diff --git a/scripts/custom_tools/custom_tool.py b/scripts/custom_tools/custom_tool.py
index e6a814b..d5c6b87 100644
--- a/scripts/custom_tools/custom_tool.py
+++ b/scripts/custom_tools/custom_tool.py
@@ -14,10 +14,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "custom_tool"
-    HELP = "Test out-of-tree tool"
-    DESCRIPTION = "Test out-of-tree tool"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--echo", "-e", required=True, type=str)
diff --git a/scripts/custom_tools/registry.py b/scripts/custom_tools/registry.py
new file mode 100644
index 0000000..c2e3d15
--- /dev/null
+++ b/scripts/custom_tools/registry.py
@@ -0,0 +1,14 @@
+#!/usr/bin/env python3
+
+"""Example out-of-tree tool registry."""
+
+from infuse_iot.tools.registry import ToolSpec
+
+TOOLS = (
+    ToolSpec(
+        name="custom_tool",
+        help="Test out-of-tree tool",
+        description="Test out-of-tree tool",
+        module="custom_tool",
+    ),
+)
diff --git a/src/infuse_iot/app/main.py b/src/infuse_iot/app/main.py
index 23e895e..9108573 100644
--- a/src/infuse_iot/app/main.py
+++ b/src/infuse_iot/app/main.py
@@ -7,20 +7,29 @@
 __copyright__ = "Copyright 2024, Embeint Holdings Pty Ltd"
 
 import argparse
+import importlib
 import importlib.util
+import os
 import pathlib
-import pkgutil
 import sys
 import types
+from dataclasses import dataclass
+from typing import Any
 
 import argcomplete
+from argcomplete.lexers import split_line
 
-import infuse_iot.tools
-from infuse_iot.commands import InfuseCommand
 from infuse_iot.credentials import get_custom_tool_path
+from infuse_iot.tools.registry import TOOLS, ToolSpec, load_extension_tools
 from infuse_iot.version import __version__
 
 
+@dataclass(frozen=True)
+class RegisteredTool:
+    spec: ToolSpec
+    extension_path: pathlib.Path | None = None
+
+
 class InfuseApp:
     """The infuse 'application' object"""
 
@@ -28,56 +37,105 @@ def __init__(self):
         self.args = None
         self.parser = argparse.ArgumentParser("infuse")
         self.parser.add_argument("--version", action="version", version=f"{__version__}")
-        self._tools = {}
+        self._tools: dict[str, RegisteredTool] = {}
+        self._tool_parsers = {}
+        self._loaded_tools = set()
         # Load tools
         self._load_tools(self.parser)
-        # Handle CLI tab completion
-        argcomplete.autocomplete(self.parser)
 
     def run(self, argv):
         """Run the chosen subtool handler"""
+        argv = argv or sys.argv[1:]
+        self._load_selected_tool(argv)
+        self._load_selected_completion_tool()
+        # Handle CLI tab completion
+        argcomplete.autocomplete(self.parser)
         self.args = self.parser.parse_args(argv)
 
         tool = self.args.tool_class(self.args)
         tool.run()
 
-    def _load_from_module(self, parent_parser: argparse._SubParsersAction, module: types.ModuleType):
-        tool_cls: InfuseCommand = module.SubCommand
-        parser = parent_parser.add_parser(
-            tool_cls.NAME,
-            help=tool_cls.HELP,
-            description=tool_cls.DESCRIPTION,
-            formatter_class=argparse.RawDescriptionHelpFormatter,
-        )
+    def _load_from_module(
+        self,
+        parent_parser: argparse._SubParsersAction,
+        module: types.ModuleType,
+        parser: argparse.ArgumentParser | None = None,
+    ):
+        tool_cls: Any = module.SubCommand
+        if parser is None:
+            parser = parent_parser.add_parser(
+                tool_cls.NAME,
+                help=tool_cls.HELP,
+                description=tool_cls.DESCRIPTION,
+                formatter_class=argparse.RawDescriptionHelpFormatter,
+            )
         parser.set_defaults(tool_class=tool_cls)
         tool_cls.add_parser(parser)
 
+    def _load_selected_tool(self, argv: list[str]):
+        if not argv:
+            return
+
+        if argv[0] not in self._tools or argv[0] in self._loaded_tools:
+            return
+
+        tool = self._tools[argv[0]]
+        module = self._import_tool_module(tool)
+        self._load_from_module(self._tools_parser, module, self._tool_parsers[tool.spec.name])
+        self._loaded_tools.add(tool.spec.name)
+
+    def _import_tool_module(self, tool: RegisteredTool) -> types.ModuleType:
+        if tool.extension_path is None:
+            return importlib.import_module(tool.spec.module)
+
+        module_path = tool.extension_path / f"{tool.spec.module.replace('.', '/')}.py"
+        module_name = f"infuse_iot_custom_tools.{tool.spec.module}"
+        spec = importlib.util.spec_from_file_location(module_name, module_path)
+        if spec is None or spec.loader is None:
+            raise ImportError(f"Failed to import custom tool module: {module_path}")
+
+        module = importlib.util.module_from_spec(spec)
+        spec.loader.exec_module(module)
+        return module
+
+    def _load_selected_completion_tool(self):
+        if "_ARGCOMPLETE" not in os.environ:
+            return
+
+        comp_line = os.environ["COMP_LINE"]
+        comp_point = int(os.environ["COMP_POINT"])
+        _, _, _, comp_words, _ = split_line(comp_line, comp_point)
+
+        # Match argcomplete's own executable/module offset handling.
+        start = int(os.environ["_ARGCOMPLETE"]) - 1
+        parser_words = comp_words[start:]
+        if len(parser_words) > 1:
+            self._load_selected_tool(parser_words[1:])
+
     def _load_tools(self, parser: argparse.ArgumentParser):
-        tools_parser = parser.add_subparsers(title="commands", metavar="<command>", required=True)
+        self._tools_parser = parser.add_subparsers(title="commands", metavar="<command>", required=True)
 
-        # Iterate over local tools
-        for _, name, _ in pkgutil.walk_packages(infuse_iot.tools.__path__):
-            full_name = f"{infuse_iot.tools.__name__}.{name}"
-            module = importlib.import_module(full_name)
-            self._load_from_module(tools_parser, module)
+        # Register local tools without importing their implementation modules.
+        for tool in TOOLS:
+            self._register_tool(tool)
 
         # Load custom tools, if configured
         if extension_tools := get_custom_tool_path():
             extension_path = pathlib.Path(extension_tools)
-            for _, name, _ in pkgutil.walk_packages([extension_tools]):
-                full_name = f"{infuse_iot.tools.__name__}.{name}"
-                full_path = str(extension_path / f"{name}.py")
-                spec = importlib.util.spec_from_file_location(full_name, full_path)
-                if spec is None or spec.loader is None:
-                    continue
-                module = importlib.util.module_from_spec(spec)
-                try:
-                    spec.loader.exec_module(module)
-                except Exception as e:
-                    print(f"Failed to import '{name}': {str(e)}")
-                    continue
-                if hasattr(module, "SubCommand"):
-                    self._load_from_module(tools_parser, module)
+            for tool in load_extension_tools(extension_path):
+                self._register_tool(tool, extension_path)
+
+    def _register_tool(self, tool: ToolSpec, extension_path: pathlib.Path | None = None):
+        if tool.name in self._tools:
+            raise ValueError(f"Tool already registered: {tool.name}")
+
+        self._tools[tool.name] = RegisteredTool(tool, extension_path)
+        self._tool_parsers[tool.name] = self._tools_parser.add_parser(
+            tool.name,
+            help=tool.help,
+            description=tool.description,
+            formatter_class=argparse.RawDescriptionHelpFormatter,
+        )
 
 
 def main(argv=None):
diff --git a/src/infuse_iot/commands.py b/src/infuse_iot/commands.py
index 5c00516..0bb7db1 100644
--- a/src/infuse_iot/commands.py
+++ b/src/infuse_iot/commands.py
@@ -44,21 +44,6 @@ def __init__(self, args: argparse.Namespace):
     def run(self) -> None:
         """Run the subcommand"""
 
