diff --git a/bemani/client/base.py b/bemani/client/base.py
index 7ad231f..6bfa54f 100644
--- a/bemani/client/base.py
+++ b/bemani/client/base.py
@@ -1,5 +1,6 @@
 import time
 from typing import Optional, Dict, List, Tuple, Any
+from typing_extensions import Final
 
 from bemani.client.common import random_hex_string
 from bemani.client.protocol import ClientProtocol
@@ -13,13 +14,13 @@ class BaseClient:
     and verify some basic packets that are always expected to work.
     """
 
-    CARD_OK = 0
-    CARD_NEW = 112
-    CARD_BAD_PIN = 116
-    CARD_NOT_ALLOWED = 110
+    CARD_OK: Final[int] = 0
+    CARD_NEW: Final[int] = 112
+    CARD_BAD_PIN: Final[int] = 116
+    CARD_NOT_ALLOWED: Final[int] = 110
 
-    CORRECT_PASSWORD = '1234'
-    WRONG_PASSWORD = '4321'
+    CORRECT_PASSWORD: Final[str] = '1234'
+    WRONG_PASSWORD: Final[str] = '4321'
 
     def __init__(self, proto: ClientProtocol, pcbid: str, config: Dict[str, Any]) -> None:
         self.__proto = proto
diff --git a/bemani/data/api/client.py b/bemani/data/api/client.py
index 6a56331..aeb0122 100644
--- a/bemani/data/api/client.py
+++ b/bemani/data/api/client.py
@@ -1,6 +1,7 @@
 import json
 import requests
 from typing import Tuple, Dict, List, Any, Optional
+from typing_extensions import Final
 
 from bemani.common import APIConstants, GameConstants, VersionConstants, DBConstants, ValidatedDict
 
@@ -34,7 +35,7 @@ class APIClient:
     A client that fully speaks BEMAPI and can pull information from a remote server.
     """
 
-    API_VERSION = 'v1'
+    API_VERSION: Final[str] = 'v1'
 
     def __init__(self, base_uri: str, token: str, allow_stats: bool, allow_scores: bool) -> None:
         self.base_uri = base_uri
diff --git a/bemani/data/mysql/base.py b/bemani/data/mysql/base.py
index 3614582..5f60c40 100644
--- a/bemani/data/mysql/base.py
+++ b/bemani/data/mysql/base.py
@@ -1,6 +1,7 @@
 import json
 import random
 from typing import Dict, Any, Optional
+from typing_extensions import Final
 
 from bemani.common import Time
 from bemani.data.config import Config
@@ -38,7 +39,7 @@ class _BytesEncoder(json.JSONEncoder):
 
 class BaseData:
 
-    SESSION_LENGTH = 32
+    SESSION_LENGTH: Final[int] = 32
 
     def __init__(self, config: Config, conn: Connection) -> None:
         """
diff --git a/bemani/data/mysql/user.py b/bemani/data/mysql/user.py
index 1b88b39..c35c914 100644
--- a/bemani/data/mysql/user.py
+++ b/bemani/data/mysql/user.py
@@ -4,6 +4,7 @@ from sqlalchemy.types import String, Integer, JSON  # type: ignore
 from sqlalchemy.dialects.mysql import BIGINT as BigInteger  # type: ignore
 from sqlalchemy.exc import IntegrityError  # type: ignore
 from typing import Optional, Dict, List, Tuple, Any
+from typing_extensions import Final
 from passlib.hash import pbkdf2_sha512  # type: ignore
 
 from bemani.common import ValidatedDict, Profile, GameConstants, Time
@@ -165,7 +166,7 @@ class AccountCreationException(Exception):
 
 class UserData(BaseData):
 
-    REF_ID_LENGTH = 16
+    REF_ID_LENGTH: Final[int] = 16
 
     def from_cardid(self, cardid: str) -> Optional[UserID]:
         """
diff --git a/bemani/format/iidxchart.py b/bemani/format/iidxchart.py
index 28a1cf7..f79bfa4 100644
--- a/bemani/format/iidxchart.py
+++ b/bemani/format/iidxchart.py
@@ -1,5 +1,6 @@
 import struct
 from typing import List, Optional, Tuple
+from typing_extensions import Final
 
 
 class IIDXChart:
@@ -11,7 +12,7 @@ class IIDXChart:
     clear ranks for IIDX.
     """
 
-    CHART_POSITIONS = [1, 0, 2, 7, 6, 8]
+    CHART_POSITIONS: Final[List[int]] = [1, 0, 2, 7, 6, 8]
 
     def __init__(self, data: bytes) -> None:
         self.__bpm_min: Optional[int] = None
diff --git a/bemani/sniff/sniff.py b/bemani/sniff/sniff.py
index 3057bb7..d7ab641 100644
--- a/bemani/sniff/sniff.py
+++ b/bemani/sniff/sniff.py
@@ -1,6 +1,7 @@
 import socket
 import struct
 from typing import Any, Dict, List, Optional, Tuple
+from typing_extensions import Final
 
 
 class InvalidPacketException(Exception):
@@ -23,8 +24,8 @@ class TCPStream:
     SYN -> SYNACK -> ACK flow followed by some data followed by a FIN -> FINACK -> ACK
     flow. Luckily, this is exactly what most HTTP requests look like.
     """
-    INBOUND = 'inbound'
-    OUTBOUND = 'outbound'
+    INBOUND: Final[str] = 'inbound'
+    OUTBOUND: Final[str] = 'outbound'
 
     def __init__(self, packet: Dict[str, Any]) -> None:
         """
@@ -196,10 +197,10 @@ class Sniffer:
     A generic python sniffer. Listens to all raw traffic on the machine and parses packets
     down to TCP chunks to be reassembled.
     """
-    RECEIVE_SIZE = 1048576
-    ETH_HEADER_LENGTH = 14
-    IP_HEADER_LENGTH = 20
-    TCP_HEADER_LENGTH = 20
+    RECEIVE_SIZE: Final[int] = 1048576
+    ETH_HEADER_LENGTH: Final[int] = 14
+    IP_HEADER_LENGTH: Final[int] = 20
+    TCP_HEADER_LENGTH: Final[int] = 20
 
     def __init__(self, address: Optional[str]=None, port: Optional[int]=None) -> None:
         """