = {}
 
     def __call__(cls, *args, **kwargs):
         if cls not in cls._instances: