diff --git a/dtk/__init__.py b/dtk/__init__.py
index fbc18ba..78c9094 100644
--- a/dtk/__init__.py
+++ b/dtk/__init__.py
@@ -2,4 +2,5 @@
 # encoding: utf-8
 
 from . import argv
+from . import aux
 from . import cfg
diff --git a/dtk/argv.py b/dtk/argv.py
index 6b3cf30..1b9ee5f 100644
--- a/dtk/argv.py
+++ b/dtk/argv.py
@@ -3,12 +3,14 @@
 
 import sys
 
+from . import aux
+
 class Action:
 	"""
 	A callable with signature:
 	
-	p_args is a list of (name, type) tuples
-	kv_args is a dict with {name: (type, default value), ...}
+	p_args is a list of (name, type, desc) tuples
+	kv_args is a dict with {name: (type, default value, desc), ...}
 	"""
 	
 	p_args = []
@@ -94,10 +96,10 @@ class Invocation:
 			return
 		
 		# pre-populate args
-		for name, T in self.action.p_args:
+		for name, *_ in self.action.p_args:
 			self.args[name] = None
 		
-		for name, (T, default) in self.action.kv_args.items():
+		for name, (T, default, _) in self.action.kv_args.items():
 			self.args[name] = T(default)
 		
 		# process positional (mandatory) args
@@ -107,7 +109,7 @@ class Invocation:
 		if not len(raw_p_args) == count_p_args:
 			raise IncompleteInvocation
 		
-		for raw, (name, T) in zip(raw_p_args, self.action.p_args):
+		for raw, (name, T, _) in zip(raw_p_args, self.action.p_args):
 			try:
 				self.args[name] = T(raw)
 			except:
@@ -131,35 +133,44 @@ class Invocation:
 	
 	def execute(self):
 		self.action(self.cmd, **self.args)
-
-# ~ $ nicectl customer create NAME [--note=xxx]
-
-# ~ $ nicectl user create CUSTOMER LOGIN
-# ~ generated password is printed
-
-# ~ $ nicectl unit list
-
-# ~ $ nicectl unit create CUSTOMER NAME MODEL [--serial=XXX] [--note=xxx]
-
-# ~ routing = {
-	# ~ "customer": {
-		# ~ "create": customer_create,
-		# ~ "list": customer_list
-	# ~ },
-	# ~ "user": {
-		# ~ "create": user_create,
-		# ~ "list": user_list
-	# ~ },
-	# ~ "unit": {
-		# ~ "create": unit_create,
-		# ~ "list": unit_list
-	# ~ }
-# ~ }
+	
+	def help(self, stream=sys.stdout):
+		"""
+		Prints auto-generated usage information.
+		"""
+		
+		print("Usage:")
+		
+		for cmd, act in aux.flatten_dict(self.routing):
+			synopsis = ["$", sys.argv[0], cmd]
+			args = []
+			
+			for name, T, desc in act.p_args:
+				synopsis.append(name)
+				args.append("* %s (%s) = %s" %(name, T.__name__, desc))
+			
+			if act.kv_args:
+				synopsis.append("[")
+				
+				for name, (T, default, desc) in act.kv_args.items():
+					synopsis.append("%s=%s" %(name, default or "…"))
+					args.append("+ %s (%s) = %s" %(name, T.__name__, desc))
+				
+				synopsis.append("]")
+			
+			print("  " + " ".join(synopsis))
+			for arg in args:
+				print("    " + arg)
+			
+			print()
+			print("      " + act.__doc__.strip())
+			
+			print()
 
 if __name__ == "__main__":
 	class TestActionHello(Action):
-		p_args = [("NAME", str), ("AGE", int)]
-		kv_args = {"speed": (float, 75)}
+		p_args = [("NAME", str, "description"), ("AGE", int, "another short piece of wisdom")]
+		kv_args = {"speed": (float, 75, "more stuff")}
 		
 		def __call__(self, cmd, NAME, AGE, speed):
 			print("Hello %s, age %d." %(NAME, AGE))
diff --git a/dtk/aux.py b/dtk/aux.py
new file mode 100644
index 0000000..687fc10
--- /dev/null
+++ b/dtk/aux.py
@@ -0,0 +1,15 @@
+#! /usr/bin/env python3
+# encoding: utf-8
+
+def flatten_dict(root, glue=" ", prefix=[]):
+	lines = []
+	
+	for k, v in root.items():
+		new_prefix = prefix + [k]
+		
+		if type(v) == dict:
+			lines.extend(flatten_dict(v, glue, new_prefix))
+		else:
+			lines.append((glue.join(new_prefix), v))
+	
+	return lines