diff --git a/apps/console.py b/apps/console.py
index b7c30c77..80df6a61 100644
--- a/apps/console.py
+++ b/apps/console.py
@@ -24,6 +24,7 @@ import logging
 import os
 import random
 import re
+from typing import Optional
 from collections import OrderedDict
 
 import click
@@ -58,6 +59,7 @@ from bumble.device import ConnectionParametersPreferences, Device, Connection, P
 from bumble.utils import AsyncRunner
 from bumble.transport import open_transport_or_link
 from bumble.gatt import Characteristic, Service, CharacteristicDeclaration, Descriptor
+from bumble.gatt_client import CharacteristicProxy
 from bumble.hci import (
     HCI_Constant,
     HCI_LE_1M_PHY,
@@ -119,6 +121,8 @@ def parse_phys(phys):
 # Console App
 # -----------------------------------------------------------------------------
 class ConsoleApp:
+    connected_peer: Optional[Peer]
+
     def __init__(self):
         self.known_addresses = set()
         self.known_attributes = []
@@ -490,7 +494,9 @@ class ConsoleApp:
 
         self.show_attributes(attributes)
 
-    def find_characteristic(self, param):
+    def find_characteristic(self, param) -> Optional[CharacteristicProxy]:
+        if not self.connected_peer:
+            return None
         parts = param.split('.')
         if len(parts) == 2:
             service_uuid = UUID(parts[0]) if parts[0] != '*' else None
diff --git a/bumble/att.py b/bumble/att.py
index 89ceb113..9387a59a 100644
--- a/bumble/att.py
+++ b/bumble/att.py
@@ -28,8 +28,8 @@ import struct
 from pyee import EventEmitter
 from typing import Dict, Type, TYPE_CHECKING
 
-from bumble.core import UUID, name_or_number, get_dict_key_by_value
-from bumble.hci import HCI_Object, key_with_value
+from bumble.core import UUID, name_or_number, get_dict_key_by_value, ProtocolError
+from bumble.hci import HCI_Object, key_with_value, HCI_Constant
 from bumble.colors import color
 
 if TYPE_CHECKING:
@@ -185,13 +185,18 @@ UUID_2_FIELD_SPEC    = lambda x, y: UUID.parse_uuid_2(x, y)  # noqa: E731
 # -----------------------------------------------------------------------------
 # Exceptions
 # -----------------------------------------------------------------------------
-class ATT_Error(Exception):
-    def __init__(self, error_code, att_handle=0x0000):
-        self.error_code = error_code
+class ATT_Error(ProtocolError):
+    def __init__(self, error_code, att_handle=0x0000, message=''):
+        super().__init__(
+            error_code,
+            error_namespace='att',
+            error_name=ATT_PDU.error_name(self.error_code),
+        )
         self.att_handle = att_handle
+        self.message = message
 
     def __str__(self):
-        return f'ATT_Error({ATT_PDU.error_name(self.error_code)})'
+        return f'ATT_Error(error={self.error_name}, handle={self.att_handle:04X}): {self.message}'
 
 
 # -----------------------------------------------------------------------------
diff --git a/bumble/gatt_client.py b/bumble/gatt_client.py
index 2fd75736..25add180 100644
--- a/bumble/gatt_client.py
+++ b/bumble/gatt_client.py
@@ -23,9 +23,11 @@
 # -----------------------------------------------------------------------------
 # Imports
 # -----------------------------------------------------------------------------
+from __future__ import annotations
 import asyncio
 import logging
 import struct
+from typing import List, Optional
 
 from pyee import EventEmitter
 
@@ -50,6 +52,7 @@ from .att import (
     ATT_Read_Request,
     ATT_Write_Command,
     ATT_Write_Request,
+    ATT_Error,
 )
 from . import core
 from .core import UUID, InvalidStateError, ProtocolError
@@ -59,6 +62,7 @@ from .gatt import (
     GATT_PRIMARY_SERVICE_ATTRIBUTE_TYPE,
     GATT_REQUEST_TIMEOUT,
     GATT_SECONDARY_SERVICE_ATTRIBUTE_TYPE,
+    Service,
     Characteristic,
     ClientCharacteristicConfigurationBits,
 )
@@ -73,6 +77,8 @@ logger = logging.getLogger(__name__)
 # Proxies
 # -----------------------------------------------------------------------------
 class AttributeProxy(EventEmitter):
+    client: Client
+
     def __init__(self, client, handle, end_group_handle, attribute_type):
         EventEmitter.__init__(self)
         self.client = client
@@ -101,6 +107,9 @@ class AttributeProxy(EventEmitter):
 
