diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 427575c..4d29491 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,6 +20,7 @@ jobs:
       - run: uv sync --all-extras --dev
       - run: uv run ruff check
       - run: uv run ruff format --check
+      - run: uv run pyrefly check
 
   docs:
     runs-on: ubuntu-latest
diff --git a/monitorcontrol/monitorcontrol.py b/monitorcontrol/monitorcontrol.py
index ebbb5cb..166f40c 100644
--- a/monitorcontrol/monitorcontrol.py
+++ b/monitorcontrol/monitorcontrol.py
@@ -458,7 +458,7 @@ def set_input_source(self, value: Union[int, str, InputSource]):
         self._set_vcp_feature(vcp_codes.input_select, mode_value)
 
 
-def get_vcps() -> List[Type[vcp.VCP]]:
+def get_vcps() -> List[vcp.VCP]:
     """
     Discovers virtual control panels.
 
@@ -587,7 +587,8 @@ def _parse_capabilities(caps_str: str) -> dict:
     """
     Converts the capabilities string into a nice dict
     """
-    caps_dict = {
+
+    caps_dict: dict[str, str | list | dict[int, dict]] = {
         # Used to specify the protocol class
         "prot": "",
         # Identifies the type of display
@@ -595,10 +596,10 @@ def _parse_capabilities(caps_str: str) -> dict:
         # The display model number
         "model": "",
         # A list of supported VCP codes. Somehow not the same as "vcp"
-        "cmds": "",
+        "cmds": {},
         # A list of supported VCP codes with a list of supported values
         # for each nc code
-        "vcp": "",
+        "vcp": {},
         # undocumented
         "mswhql": "",
         # undocumented
@@ -612,12 +613,13 @@ def _parse_capabilities(caps_str: str) -> dict:
         # Alternate name to be used for control
         "vcpname": "",
         # Parsed input sources into text. Not part of capabilities string.
-        "inputs": "",
+        "inputs": [],
         # Parsed color presets into text. Not part of capabilities string.
         "color_presets": "",
     }
 
     for key in caps_dict:
+        # The "cmds" and "vcp" caps can be a mapping
         if key in ["cmds", "vcp"]:
             caps_dict[key] = _convert_to_dict(_extract_a_cap(caps_str, key))
         else:
@@ -625,6 +627,10 @@ def _parse_capabilities(caps_str: str) -> dict:
 
     # Parse the input sources into a text list for readability
     input_source_cap = vcp_codes.input_select.value
+
+    # Put this check here to appease the type checker
+    if isinstance(caps_dict["vcp"], str):
+        raise ValueError("VCP capabilities dictionary is the wrong type!")
     if input_source_cap in caps_dict["vcp"]:
         caps_dict["inputs"] = []
         input_val_list = list(caps_dict["vcp"][input_source_cap].keys())
diff --git a/monitorcontrol/vcp/vcp_abc.py b/monitorcontrol/vcp/vcp_abc.py
index 7b0a1c5..b50013c 100644
--- a/monitorcontrol/vcp/vcp_abc.py
+++ b/monitorcontrol/vcp/vcp_abc.py
@@ -21,9 +21,9 @@ class VCPPermissionError(VCPError):
     pass
 
 
-class VCP(abc.ABC):
+class VCP[T](abc.ABC):
     @abc.abstractmethod
-    def __enter__(self):
+    def __enter__(self) -> T:
         pass
 
     @abc.abstractmethod
@@ -64,3 +64,7 @@ def get_vcp_feature(self, code: int) -> Tuple[int, int]:
             VCPError: Failed to get VCP feature.
         """
         pass
+
+    @abc.abstractmethod
+    def get_vcp_capabilities(self) -> str:
+        pass
diff --git a/monitorcontrol/vcp/vcp_linux.py b/monitorcontrol/vcp/vcp_linux.py
index 983bd37..c90e979 100644
--- a/monitorcontrol/vcp/vcp_linux.py
+++ b/monitorcontrol/vcp/vcp_linux.py
@@ -55,7 +55,7 @@ def __init__(self, bus_number: int):
         """
         self.logger = logging.getLogger(__name__)
         self.bus_number = bus_number
-        self.fd: Optional[str] = None
+        self.fd: Optional[int] = None
         self.fp: str = f"/dev/i2c-{self.bus_number}"
         # time of last feature set call
         self.last_set: Optional[float] = None
@@ -64,7 +64,7 @@ def __enter__(self):
         def cleanup(fd: Optional[int]):
             if fd is not None:
                 try:
-                    os.close(self.fd)
+                    os.close(fd)
                 except OSError:
                     pass
 
