diff --git a/rosbridge_library/src/rosbridge_library/capabilities/advertise_action.py b/rosbridge_library/src/rosbridge_library/capabilities/advertise_action.py
index 9cff54d8a..4341e8a43 100644
--- a/rosbridge_library/src/rosbridge_library/capabilities/advertise_action.py
+++ b/rosbridge_library/src/rosbridge_library/capabilities/advertise_action.py
@@ -51,9 +51,9 @@ class AdvertisedActionHandler:
     def __init__(
         self, action_name: str, action_type: str, protocol: Protocol, sleep_time: float = 0.001
     ) -> None:
-        self.goal_futures = {}
-        self.goal_handles = {}
-        self.goal_statuses = {}
+        self.goal_futures: dict[str, rclpy.task.Future] = {}
+        self.goal_handles: dict[str, Any] = {}
+        self.goal_statuses: dict[str, GoalStatus] = {}
 
         self.action_name = action_name
         self.action_type = action_type
diff --git a/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py b/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py
index 1757a1179..7809622a7 100644
--- a/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py
+++ b/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py
@@ -30,7 +30,7 @@ def spam(self):
     #     }
     # },
     # ...
-    lists = {}
+    lists: dict[str, dict] = {}
 
     def __init__(self):
         """Create singleton instance"""
diff --git a/rosbridge_library/src/rosbridge_library/capabilities/send_action_goal.py b/rosbridge_library/src/rosbridge_library/capabilities/send_action_goal.py
index 089d84562..db74333db 100644
--- a/rosbridge_library/src/rosbridge_library/capabilities/send_action_goal.py
+++ b/rosbridge_library/src/rosbridge_library/capabilities/send_action_goal.py
@@ -33,6 +33,7 @@
 import fnmatch
 from functools import partial
 from threading import Thread
+from typing import Any
 
 from action_msgs.msg import GoalStatus
 from rosbridge_library.capability import Capability
@@ -52,7 +53,7 @@ class SendActionGoal(Capability):
     cancel_action_goal_msg_fields = [(True, "action", str)]
 
     actions_glob = None
-    client_handler_list = {}
+    client_handler_list: dict[str, ActionClientHandler] = {}
 
     def __init__(self, protocol: Protocol) -> None:
         # Call superclass constructor
@@ -182,7 +183,7 @@ def _failure(self, cid: str, action: str, exc: Exception) -> None:
             outgoing_message["id"] = cid
         self.protocol.send(outgoing_message)
 
-    def _feedback(self, cid: str, action: str, message: dict) -> None:
+    def _feedback(self, cid: str, action: str, message: Any) -> None:
         outgoing_message = {
             "op": "action_feedback",
             "action": action,
diff --git a/rosbridge_library/src/rosbridge_library/capabilities/subscribe.py b/rosbridge_library/src/rosbridge_library/capabilities/subscribe.py
index c54e80094..0f523ab22 100644
--- a/rosbridge_library/src/rosbridge_library/capabilities/subscribe.py
+++ b/rosbridge_library/src/rosbridge_library/capabilities/subscribe.py
@@ -40,10 +40,10 @@
 from rosbridge_library.internal.subscription_modifiers import MessageHandler
 
 try:
-    from ujson import dumps as encode_json
+    from ujson import dumps as encode_json  # type: ignore[import-untyped]
 except ImportError:
     try:
-        from simplejson import dumps as encode_json
+        from simplejson import dumps as encode_json  # type: ignore[import-untyped]
     except ImportError:
         from json import dumps as encode_json
 
diff --git a/rosbridge_library/src/rosbridge_library/internal/actions.py b/rosbridge_library/src/rosbridge_library/internal/actions.py
index efc9211cc..8e3a0273e 100644
--- a/rosbridge_library/src/rosbridge_library/internal/actions.py
+++ b/rosbridge_library/src/rosbridge_library/internal/actions.py
@@ -32,7 +32,7 @@
 
 import time
 from threading import Thread
-from typing import Any, Callable, Optional, Union
+from typing import Any, Callable, Optional
 
