Try defining functions as suggested by @grst

src/rich_click/__init__.py

@@ -9,7 +9,26 @@
 __version__ = "0.4.0.dev0"
 
 from click import *
-from .rich_click import rich_format_help
+from .rich_click import RichGroup
+from .rich_click import RichCommand
 from .rich_click import rich_format_error
-from .rich_click import Group
-from .rich_click import Command
+
+## TODO: Replace with inheritance / custom function model as below
+# Monkey patch click error formatting function
+ClickException.show = rich_format_error
+UsageError.show = rich_format_error
+
+
+def group(*args, cls=RichGroup, **kwargs):
+    from click import group as click_group
+
+    return click_group(*args, cls=cls, **kwargs)
+
+
+def command(*args, cls=RichCommand, **kwargs):
+    from click import command as click_command
+
+    return click_command(*args, cls=cls, **kwargs)
+
+    ## TODO: This works for simple top-level commands,
+    # but not commands nested within a group

src/rich_click/rich_click.py

@@ -362,11 +362,21 @@ def rich_format_error(self):
     )
 
 
-class Group(click.Group):
+class RichGroup(click.Group):
     def format_help(self, ctx, formatter):
         rich_format_help(self, ctx, formatter)
 
 
-class Command(click.Command):
+class RichCommand(click.Command):
     def format_help(self, ctx, formatter):
         rich_format_help(self, ctx, formatter)
+
+
+class RichClickException(click.ClickException):
+    def show(self, file):
+        rich_format_error(self, file)
+
+
+class RichUsageError(click.UsageError):
+    def show(self, file):
+        rich_format_error(self, file)