@@ -90,7 +90,8 @@ def __exit__(
         exception_traceback: Optional[TracebackType],
     ) -> Optional[bool]:
         try:
-            os.close(self.fd)
+            if self.fd:
+                os.close(self.fd)
         except OSError as e:
             raise VCPIOError("unable to close descriptor") from e
         self.fd = None
@@ -359,11 +360,14 @@ def read_bytes(self, num_bytes: int) -> bytes:
             VCPIOError: unable to read data
         """
         try:
-            return os.read(self.fd, num_bytes)
+            if self.fd:
+                return os.read(self.fd, num_bytes)
+            else:
+                raise VCPIOError("unable read from I2C bus: no open file descriptor")
         except OSError as e:
             raise VCPIOError("unable to read from I2C bus") from e
 
-    def write_bytes(self, data: bytes):
+    def write_bytes(self, data: bytes | bytearray):
         """
         Writes bytes to the I2C bus.
 
@@ -374,12 +378,15 @@ def write_bytes(self, data: bytes):
             VCPIOError: unable to write data
         """
         try:
-            os.write(self.fd, data)
+            if self.fd:
+                os.write(self.fd, data)
+            else:
+                VCPIOError("unable write to I2C bus: no open file descriptor found")
         except OSError as e:
             raise VCPIOError("unable write to I2C bus") from e
 
 
-def get_vcps() -> List[LinuxVCP]:
+def get_vcps() -> List[VCP]:
     """
     Interrogates I2C buses to determine if they are DDC-CI capable.
 
diff --git a/monitorcontrol/vcp/vcp_windows.py b/monitorcontrol/vcp/vcp_windows.py
index c15abf1..d03f944 100644
--- a/monitorcontrol/vcp/vcp_windows.py
+++ b/monitorcontrol/vcp/vcp_windows.py
@@ -16,6 +16,14 @@
     WCHAR,
 )
 
+# Move some aliases here so we can have our type
+# ignoring in one place
+
+# pyrefly: ignore[missing-attribute]
+c_windll = ctypes.windll
+# pyrefly: ignore[missing-attribute]
+c_formaterror = ctypes.FormatError
+
 
 # structure type for a physical monitor
 class PhysicalMonitor(ctypes.Structure):
@@ -37,11 +45,12 @@ def __init__(self, handle: HANDLE, description: str):
             description: Text description of the physical monitor.
         """
         self.logger = logging.getLogger(__name__)
-        self.handle = handle
+        self.handle_p = handle
+        self.handle = int(handle)
         self.description = description
 
     def __del__(self):
-        WindowsVCP._destroy_physical_monitor(self.handle)
+        WindowsVCP._destroy_physical_monitor(self.handle_p)
 
     def __enter__(self):
         pass
@@ -70,10 +79,10 @@ def set_vcp_feature(self, code: int, value: int):
             extra=dict(code=code, value=value),
         )
         try:
-            if not ctypes.windll.dxva2.SetVCPFeature(
-                HANDLE(self.handle), BYTE(code), DWORD(value)
+            if not c_windll.dxva2.SetVCPFeature(
+                HANDLE(int(self.handle)), BYTE(code), DWORD(value)
             ):
-                raise VCPError("failed to set VCP feature: " + ctypes.FormatError())
+                raise VCPError("failed to set VCP feature: " + c_formaterror())
         except OSError as e:
             raise VCPError("failed to close handle") from e
 