-    @property
-    @abstractmethod
-    def NAME(self) -> str:
-        pass
-
-    @property
-    @abstractmethod
-    def HELP(self) -> str:
-        pass
-
-    @property
-    @abstractmethod
-    def DESCRIPTION(self) -> str:
-        pass
-
 
 class InfuseRpcCommand:
     RPC_DATA_SEND: bool = False
diff --git a/src/infuse_iot/tools/annotate_events.py b/src/infuse_iot/tools/annotate_events.py
index 61408dc..9bc9dce 100644
--- a/src/infuse_iot/tools/annotate_events.py
+++ b/src/infuse_iot/tools/annotate_events.py
@@ -45,10 +45,6 @@ class TimeCheckType(enum.Enum):
 
 
 class SubCommand(InfuseCommand):
-    NAME = "annotate_events"
-    HELP = "Annotate events on Infuse Tags"
-    DESCRIPTION = "Save labelled event annotations live on Infuse Tags"
-
     _label_type: LabelType | Path
     _labels: list[str]
     _time_check: TimeCheckType
diff --git a/src/infuse_iot/tools/audio_record.py b/src/infuse_iot/tools/audio_record.py
index 00a75f4..e75996f 100644
--- a/src/infuse_iot/tools/audio_record.py
+++ b/src/infuse_iot/tools/audio_record.py
@@ -26,10 +26,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "audio_record"
-    HELP = "Record audio data to a file from TDF"
-    DESCRIPTION = "Record audio data to a file from TDF"
-
     def __init__(self, args):
         self._client = LocalClient(args.server_sock, 1.0)
         self._decoder = TDF()
diff --git a/src/infuse_iot/tools/auto_activate.py b/src/infuse_iot/tools/auto_activate.py
index 6389910..126c8fa 100644
--- a/src/infuse_iot/tools/auto_activate.py
+++ b/src/infuse_iot/tools/auto_activate.py
@@ -24,10 +24,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "auto_activate"
-    HELP = "Automatically activate/deactivate observed devices"
-    DESCRIPTION = "Automatically activate/deactivate observed devices"
-
     def __init__(self, args):
         self.app_ids = args.app
         self.active = args.active or False
diff --git a/src/infuse_iot/tools/bt_log.py b/src/infuse_iot/tools/bt_log.py
index 478a089..8bd554b 100644
--- a/src/infuse_iot/tools/bt_log.py
+++ b/src/infuse_iot/tools/bt_log.py
@@ -22,10 +22,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "bt_log"
-    HELP = "Connect to remote Bluetooth device serial logs"
-    DESCRIPTION = "Connect to remote Bluetooth device serial logs"
-
     def __init__(self, args):
         self._client = LocalClient(args.server_sock, 1.0)
         self._decoder = TDF()
diff --git a/src/infuse_iot/tools/cloud.py b/src/infuse_iot/tools/cloud.py
index 0bc1b44..f931145 100644
--- a/src/infuse_iot/tools/cloud.py
+++ b/src/infuse_iot/tools/cloud.py
@@ -815,10 +815,6 @@ def upload_diffs_from_application(
 
 
 class SubCommand(InfuseCommand):
-    NAME = "cloud"
-    HELP = "Infuse-IoT cloud interaction"
-    DESCRIPTION = "Infuse-IoT cloud interaction"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--api-key", type=str, help="Cloud API key to use instead of stored credentials")
diff --git a/src/infuse_iot/tools/credentials.py b/src/infuse_iot/tools/credentials.py
index 4f42fd6..01dc953 100644
--- a/src/infuse_iot/tools/credentials.py
+++ b/src/infuse_iot/tools/credentials.py
@@ -9,14 +9,11 @@
 
 from infuse_iot import credentials
 from infuse_iot.commands import InfuseCommand
+from infuse_iot.tools.registry import load_extension_tools
 from infuse_iot.util.argparse import ValidDir, ValidFile
 
