diff --git a/src/custom_types.py b/src/custom_types.py
new file mode 100644
index 0000000..c44799c
--- /dev/null
+++ b/src/custom_types.py
@@ -0,0 +1,12 @@
+UsersWatchedStatus = dict[str, str | tuple[str] | dict[str, bool | int]]
+UsersWatched = (
+    dict[
+        frozenset[UsersWatchedStatus],
+        dict[
+            str,
+            list[UsersWatchedStatus]
+            | dict[frozenset[UsersWatchedStatus], list[UsersWatchedStatus]],
+        ],
+    ]
+    | list[UsersWatchedStatus]
+)
diff --git a/src/functions.py b/src/functions.py
index 1e76a26..8b1f69b 100644
--- a/src/functions.py
+++ b/src/functions.py
@@ -1,5 +1,6 @@
 import os
-from concurrent.futures import ThreadPoolExecutor
+from concurrent.futures import Future, ThreadPoolExecutor
+from typing import Any, Callable
 from dotenv import load_dotenv
 
 load_dotenv(override=True)
@@ -8,11 +9,11 @@
 mark_file = os.getenv("MARK_FILE", os.getenv("MARKFILE", "mark.log"))
 
 
-def logger(message: str, log_type=0):
+def logger(message: str, log_type: int = 0):
     debug = str_to_bool(os.getenv("DEBUG", "False"))
     debug_level = os.getenv("DEBUG_LEVEL", "info").lower()
 
-    output = str(message)
+    output: str | None = str(message)
     if log_type == 0:
         pass
     elif log_type == 1 and (debug and debug_level in ("info", "debug")):
@@ -42,12 +43,9 @@ def log_marked(
     username: str,
     library: str,
     movie_show: str,
-    episode: str = None,
-    duration=None,
+    episode: str | None = None,
+    duration: float | None = None,
 ):
-    if mark_file is None:
-        return
-
     output = f"{server_type}/{server_name}/{username}/{library}/{movie_show}"
 
     if episode:
@@ -69,7 +67,7 @@ def str_to_bool(value: str) -> bool:
 
 
 # Search for nested element in list
-def contains_nested(element, lst):
+def contains_nested(element: str, lst: list[tuple[str] | None] | tuple[str] | None):
     if lst is None:
         return None
 
@@ -116,33 +114,39 @@ def match_list(
 
 
 def future_thread_executor(
-    args: list, threads: int = None, override_threads: bool = False
-):
-    futures_list = []
-    results = []
-
-    workers = min(int(os.getenv("MAX_THREADS", 32)), os.cpu_count() * 2)
-    if threads:
+    args: list[tuple[Callable[..., Any], ...]],
+    threads: int | None = None,
+    override_threads: bool = False,
+) -> list[Any]:
+    results: list[Any] = []
+
+    # Determine the number of workers, defaulting to 1 if os.cpu_count() returns None
+    max_threads_env: int = int(os.getenv("MAX_THREADS", 32))
+    cpu_threads: int = os.cpu_count() or 1  # Default to 1 if os.cpu_count() is None
+    workers: int = min(max_threads_env, cpu_threads * 2)
+
+    # Adjust workers based on threads parameter and override_threads flag
+    if threads is not None:
         workers = min(threads, workers)
-
     if override_threads:
-        workers = threads
+        workers = threads if threads is not None else workers
 
     # If only one worker, run in main thread to avoid overhead
     if workers == 1:
-        results = []
         for arg in args:
             results.append(arg[0](*arg[1:]))
         return results
 
     with ThreadPoolExecutor(max_workers=workers) as executor:
+        futures_list: list[Future[Any]] = []
+
         for arg in args:
             # * arg unpacks the list into actual arguments
             futures_list.append(executor.submit(*arg))
 
-        for future in futures_list:
+        for out in futures_list:
             try:
-                result = future.result()
+                result = out.result()
                 results.append(result)
             except Exception as e:
                 raise Exception(e)
diff --git a/src/jellyfin_emby.py b/src/jellyfin_emby.py
index d8f4387..f8afa71 100644
--- a/src/jellyfin_emby.py
+++ b/src/jellyfin_emby.py
@@ -2,7 +2,7 @@
 
 import traceback, os
 from math import floor
-from typing import Literal
+from typing import Any, Literal
 from dotenv import load_dotenv
 import requests
 from packaging.version import parse, Version
@@ -15,6 +15,7 @@
     str_to_bool,
 )
 from src.library import generate_library_guids_dict
+from src.custom_types import UsersWatched
 
 load_dotenv(override=True)
 