@@ -97,14 +106,14 @@ def get_vcp_feature(self, code: int) -> Tuple[int, int]:
             extra=dict(code=code),
         )
         try:
-            if not ctypes.windll.dxva2.GetVCPFeatureAndVCPFeatureReply(
+            if not c_windll.dxva2.GetVCPFeatureAndVCPFeatureReply(
                 HANDLE(self.handle),
                 BYTE(code),
                 None,
                 ctypes.byref(feature_current),
                 ctypes.byref(feature_max),
             ):
-                raise VCPError("failed to get VCP feature: " + ctypes.FormatError())
+                raise VCPError("failed to get VCP feature: " + c_formaterror())
         except OSError as e:
             raise VCPError("failed to get VCP feature") from e
         self.logger.debug(
@@ -131,20 +140,16 @@ def get_vcp_capabilities(self):
         cap_length = DWORD()
         self.logger.debug("GetCapabilitiesStringLength")
         try:
-            if not ctypes.windll.dxva2.GetCapabilitiesStringLength(
+            if not c_windll.dxva2.GetCapabilitiesStringLength(
                 HANDLE(self.handle), ctypes.byref(cap_length)
             ):
-                raise VCPError(
-                    "failed to get VCP capabilities: " + ctypes.FormatError()
-                )
+                raise VCPError("failed to get VCP capabilities: " + c_formaterror())
             cap_string = (ctypes.c_char * cap_length.value)()
             self.logger.debug("CapabilitiesRequestAndCapabilitiesReply")
-            if not ctypes.windll.dxva2.CapabilitiesRequestAndCapabilitiesReply(
+            if not c_windll.dxva2.CapabilitiesRequestAndCapabilitiesReply(
                 HANDLE(self.handle), cap_string, cap_length
             ):
-                raise VCPError(
-                    "failed to get VCP capabilities: " + ctypes.FormatError()
-                )
+                raise VCPError("failed to get VCP capabilities: " + c_formaterror())
         except OSError as e:
             raise VCPError("failed to get VCP capabilities") from e
         return cap_string.value.decode("ascii")
@@ -167,7 +172,7 @@ def _get_hmonitors() -> List[HMONITOR]:
         """
         Calls the Windows `EnumDisplayMonitors` API in Python-friendly form.
         """
-        hmonitors = []  # type: List[HMONITOR]
+        hmonitors: List[HMONITOR] = []
         try:
 
             def _callback(hmonitor, hdc, lprect, lparam):
@@ -175,11 +180,12 @@ def _callback(hmonitor, hdc, lprect, lparam):
                 del hmonitor, hdc, lprect, lparam
                 return True  # continue enumeration
 
+            # pyrefly: ignore[missing-attribute]
             MONITORENUMPROC = ctypes.WINFUNCTYPE(  # noqa: N806
                 BOOL, HMONITOR, HDC, ctypes.POINTER(RECT), LPARAM
             )
             callback = MONITORENUMPROC(_callback)
-            if not ctypes.windll.user32.EnumDisplayMonitors(0, 0, callback, 0):
+            if not c_windll.user32.EnumDisplayMonitors(0, 0, callback, 0):
                 raise VCPError("Call to EnumDisplayMonitors failed")
         except OSError as e:
             raise VCPError("failed to enumerate VCPs") from e
@@ -194,12 +200,13 @@ def _physical_monitors_from_hmonitor(
         """
         num_physical = DWORD()
         try:
-            if not ctypes.windll.dxva2.GetNumberOfPhysicalMonitorsFromHMONITOR(
+            # pyrefly: ignore[missing-attribute]
+            if not c_windll.dxva2.GetNumberOfPhysicalMonitorsFromHMONITOR(
                 hmonitor, ctypes.byref(num_physical)
             ):
                 raise VCPError(
                     "Call to GetNumberOfPhysicalMonitorsFromHMONITOR failed: "
-                    + ctypes.FormatError()
+                    + c_formaterror()
                 )
         except OSError as e:
             raise VCPError(
@@ -208,17 +215,16 @@ def _physical_monitors_from_hmonitor(
 