 
 class SubCommand(InfuseCommand):
-    NAME = "credentials"
-    HELP = "Manage Infuse-IoT credentials"
-    DESCRIPTION = "Manage Infuse-IoT credentials"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--api-key", type=str, help="Set Infuse-IoT API key")
@@ -44,6 +41,7 @@ def run(self):
             network_info = yaml.safe_load(content)
             credentials.save_network(network_info["id"], content)
         if self.args.custom_tools:
+            load_extension_tools(self.args.custom_tools)
             credentials.set_custom_tool_path(str(self.args.custom_tools.absolute()))
         if self.args.custom_definitions:
             credentials.set_custom_definitions_path(str(self.args.custom_definitions.absolute()))
diff --git a/src/infuse_iot/tools/csv_annotate.py b/src/infuse_iot/tools/csv_annotate.py
index c39b4ef..bafeeb2 100644
--- a/src/infuse_iot/tools/csv_annotate.py
+++ b/src/infuse_iot/tools/csv_annotate.py
@@ -10,10 +10,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "csv_annotate"
-    HELP = "Annotate CSV data"
-    DESCRIPTION = "Annotate CSV data"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--file", "-f", required=True, type=ValidFile)
diff --git a/src/infuse_iot/tools/csv_plot.py b/src/infuse_iot/tools/csv_plot.py
index 199dcc3..e58f965 100644
--- a/src/infuse_iot/tools/csv_plot.py
+++ b/src/infuse_iot/tools/csv_plot.py
@@ -10,10 +10,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "csv_plot"
-    HELP = "Plot CSV data"
-    DESCRIPTION = "Plot CSV data"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument(
diff --git a/src/infuse_iot/tools/data_logger_sync.py b/src/infuse_iot/tools/data_logger_sync.py
index 54dc5c5..f7be1a2 100644
--- a/src/infuse_iot/tools/data_logger_sync.py
+++ b/src/infuse_iot/tools/data_logger_sync.py
@@ -59,10 +59,6 @@ def append_data(self, data: bytes):
 
 
 class SubCommand(InfuseCommand):
-    NAME = "data_logger_sync"
-    HELP = "Synchronise data logger state from remote devices"
-    DESCRIPTION = "Synchronise data logger state from remote devices"
-
     def __init__(self, args):
         self._client = LocalClient(args.server_sock, 1.0)
         self._min_rssi: int | None = args.rssi
diff --git a/src/infuse_iot/tools/gateway.py b/src/infuse_iot/tools/gateway.py
index ccad1b1..ab6041f 100644
--- a/src/infuse_iot/tools/gateway.py
+++ b/src/infuse_iot/tools/gateway.py
@@ -451,10 +451,6 @@ def _iter(self) -> None:
 
 
 class SubCommand(InfuseCommand):
-    NAME = "gateway"
-    HELP = "Connect to a local gateway device"
-    DESCRIPTION = "Connect to a gateway device over serial and route commands to Bluetooth devices"
-
     @classmethod
     def add_parser(cls, parser):
         # COM ports are not valid files
diff --git a/src/infuse_iot/tools/localhost.py b/src/infuse_iot/tools/localhost.py
index c530a7d..d683e07 100644
--- a/src/infuse_iot/tools/localhost.py
+++ b/src/infuse_iot/tools/localhost.py
@@ -35,10 +35,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "localhost"
-    HELP = "Run a local server for TDF viewing"
-    DESCRIPTION = "Run a local server for TDF viewing"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--port", "-p", type=int, default=8080, help="Port number for localhost server")
diff --git a/src/infuse_iot/tools/native_bt.py b/src/infuse_iot/tools/native_bt.py
index f1008d2..26e507b 100644
--- a/src/infuse_iot/tools/native_bt.py
+++ b/src/infuse_iot/tools/native_bt.py
@@ -257,10 +257,6 @@ def connection_lost(self, exc):
 