 
 class ServiceProxy(AttributeProxy):
+    uuid: UUID
+    characteristics: List[CharacteristicProxy]
+
     @staticmethod
     def from_client(service_class, client, service_uuid):
         # The service and its characteristics are considered to have already been
@@ -130,6 +139,8 @@ class ServiceProxy(AttributeProxy):
 
 
 class CharacteristicProxy(AttributeProxy):
+    descriptors: List[DescriptorProxy]
+
     def __init__(self, client, handle, end_group_handle, uuid, properties):
         super().__init__(client, handle, end_group_handle, uuid)
         self.uuid = uuid
@@ -201,6 +212,8 @@ class ProfileServiceProxy:
 # GATT Client
 # -----------------------------------------------------------------------------
 class Client:
+    services: List[ServiceProxy]
+
     def __init__(self, connection):
         self.connection = connection
         self.mtu_exchange_done = False
@@ -306,7 +319,7 @@ class Client:
         if not already_known:
             self.services.append(service)
 
-    async def discover_services(self, uuids=None):
+    async def discover_services(self, uuids=None) -> List[ServiceProxy]:
         '''
         See Vol 3, Part G - 4.4.1 Discover All Primary Services
         '''
@@ -332,8 +345,10 @@ class Client:
                         '!!! unexpected error while discovering services: '
                         f'{HCI_Constant.error_name(response.error_code)}'
                     )
-                    # TODO raise appropriate exception
-                    return
+                    raise ATT_Error(
+                        error_code=response.error_code,
+                        message='Unexpected error while discovering services',
+                    )
                 break
 
             for (
@@ -349,7 +364,7 @@ class Client:
                     logger.warning(
                         f'bogus handle values: {attribute_handle} {end_group_handle}'
                     )
-                    return
+                    return []
 
                 # Create a service proxy for this service
                 service = ServiceProxy(
@@ -452,7 +467,9 @@ class Client:
         # TODO
         return []
 
-    async def discover_characteristics(self, uuids, service):
+    async def discover_characteristics(
+        self, uuids, service: Optional[ServiceProxy]
+    ) -> List[CharacteristicProxy]:
         '''
         See Vol 3, Part G - 4.6.1 Discover All Characteristics of a Service and 4.6.2
         Discover Characteristics by UUID
@@ -465,12 +482,12 @@ class Client:
         services = [service] if service else self.services
 
         # Perform characteristic discovery for each service
-        discovered_characteristics = []
+        discovered_characteristics: List[CharacteristicProxy] = []
         for service in services:
             starting_handle = service.handle
             ending_handle = service.end_group_handle
 
-            characteristics = []
+            characteristics: List[CharacteristicProxy] = []
             while starting_handle <= ending_handle:
                 response = await self.send_request(
                     ATT_Read_By_Type_Request(
@@ -491,8 +508,10 @@ class Client:
                             '!!! unexpected error while discovering characteristics: '
                             f'{HCI_Constant.error_name(response.error_code)}'
                         )
-                        # TODO raise appropriate exception
-                        return
+                        raise ATT_Error(
+                            error_code=response.error_code,
+                            message='Unexpected error while discovering characteristics',
+                        )
                     break
 
                 # Stop if for some reason the list was empty
@@ -535,8 +554,11 @@ class Client:
         return discovered_characteristics
 
     async def discover_descriptors(
-        self, characteristic=None, start_handle=None, end_handle=None
-    ):
+        self,
+        characteristic: Optional[CharacteristicProxy] = None,
+        start_handle=None,
+        end_handle=None,
+    ) -> List[DescriptorProxy]:
         '''
         See Vol 3, Part G - 4.7.1 Discover All Characteristic Descriptors
         '''
@@ -549,7 +571,7 @@ class Client:
         else:
             return []
 
-        descriptors = []
+        descriptors: List[DescriptorProxy] = []
         while starting_handle <= ending_handle:
             response = await self.send_request(
                 ATT_Find_Information_Request(