 from rclpy.action import ActionClient
 from rclpy.expand_topic_name import expand_topic_name
@@ -59,9 +59,9 @@ def __init__(
         action: str,
         action_type: str,
         args: dict,
-        success_callback: Callable[[str, str, int, bool, dict], None],
-        error_callback: Callable[[str, str, Exception], None],
-        feedback_callback: Callable[[str, str, dict], None],
+        success_callback: Callable[[dict], None],
+        error_callback: Callable[[Exception], None],
+        feedback_callback: Optional[Callable[[dict], None]],
         node_handle: Node,
     ) -> None:
         """
@@ -90,12 +90,11 @@ def __init__(
         self.error = error_callback
         self.feedback = feedback_callback
         self.node_handle = node_handle
-        self.send_goal_helper = None
+        self.send_goal_helper = SendGoal()
 
     def run(self) -> None:
         try:
             # Call the service and pass the result to the success handler
-            self.send_goal_helper = SendGoal()
             self.success(
                 self.send_goal_helper.send_goal(
                     self.node_handle,
@@ -110,7 +109,7 @@ def run(self) -> None:
             self.error(e)
 
 
-def args_to_action_goal_instance(action: str, inst: Any, args: Union[list, dict]) -> Any:
+def args_to_action_goal_instance(action: str, inst: Any, args: list | dict | None) -> Any:
     """ "
     Populate an action goal instance with the provided args
 
@@ -142,6 +141,7 @@ def get_result_cb(self, future: Future) -> None:
 
     def goal_response_cb(self, future: Future) -> None:
         self.goal_handle = future.result()
+        assert self.goal_handle is not None
         if not self.goal_handle.accepted:
             raise Exception("Action goal was rejected")
         result_future = self.goal_handle.get_result_async()
@@ -156,7 +156,7 @@ def send_goal(
         action: str,
         action_type: str,
         args: Optional[dict] = None,
-        feedback_cb: Optional[Callable[[str, str, dict], None]] = None,
+        feedback_cb: Optional[Callable[[dict], None]] = None,
     ) -> dict:
         # Given the action name and type, fetch a request instance
         action_name = expand_topic_name(action, node_handle.get_name(), node_handle.get_namespace())
diff --git a/rosbridge_library/src/rosbridge_library/internal/ros_loader.py b/rosbridge_library/src/rosbridge_library/internal/ros_loader.py
index c45abb896..d3efa1664 100644
--- a/rosbridge_library/src/rosbridge_library/internal/ros_loader.py
+++ b/rosbridge_library/src/rosbridge_library/internal/ros_loader.py
@@ -43,9 +43,9 @@
 """
 
 # Variable containing the loaded classes
-_loaded_msgs = {}
-_loaded_srvs = {}
-_loaded_actions = {}
+_loaded_msgs: dict[str, Any] = {}
+_loaded_srvs: dict[str, Any] = {}
+_loaded_actions: dict[str, Any] = {}
 _msgs_lock = Lock()
 _srvs_lock = Lock()
 _actions_lock = Lock()
@@ -185,7 +185,7 @@ def _get_class(typestring: str, subname: str, cache: Dict[str, Any], lock: Lock)
     return cls
 
 
-def _load_class(modname: str, subname: str, classname: str) -> None:
+def _load_class(modname: str, subname: str, classname: str) -> Any:
     """Loads the manifest and imports the module that contains the specified
     type.
 