 
 class SubCommand(InfuseCommand):
-    NAME = "native_bt"
-    HELP = "Native Bluetooth gateway"
-    DESCRIPTION = "Use the local Bluetooth adapter for Bluetooth interaction"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--root", type=ValidFile, help="Root identity certificate to use instead of cloud")
diff --git a/src/infuse_iot/tools/ota_upgrade.py b/src/infuse_iot/tools/ota_upgrade.py
index 1d9b59b..556ca2e 100644
--- a/src/infuse_iot/tools/ota_upgrade.py
+++ b/src/infuse_iot/tools/ota_upgrade.py
@@ -36,10 +36,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "ota_upgrade"
-    HELP = "Automatically OTA upgrade observed devices"
-    DESCRIPTION = "Automatically OTA upgrade observed devices"
-
     def __init__(self, args):
         self._client = LocalClient(args.server_sock, 1.0)
         self._conn_timeout = args.conn_timeout
diff --git a/src/infuse_iot/tools/provision.py b/src/infuse_iot/tools/provision.py
index 3a6e8ee..dd74a44 100644
--- a/src/infuse_iot/tools/provision.py
+++ b/src/infuse_iot/tools/provision.py
@@ -26,10 +26,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "provision"
-    HELP = "Provision device on Infuse Cloud"
-    DESCRIPTION = "Provision device on Infuse Cloud"
-
     @classmethod
     def add_parser(cls, parser):
         vendor_group = parser.add_mutually_exclusive_group(required=True)
diff --git a/src/infuse_iot/tools/registry.py b/src/infuse_iot/tools/registry.py
new file mode 100644
index 0000000..1257082
--- /dev/null
+++ b/src/infuse_iot/tools/registry.py
@@ -0,0 +1,187 @@
+#!/usr/bin/env python3
+
+"""Tool registry definitions."""
+
+import importlib.util
+import pathlib
+import types
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class ToolSpec:
+    """Lightweight command metadata for parser construction."""
+
+    name: str
+    help: str
+    description: str
+    module: str
+
+
+def _load_registry_module(path: pathlib.Path) -> types.ModuleType:
+    registry_path = path / "registry.py"
+    if not registry_path.exists():
+        raise FileNotFoundError(f"Custom tools registry does not exist: {registry_path}")
+
+    spec = importlib.util.spec_from_file_location("infuse_iot_custom_tools.registry", registry_path)
+    if spec is None or spec.loader is None:
+        raise ValueError(f"Failed to load custom tools registry: {registry_path}")
+
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def load_extension_tools(path: str | pathlib.Path) -> tuple[ToolSpec, ...]:
+    """Load and validate ToolSpec entries from an extension tool directory."""
+    extension_path = pathlib.Path(path)
+    module = _load_registry_module(extension_path)
+
+    if not hasattr(module, "TOOLS"):
+        raise ValueError(f"Custom tools registry {extension_path / 'registry.py'} does not define TOOLS")
+
+    tools = module.TOOLS
+    if not isinstance(tools, (list, tuple)):
+        raise TypeError("Custom tools registry TOOLS must be a list or tuple of ToolSpec entries")
+
+    names = set()
+    validated_tools = []
+    for tool in tools:
+        if not isinstance(tool, ToolSpec):
+            raise TypeError("Custom tools registry TOOLS must contain only ToolSpec entries")
+        if tool.name in names:
+            raise ValueError(f"Duplicate custom tool name: {tool.name}")
+        names.add(tool.name)
+        if not tool.name:
+            raise ValueError("Custom tool name cannot be empty")
+        if not tool.help:
+            raise ValueError(f"Custom tool {tool.name} help cannot be empty")
+        if not tool.description:
+            raise ValueError(f"Custom tool {tool.name} description cannot be empty")
+        if not tool.module:
+            raise ValueError(f"Custom tool {tool.name} module cannot be empty")
+
+        module_path = extension_path / f"{tool.module.replace('.', '/')}.py"
+        if not module_path.exists():
+            raise FileNotFoundError(f"Custom tool module does not exist: {module_path}")
+        validated_tools.append(tool)
+
+    return tuple(validated_tools)
+
+
+TOOLS = (
+    ToolSpec(
+        name="annotate_events",
+        help="Annotate events on Infuse Tags",
+        description="Save labelled event annotations live on Infuse Tags",
+        module="infuse_iot.tools.annotate_events",
+    ),
+    ToolSpec(
+        name="audio_record",
+        help="Record audio data to a file from TDF",
+        description="Record audio data to a file from TDF",
+        module="infuse_iot.tools.audio_record",
+    ),
+    ToolSpec(
+        name="auto_activate",
+        help="Automatically activate/deactivate observed devices",
+        description="Automatically activate/deactivate observed devices",
+        module="infuse_iot.tools.auto_activate",
+    ),
+    ToolSpec(
+        name="bt_log",
+        help="Connect to remote Bluetooth device serial logs",
+        description="Connect to remote Bluetooth device serial logs",
+        module="infuse_iot.tools.bt_log",
