diff --git a/heat/engine/function.py b/heat/engine/function.py
index 2f48ff2e82..f5a091ab83 100644
--- a/heat/engine/function.py
+++ b/heat/engine/function.py
@@ -36,6 +36,15 @@ class Function(object):
         self.fn_name = fn_name
         self.args = args
 
+    def validate(self):
+        """
+        Validate arguments without resolving the function.
+
+        Function subclasses must override this method to validate their
+        args.
+        """
+        validate(self.args)
+
     @abc.abstractmethod
     def result(self):
         """
@@ -110,3 +119,15 @@ def resolve(snippet):
         return [resolve(v) for v in snippet]
 
     return snippet
+
+
+def validate(snippet):
+    if isinstance(snippet, Function):
+        snippet.validate()
+    elif isinstance(snippet, collections.Mapping):
+        for v in snippet.values():
+            validate(v)
+    elif (not isinstance(snippet, basestring) and
+          isinstance(snippet, collections.Iterable)):
+        for v in snippet:
+            validate(v)
diff --git a/heat/tests/test_function.py b/heat/tests/test_function.py
index e0d2241b3c..885846dce3 100644
--- a/heat/tests/test_function.py
+++ b/heat/tests/test_function.py
@@ -19,6 +19,10 @@ from heat.engine import function
 
 
 class TestFunction(function.Function):
+    def validate(self):
+        if len(self.args) < 2:
+            raise Exception(_('Need more arguments'))
+
     def result(self):
         return 'wibble'
 
@@ -80,3 +84,42 @@ class ResolveTest(HeatTestCase):
         self.assertEqual(['foo', {'bar': ['baz', {'blarg': 'wibble'}]}],
                          result)
         self.assertIsNot(result, snippet)
+
+
+class ValidateTest(HeatTestCase):
+    def setUp(self):
+        super(ValidateTest, self).setUp()
+        self.func = TestFunction(None, 'foo', ['bar', 'baz'])
+
+    def test_validate_func(self):
+        self.assertIsNone(function.validate(self.func))
+        self.func = TestFunction(None, 'foo', ['bar'])
+        ex = self.assertRaises(Exception, function.validate, self.func)
+        self.assertEqual('Need more arguments', str(ex))
+
+    def test_validate_dict(self):
+        snippet = {'foo': 'bar', 'blarg': self.func}
+        function.validate(snippet)
+
+        self.func = TestFunction(None, 'foo', ['bar'])
+        snippet = {'foo': 'bar', 'blarg': self.func}
+        ex = self.assertRaises(Exception, function.validate, snippet)
+        self.assertEqual('Need more arguments', str(ex))
+
+    def test_validate_list(self):
+        snippet = ['foo', 'bar', 'baz', 'blarg', self.func]
+        function.validate(snippet)
+
+        self.func = TestFunction(None, 'foo', ['bar'])
+        snippet = {'foo': 'bar', 'blarg': self.func}
+        ex = self.assertRaises(Exception, function.validate, snippet)
+        self.assertEqual('Need more arguments', str(ex))
+
+    def test_validate_all(self):
+        snippet = ['foo', {'bar': ['baz', {'blarg': self.func}]}]
+        function.validate(snippet)
+
+        self.func = TestFunction(None, 'foo', ['bar'])
+        snippet = {'foo': 'bar', 'blarg': self.func}
+        ex = self.assertRaises(Exception, function.validate, snippet)
+        self.assertEqual('Need more arguments', str(ex))