@@ -220,7 +220,7 @@ def _splittype(typestring: str) -> Tuple[str, str]:
     raise InvalidTypeStringException(typestring)
 
 
-def _add_to_cache(cache: Dict[str, Any], lock: Lock, key: str, value: any) -> None:
+def _add_to_cache(cache: Dict[str, Any], lock: Lock, key: str, value: Any) -> None:
     lock.acquire()
     cache[key] = value
     lock.release()
diff --git a/rosbridge_library/src/rosbridge_library/internal/services.py b/rosbridge_library/src/rosbridge_library/internal/services.py
index 59a76da7d..547877ef8 100644
--- a/rosbridge_library/src/rosbridge_library/internal/services.py
+++ b/rosbridge_library/src/rosbridge_library/internal/services.py
@@ -58,8 +58,8 @@ def __init__(
         self,
         service: str,
         args: dict,
-        success_callback: Callable[[str, str, int, bool, Any], None],
-        error_callback: Callable[[str, str, Exception], None],
+        success_callback: Callable[[dict], None],
+        error_callback: Callable[[Exception], None],
         node_handle: Node,
     ) -> None:
         """Create a service caller for the specified service.  Use start()
@@ -94,7 +94,7 @@ def run(self) -> None:
             self.error(e)
 
 
-def args_to_service_request_instance(service: str, inst: Any, args: dict) -> Any:
+def args_to_service_request_instance(service: str, inst: Any, args: list | dict | None) -> Any:
     """Populate a service request instance with the provided args
 
     args can be a dictionary of values, or a list, or None
@@ -122,14 +122,14 @@ def call_service(
     service = expand_topic_name(service, node_handle.get_name(), node_handle.get_namespace())
 
     service_names_and_types = dict(node_handle.get_service_names_and_types())
-    service_type = service_names_and_types.get(service)
-    if service_type is None:
+    service_types = service_names_and_types.get(service)
+    if service_types is None:
         raise InvalidServiceException(service)
 
     # service_type is a tuple of types at this point; only one type is supported.
-    if len(service_type) > 1:
-        node_handle.get_logger().warning(f"More than one service type detected: {service_type}")
-    service_type = service_type[0]
+    if len(service_types) > 1:
+        node_handle.get_logger().warning(f"More than one service type detected: {service_types}")
+    service_type = service_types[0]
 
     service_class = get_service_class(service_type)
     inst = get_service_request_instance(service_type)
diff --git a/rosbridge_library/src/rosbridge_library/protocol.py b/rosbridge_library/src/rosbridge_library/protocol.py
index 9d91076c9..9d6e54f61 100644
--- a/rosbridge_library/src/rosbridge_library/protocol.py
+++ b/rosbridge_library/src/rosbridge_library/protocol.py
@@ -31,6 +31,7 @@
 # POSSIBILITY OF SUCH DAMAGE.
 
 import time
+from typing import Any
 
 from rosbridge_library.capabilities.fragmentation import Fragmentation
 from rosbridge_library.util import bson, json
@@ -81,9 +82,9 @@ class Protocol:
     # !! this might be related to (or even be avoided by using) throttle_rate !!
     delay_between_messages = 0
     # global list of non-ros advertised services
-    external_service_list = {}
+    external_service_list: dict[str, Any] = {}
     # global list of non-ros advertised actions
-    external_action_list = {}
+    external_action_list: dict[str, Any] = {}
     # Use only BSON for the whole communication if the server has been started with bson_only_mode:=True
     bson_only_mode = False
 
diff --git a/rosbridge_library/src/rosbridge_library/util/__init__.py b/rosbridge_library/src/rosbridge_library/util/__init__.py
index 8b04567e1..359021ae0 100644
--- a/rosbridge_library/src/rosbridge_library/util/__init__.py
+++ b/rosbridge_library/src/rosbridge_library/util/__init__.py
@@ -1,9 +1,9 @@
 # try to import json-lib: 1st try ujson, 2nd try simplejson, else import standard Python json
 try:
-    import ujson as json
+    import ujson as json  # type: ignore[import-untyped]
 except ImportError:
     try:
-        import simplejson as json
+        import simplejson as json  # type: ignore[import-untyped]
     except ImportError:
         import json  # noqa: F401
 