@@ -101,10 +102,12 @@ def query(
         query: str,
         query_type: Literal["get", "post"],
         identifiers: dict[str, str] | None = None,
-        json: dict | None = None,
-    ) -> dict | list[dict]:
+        json: dict[str, float] | None = None,
+    ) -> dict[str, Any] | list[dict[str, Any]] | None:
         try:
-            results = None
+            results: (
+                dict[str, list[Any] | dict[str, str]] | list[dict[str, Any]] | None
+            ) = None
 
             if query_type == "get":
                 response = self.session.get(
@@ -140,7 +143,7 @@ def query(
                     raise Exception("Query result is not of type list or dict")
 
             # append identifiers to results
-            if identifiers:
+            if identifiers and results:
                 results["Identifiers"] = identifiers
 
             return results
@@ -158,13 +161,13 @@ def info(
         try:
             query_string = "/System/Info/Public"
 
-            response: dict = self.query(query_string, "get")
+            response: dict[str, Any] = self.query(query_string, "get")
 
             if response:
                 if name_only:
-                    return response.get("ServerName")
+                    return response["ServerName"]
                 elif version_only:
-                    return parse(response.get("Version"))
+                    return parse(response["Version"])
 
                 return f"{self.server_type} {response.get('ServerName')}: {response.get('Version')}"
             else:
@@ -176,15 +179,16 @@ def info(
 
     def get_users(self) -> dict[str, str]:
         try:
-            users = {}
+            users: dict[str, str] = {}
 
             query_string = "/Users"
-            response = self.query(query_string, "get")
+            response: list[dict[str, str | bool]] = self.query(query_string, "get")
 
             # If response is not empty
             if response:
                 for user in response:
-                    users[user["Name"]] = user["Id"]
+                    if isinstance(user["Name"], str) and isinstance(user["Id"], str):
+                        users[user["Name"]] = user["Id"]
 
             return users
         except Exception as e:
@@ -421,9 +425,11 @@ def get_user_library_watched(
             logger(traceback.format_exc(), 2)
             return {}
 
-    def get_watched(self, users, sync_libraries):
+    def get_watched(
+        self, users: dict[str, str], sync_libraries: list[str]
+    ) -> UsersWatched:
         try:
-            users_watched = {}
+            users_watched: UsersWatched = {}
             watched = []
 
             for user_name, user_id in users.items():
@@ -437,7 +443,7 @@ def get_watched(self, users, sync_libraries):
                     if library_title not in sync_libraries:
                         continue
 
-                    identifiers = {
+                    identifiers: dict[str, str] = {
                         "library_id": library_id,
                         "library_title": library_title,
                     }
@@ -454,8 +460,8 @@ def get_watched(self, users, sync_libraries):
                     if len(library["Items"]) == 0:
                         continue
 
-                    library_id = library["Identifiers"]["library_id"]
-                    library_title = library["Identifiers"]["library_title"]
+                    library_id: str = library["Identifiers"]["library_id"]
+                    library_title: str = library["Identifiers"]["library_title"]
 
                     # Get all library types excluding "Folder"
                     types = set(
diff --git a/src/library.py b/src/library.py
index 1f26d56..a4f9464 100644
--- a/src/library.py
+++ b/src/library.py
@@ -3,17 +3,18 @@
     match_list,
     search_mapping,
 )
+from src.custom_types import UsersWatched
 
 
 def check_skip_logic(
-    library_title,
-    library_type,
-    blacklist_library,
-    whitelist_library,
-    blacklist_library_type,
-    whitelist_library_type,
-    library_mapping=None,
-):
+    library_title: str,
+    library_type: str,
+    blacklist_library: list[str],
+    whitelist_library: list[str],
+    blacklist_library_type: list[str],
+    whitelist_library_type: list[str],
+    library_mapping: dict[str, str] | None = None,
+) -> str | None:
     skip_reason = None
     library_other = None
     if library_mapping:
@@ -48,11 +49,11 @@ def check_skip_logic(
 
 
 def check_blacklist_logic(
-    library_title,
-    library_type,
-    blacklist_library,
-    blacklist_library_type,
-    library_other=None,
+    library_title: str,
+    library_type: str,
+    blacklist_library: list[str],
+    blacklist_library_type: list[str],
+    library_other: str | None = None,
 ):
     skip_reason = None
     if isinstance(library_type, (list, tuple, set)):
@@ -84,11 +85,11 @@ def check_blacklist_logic(
 
 
 def check_whitelist_logic(
-    library_title,
-    library_type,
-    whitelist_library,
-    whitelist_library_type,
-    library_other=None,
+    library_title: str,
+    library_type: str,
+    whitelist_library: list[str],
+    whitelist_library_type: list[str],
+    library_other: str | None = None,
 ):
     skip_reason = None
     if len(whitelist_library_type) > 0:
@@ -131,14 +132,14 @@ def check_whitelist_logic(
 