+    ),
+    ToolSpec(
+        name="cloud",
+        help="Infuse-IoT cloud interaction",
+        description="Infuse-IoT cloud interaction",
+        module="infuse_iot.tools.cloud",
+    ),
+    ToolSpec(
+        name="credentials",
+        help="Manage Infuse-IoT credentials",
+        description="Manage Infuse-IoT credentials",
+        module="infuse_iot.tools.credentials",
+    ),
+    ToolSpec(
+        name="csv_annotate",
+        help="Annotate CSV data",
+        description="Annotate CSV data",
+        module="infuse_iot.tools.csv_annotate",
+    ),
+    ToolSpec(
+        name="csv_plot",
+        help="Plot CSV data",
+        description="Plot CSV data",
+        module="infuse_iot.tools.csv_plot",
+    ),
+    ToolSpec(
+        name="data_logger_sync",
+        help="Synchronise data logger state from remote devices",
+        description="Synchronise data logger state from remote devices",
+        module="infuse_iot.tools.data_logger_sync",
+    ),
+    ToolSpec(
+        name="gateway",
+        help="Connect to a local gateway device",
+        description="Connect to a gateway device over serial and route commands to Bluetooth devices",
+        module="infuse_iot.tools.gateway",
+    ),
+    ToolSpec(
+        name="localhost",
+        help="Run a local server for TDF viewing",
+        description="Run a local server for TDF viewing",
+        module="infuse_iot.tools.localhost",
+    ),
+    ToolSpec(
+        name="native_bt",
+        help="Native Bluetooth gateway",
+        description="Use the local Bluetooth adapter for Bluetooth interaction",
+        module="infuse_iot.tools.native_bt",
+    ),
+    ToolSpec(
+        name="ota_upgrade",
+        help="Automatically OTA upgrade observed devices",
+        description="Automatically OTA upgrade observed devices",
+        module="infuse_iot.tools.ota_upgrade",
+    ),
+    ToolSpec(
+        name="provision",
+        help="Provision device on Infuse Cloud",
+        description="Provision device on Infuse Cloud",
+        module="infuse_iot.tools.provision",
+    ),
+    ToolSpec(
+        name="rpc",
+        help="Run remote procedure calls on devices",
+        description="Run remote procedure calls on devices",
+        module="infuse_iot.tools.rpc",
+    ),
+    ToolSpec(
+        name="rpc_cloud",
+        help="Manage remote procedure calls through Infuse-IoT cloud",
+        description="Manage remote procedure calls through Infuse-IoT cloud",
+        module="infuse_iot.tools.rpc_cloud",
+    ),
+    ToolSpec(
+        name="serial_throughput",
+        help="Test serial throughput to local gateway",
+        description="Test serial throughput to local gateway",
+        module="infuse_iot.tools.serial_throughput",
+    ),
+    ToolSpec(
+        name="tdf_csv",
+        help="Save received TDFs in CSV files",
+        description="Save received TDFs in CSV files",
+        module="infuse_iot.tools.tdf_csv",
+    ),
+    ToolSpec(
+        name="tdf_list",
+        help="Display received TDFs in a list",
+        description="Display received TDFs in a list",
+        module="infuse_iot.tools.tdf_list",
+    ),
+)
diff --git a/src/infuse_iot/tools/rpc.py b/src/infuse_iot/tools/rpc.py
index 59dd0d4..e9e6036 100644
--- a/src/infuse_iot/tools/rpc.py
+++ b/src/infuse_iot/tools/rpc.py
@@ -25,10 +25,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "rpc"
-    HELP = "Run remote procedure calls on devices"
-    DESCRIPTION = "Run remote procedure calls on devices"
-
     @classmethod
     def add_parser(cls, parser):
         addr_group = parser.add_mutually_exclusive_group(required=True)
diff --git a/src/infuse_iot/tools/rpc_cloud.py b/src/infuse_iot/tools/rpc_cloud.py
index 6e6bb91..4eecc01 100644
--- a/src/infuse_iot/tools/rpc_cloud.py
+++ b/src/infuse_iot/tools/rpc_cloud.py
@@ -27,10 +27,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "rpc_cloud"
-    HELP = "Manage remote procedure calls through Infuse-IoT cloud"
-    DESCRIPTION = "Manage remote procedure calls through Infuse-IoT cloud"
-
     @classmethod
     def add_parser(cls, parser):
         subparser = parser.add_subparsers(title="commands", metavar="<command>", required=True)
diff --git a/src/infuse_iot/tools/serial_throughput.py b/src/infuse_iot/tools/serial_throughput.py
index 2d8f3da..93a00ae 100644
--- a/src/infuse_iot/tools/serial_throughput.py
+++ b/src/infuse_iot/tools/serial_throughput.py
@@ -25,10 +25,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "serial_throughput"
-    HELP = "Test serial throughput to local gateway"
-    DESCRIPTION = "Test serial throughput to local gateway"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument(
diff --git a/src/infuse_iot/tools/tdf_csv.py b/src/infuse_iot/tools/tdf_csv.py
index 1d90bbc..29e0964 100644
--- a/src/infuse_iot/tools/tdf_csv.py
+++ b/src/infuse_iot/tools/tdf_csv.py
@@ -25,10 +25,6 @@ def _to_str(unix_time: float) -> str:
 