diff --git a/rosbridge_library/test/experimental/complex_srv+tcp/test_non-ros_service_client_complex-srv.py b/rosbridge_library/test/experimental/complex_srv+tcp/test_non-ros_service_client_complex-srv.py
index eefc39f27..24f39f3cb 100755
--- a/rosbridge_library/test/experimental/complex_srv+tcp/test_non-ros_service_client_complex-srv.py
+++ b/rosbridge_library/test/experimental/complex_srv+tcp/test_non-ros_service_client_complex-srv.py
@@ -67,13 +67,13 @@ def request_service():
         try:
             incoming = sock.recv(max_msg_length)  # receive service_response from rosbridge
             if buffer == "":
-                buffer = incoming
+                buffer = incoming.decode("utf-8")
                 if incoming == "":
                     print("closing socket")
                     sock.close()
                     break
             else:
-                buffer = buffer + incoming
+                buffer = buffer + incoming.decode("utf-8")
             # print "buffer-length:", len(buffer)
             try:  # try to access service_request directly (not fragmented)
                 data_object = json.loads(buffer)
@@ -90,14 +90,14 @@ def request_service():
                     "}{"
                 )  # split buffer into fragments and re-fill curly brackets
                 result = []
-                for fragment in result_string:
-                    if fragment[0] != "{":
-                        fragment = "{" + fragment
-                    if fragment[len(fragment) - 1] != "}":
-                        fragment = fragment + "}"
+                for fragment_str in result_string:
+                    if fragment_str[0] != "{":
+                        fragment_str = "{" + fragment_str
+                    if fragment_str[len(fragment_str) - 1] != "}":
+                        fragment_str = fragment_str + "}"
                     try:
                         result.append(
-                            json.loads(fragment)
+                            json.loads(fragment_str)
                         )  # try to parse json from string, and append if successful
                     except Exception:
                         # print(e)
diff --git a/rosbridge_library/test/experimental/fragmentation+srv+tcp/test_non-ros_service_client_fragmented.py b/rosbridge_library/test/experimental/fragmentation+srv+tcp/test_non-ros_service_client_fragmented.py
index 368d6c04c..e80ec9621 100755
--- a/rosbridge_library/test/experimental/fragmentation+srv+tcp/test_non-ros_service_client_fragmented.py
+++ b/rosbridge_library/test/experimental/fragmentation+srv+tcp/test_non-ros_service_client_fragmented.py
@@ -1,5 +1,6 @@
 #!/usr/bin/python
 import socket
+from typing import Any
 
 from rosbridge_library.util import json
 
@@ -63,13 +64,13 @@ def request_service():
         try:
             incoming = sock.recv(max_msg_length)  # receive service_response from rosbridge
             if buffer == "":
-                buffer = incoming
+                buffer = incoming.decode("utf-8")
                 if incoming == "":
                     print("closing socket")
                     sock.close()
                     break
             else:
-                buffer = buffer + incoming
+                buffer = buffer + incoming.decode("utf-8")
             # print "buffer-length:", len(buffer)
             try:  # try to access service_request directly (not fragmented)
                 data_object = json.loads(buffer)
@@ -86,14 +87,14 @@ def request_service():
                     "}{"
                 )  # split buffer into fragments and re-fill curly brackets
                 result = []
-                for fragment in result_string:
-                    if fragment[0] != "{":
-                        fragment = "{" + fragment
-                    if fragment[len(fragment) - 1] != "}":
-                        fragment = fragment + "}"
+                for fragment_str in result_string:
+                    if fragment_str[0] != "{":
+                        fragment_str = "{" + fragment_str
+                    if fragment_str[len(fragment_str) - 1] != "}":
+                        fragment_str = fragment_str + "}"
                     try:
                         result.append(
-                            json.loads(fragment)
+                            json.loads(fragment_str)
                         )  # try to parse json from string, and append if successful
                     except Exception:
                         # print(e)
@@ -105,7 +106,7 @@ def request_service():
                 announced = int(result[0]["total"])
                 if fragment_count == announced:  # if all fragments received --> sort and defragment
                     # sort fragments
-                    sorted_result = [None] * fragment_count
+                    sorted_result: list[Any] = [None] * fragment_count
                     unsorted_result = []
                     for fragment in result:
                         unsorted_result.append(fragment)