 
 def filter_libaries(
-    server_libraries,
-    blacklist_library,
-    blacklist_library_type,
-    whitelist_library,
-    whitelist_library_type,
-    library_mapping=None,
-):
-    filtered_libaries = []
+    server_libraries: dict[str, str],
+    blacklist_library: list[str],
+    blacklist_library_type: list[str],
+    whitelist_library: list[str],
+    whitelist_library_type: list[str],
+    library_mapping: dict[str, str] | None = None,
+) -> list[str]:
+    filtered_libaries: list[str] = []
     for library in server_libraries:
         skip_reason = check_skip_logic(
             library,
@@ -162,12 +163,12 @@ def filter_libaries(
 def setup_libraries(
     server_1,
     server_2,
-    blacklist_library,
-    blacklist_library_type,
-    whitelist_library,
-    whitelist_library_type,
-    library_mapping=None,
-):
+    blacklist_library: list[str],
+    blacklist_library_type: list[str],
+    whitelist_library: list[str],
+    whitelist_library_type: list[str],
+    library_mapping: dict[str, str] | None = None,
+) -> tuple[list[str], list[str]]:
     server_1_libraries = server_1.get_libraries()
     server_2_libraries = server_2.get_libraries()
     logger(f"Server 1 libraries: {server_1_libraries}", 1)
@@ -201,14 +202,16 @@ def setup_libraries(
     return output_server_1_libaries, output_server_2_libaries
 
 
-def show_title_dict(user_list: dict):
+def show_title_dict(user_list: UsersWatched) -> dict[str, list[tuple[str] | None]]:
     try:
-        show_output_dict = {}
+        if not isinstance(user_list, dict):
+            return {}
+
+        show_output_dict: dict[str, list[tuple[str] | None]] = {}
         show_output_dict["locations"] = []
         show_counter = 0  # Initialize a counter for the current show position
 
-        show_output_keys = user_list.keys()
-        show_output_keys = [dict(x) for x in list(show_output_keys)]
+        show_output_keys = [dict(x) for x in list(user_list.keys())]
         for show_key in show_output_keys:
             for provider_key, provider_value in show_key.items():
                 # Skip title
@@ -233,9 +236,19 @@ def show_title_dict(user_list: dict):
         return {}
 
 
-def episode_title_dict(user_list: dict):
+def episode_title_dict(
+    user_list: UsersWatched,
+) -> dict[
+    str, list[str | bool | int | tuple[str] | dict[str, str | tuple[str]] | None]
+]:
     try:
-        episode_output_dict = {}
+        if not isinstance(user_list, dict):
+            return {}
+
+        episode_output_dict: dict[
+            str,
+            list[str | bool | int | tuple[str] | dict[str, str | tuple[str]] | None],
+        ] = {}
         episode_output_dict["completed"] = []
         episode_output_dict["time"] = []
         episode_output_dict["locations"] = []
@@ -293,12 +306,18 @@ def episode_title_dict(user_list: dict):
         return {}
 
 
-def movies_title_dict(user_list: dict):
+def movies_title_dict(
+    user_list: UsersWatched,
+) -> dict[str, list[str | bool | int | tuple[str] | None]]:
     try:
-        movies_output_dict = {}
-        movies_output_dict["completed"] = []
-        movies_output_dict["time"] = []
-        movies_output_dict["locations"] = []
+        if not isinstance(user_list, list):
+            return {}
+
+        movies_output_dict: dict[str, list[str | bool | int | tuple[str] | None]] = {
+            "completed": [],
+            "time": [],
+            "locations": [],
+        }
         movie_counter = 0  # Initialize a counter for the current movie position
 
         for movie in user_list:
@@ -325,7 +344,13 @@ def movies_title_dict(user_list: dict):
         return {}
 
 
-def generate_library_guids_dict(user_list: dict):
+def generate_library_guids_dict(
+    user_list: UsersWatched,
+) -> tuple[
+    dict[str, list[tuple[str] | None]],
+    dict[str, list[str | bool | int | tuple[str] | dict[str, str | tuple[str]] | None]],
+    dict[str, list[str | bool | int | tuple[str] | None]],
+]:
     # Handle the case where user_list is empty or does not contain the expected keys and values
     if not user_list:
         return {}, {}, {}
diff --git a/src/plex.py b/src/plex.py
index 116fcd7..82039c5 100644
--- a/src/plex.py
+++ b/src/plex.py
@@ -488,7 +488,7 @@ def get_users(self):
             logger(f"Plex: Failed to get users, Error: {e}", 2)
             raise Exception(e)
 
-    def get_libraries(self):
+    def get_libraries(self) -> dict[str, str]:
         try:
             output = {}