         physical_monitors = (PhysicalMonitor * num_physical.value)()
         try:
-            if not ctypes.windll.dxva2.GetPhysicalMonitorsFromHMONITOR(
+            if not c_windll.dxva2.GetPhysicalMonitorsFromHMONITOR(
                 hmonitor, num_physical.value, physical_monitors
             ):
                 raise VCPError(
-                    "Call to GetPhysicalMonitorsFromHMONITOR failed: "
-                    + ctypes.FormatError()
+                    "Call to GetPhysicalMonitorsFromHMONITOR failed: " + c_formaterror()
                 )
         except OSError as e:
             raise VCPError("failed to open physical monitor handle") from e
         return (
-            [physical_monitor.handle, physical_monitor.description]
+            (physical_monitor.handle, physical_monitor.description)
             for physical_monitor in physical_monitors
         )
 
@@ -228,9 +234,9 @@ def _destroy_physical_monitor(handle: HANDLE) -> None:
         Calls the Windows `DestroyPhysicalMonitor` API in Python-friendly form.
         """
         try:
-            if not ctypes.windll.dxva2.DestroyPhysicalMonitor(handle):
+            if not c_windll.dxva2.DestroyPhysicalMonitor(handle):
                 raise VCPError(
-                    "Call to DestroyPhysicalMonitor failed: " + ctypes.FormatError()
+                    "Call to DestroyPhysicalMonitor failed: " + c_formaterror()
                 )
         except OSError as e:
             raise VCPError("failed to close handle") from e
diff --git a/pyproject.toml b/pyproject.toml
index bcd4295..ef9d2ea 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,9 +10,17 @@ dependencies = [
     "pyudev>=0.23.3 ; sys_platform != 'win32'",
 ]
 
+[tool.pyrefly]
+project-includes = ["**/*"]
+project-excludes = [
+    "**/__pycache__",
+    "**/*venv/**/*",
+]
+
 [dependency-groups]
 dev = [
     "coveralls>=4.0.1",
+    "pyrefly>=v0.37.0",
     "pytest>=8.3.4",
     "pytest-cov>=6.0.0",
     "ruff>=0.11.11",
diff --git a/tests/test_cli.py b/tests/test_cli.py
index e804690..eca2db7 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -1,4 +1,5 @@
 from .test_monitorcontrol import UnitTestVCP
+import monitorcontrol.__main__
 from monitorcontrol import Monitor
 from monitorcontrol.__main__ import main, count_to_level
 from unittest import mock
diff --git a/tests/test_monitorcontrol.py b/tests/test_monitorcontrol.py
index 7255ea2..13e8a14 100644
--- a/tests/test_monitorcontrol.py
+++ b/tests/test_monitorcontrol.py
@@ -52,7 +52,8 @@ def __exit__(
 
 
 def test_context_manager_assert():
-    m = Monitor(None)
+    vcps = get_test_vcps()
+    m = Monitor(vcps[0])
     with pytest.raises(AssertionError):
         m.get_power_mode()
 
@@ -65,7 +66,7 @@ def test_get_monitors():
     get_monitors()
 
 
-def get_test_vcps() -> List[Type[vcp.VCP]]:
+def get_test_vcps() -> List[vcp.VCP]:
     if USE_ATTACHED_MONITORS:
         return get_vcps()
     else:
@@ -222,6 +223,7 @@ def test_input_source_issue_59(monitor: Monitor):
 
 def test_input_source_type_error(monitor: Monitor):
     with pytest.raises(TypeError):
+        # pyrefly: ignore[bad-argument-type]
         monitor.set_input_source([])
 
 
diff --git a/tests/test_windows_vcp.py b/tests/test_windows_vcp.py
index 3bddc92..b6833e2 100644
--- a/tests/test_windows_vcp.py
+++ b/tests/test_windows_vcp.py
@@ -1,6 +1,9 @@
+import sys
 import pytest
 from unittest.mock import patch
 
+if not sys.platform.startswith("win"):
+    pytest.skip("skipping windows-only tests", allow_module_level=True)
 
 from monitorcontrol.vcp.vcp_windows import WindowsVCP