 
 class SubCommand(InfuseCommand):
-    NAME = "tdf_csv"
-    HELP = "Save received TDFs in CSV files"
-    DESCRIPTION = "Save received TDFs in CSV files"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--unix", action="store_true", help="Save timestamps as unix")
diff --git a/src/infuse_iot/tools/tdf_list.py b/src/infuse_iot/tools/tdf_list.py
index 09d2e08..c82f582 100644
--- a/src/infuse_iot/tools/tdf_list.py
+++ b/src/infuse_iot/tools/tdf_list.py
@@ -23,10 +23,6 @@
 
 
 class SubCommand(InfuseCommand):
-    NAME = "tdf_list"
-    HELP = "Display received TDFs in a list"
-    DESCRIPTION = "Display received TDFs in a list"
-
     @classmethod
     def add_parser(cls, parser):
         parser.add_argument("--array-all", action="store_true", help="Display all array values, not just the last")
diff --git a/tests/test_custom_tools.py b/tests/test_custom_tools.py
index 4ba396e..8cd0a80 100644
--- a/tests/test_custom_tools.py
+++ b/tests/test_custom_tools.py
@@ -3,10 +3,12 @@
 import os
 import pathlib
 import subprocess
+import sys
 
 import pytest
 
 import infuse_iot.credentials as cred
+from infuse_iot.app.main import InfuseApp
 
 assert "TOXTEMPDIR" in os.environ, "you must run these tests using tox"
 
@@ -23,7 +25,7 @@ def test_custom_tool_integration():
     with pytest.raises(subprocess.CalledProcessError):
         subprocess.check_output(["infuse", "custom_tool", "--echo", echo_string])
 
-    custom_tools_path = pathlib.Path(__file__).parent.parent / 'scripts' / 'custom_tools'
+    custom_tools_path = pathlib.Path(__file__).parent.parent / "scripts" / "custom_tools"
 
     subprocess.check_output(["infuse", "credentials", "--custom-tools", str(custom_tools_path)])
 
@@ -34,3 +36,29 @@ def test_custom_tool_integration():
 
     with pytest.raises(subprocess.CalledProcessError):
         subprocess.check_output(["infuse", "custom_tool", "--echo", echo_string])
+
+
+def test_custom_tool_path_requires_registry(tmp_path):
+    with pytest.raises(subprocess.CalledProcessError):
+        subprocess.check_output(["infuse", "credentials", "--custom-tools", str(tmp_path)])
+
+
+def test_extension_tool_registry_loading():
+    custom_tools_path = pathlib.Path(__file__).parent.parent / "scripts" / "custom_tools"
+
+    try:
+        cred.set_custom_tool_path(str(custom_tools_path))
+        sys.modules.pop("infuse_iot_custom_tools.custom_tool", None)
+
+        app = InfuseApp()
+
+        assert "custom_tool" in app._tools
+        assert app._tools["custom_tool"].spec.module == "custom_tool"
+        assert "custom_tool" not in app._loaded_tools
+        assert "infuse_iot_custom_tools.custom_tool" not in sys.modules
+
+        app._load_selected_tool(["custom_tool", "--echo", "test_string"])
+
+        assert "custom_tool" in app._loaded_tools
+    finally:
+        cred.delete_custom_tool_path()
diff --git a/tests/test_help.py b/tests/test_help.py
index 9e9d9e2..7322e97 100644
--- a/tests/test_help.py
+++ b/tests/test_help.py
@@ -16,3 +16,18 @@ def test_help():
 
     subprocess.check_output([sys.executable, "-m", "infuse_iot", "--help"])
     subprocess.check_output(["infuse", "--help"])
+
+
+def test_completion_loads_selected_tool(monkeypatch):
+    from infuse_iot.app.main import InfuseApp
+
+    command_line = "infuse credentials --api"
+    monkeypatch.setenv("COMP_LINE", command_line)
+    monkeypatch.setenv("COMP_POINT", str(len(command_line)))
+    monkeypatch.setenv("_ARGCOMPLETE", "1")
+
+    app = InfuseApp()
+    assert "infuse_iot.tools.credentials" not in sys.modules
+
+    app._load_selected_completion_tool()
+    assert "infuse_iot.tools.credentials" in sys.modules