diff --git a/cli.py b/cli.py
index 417ee77..e8f3c4f 100644
--- a/cli.py
+++ b/cli.py
@@ -39,7 +39,7 @@ def build(files, lib):
 
         with open(f"{name}.yaml", "w") as template:
             click.echo(f'{head} Saving to "{name}.yaml"')
-            template.write(ct.yaml)
+            template.write(ct.yaml())
 
 
 cli.add_command(build)
diff --git a/poetry.lock b/poetry.lock
index 9ad1a3e..87162a0 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -15,6 +15,14 @@ optional = false
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 version = "1.3.0"
 
+[[package]]
+category = "main"
+description = "Simple decorator to set attributes of target function or class in a DRY way."
+name = "attr"
+optional = false
+python-versions = "*"
+version = "0.3.1"
+
 [[package]]
 category = "dev"
 description = "Classes Without Boilerplate"
@@ -312,12 +320,13 @@ version = "0.6.0"
 more-itertools = "*"
 
 [metadata]
-content-hash = "8b98f0ec71c743eaa4b4e20ea47a27623933499bc148691cb9e6873769973491"
+content-hash = "34aba17e7f55024ab4816c63d2f35b6e40e62692876d018dae01f0e782d6e9d4"
 python-versions = "^3.7"
 
 [metadata.hashes]
 appdirs = ["9e5896d1372858f8dd3344faf4e5014d21849c756c8d5701f78f8a103b372d92", "d8b24664561d0d34ddfaec54636d502d7cea6e29c3eaf68f3df6180863e2166e"]
 atomicwrites = ["03472c30eb2c5d1ba9227e4c2ca66ab8287fbfbbda3888aa93dc2e28fc6811b4", "75a9445bac02d8d058d5e1fe689654ba5a6556a1dfd8ce6ec55a0ed79866cfa6"]
+attr = ["0b1aaddb85bd9e9c4bd75092f4440d6616ff40b0df0437f00771871670f7c9fd", "9091548058d17f132596e61fa7518e504f76b9a4c61ca7d86e1f96dbf7d4775d"]
 attrs = ["08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c", "f7b7ce16570fe9965acd6d30101a28f62fb4a7f9e926b3bbc9b61f8b04247e72"]
 black = ["09a9dcb7c46ed496a9850b76e4e825d6049ecd38b611f1224857a79bd985a8cf", "68950ffd4d9169716bcb8719a56c07a2f4485354fec061cdd5910aa07369731c"]
 click = ["2335065e6395b9e67ca716de5f7526736bfa6ceead690adf616d925bdc622b13", "5b94b49521f6456670fdb30cd82a4eca9412788a93fa6dd6df72c94d5a8ff2d7"]
diff --git a/policytool/models.py b/policytool/models.py
index 4fe30ea..c021cfe 100644
--- a/policytool/models.py
+++ b/policytool/models.py
@@ -1,5 +1,6 @@
 from typing import List
 
+import attr
 import yaml
 
 
@@ -9,15 +10,27 @@ def str_presenter(dumper, data):
     return dumper.represent_scalar("tag:yaml.org,2002:str", data)
 
 
+@attr.s(auto_attribs=True)
 class ConstraintTemplate(object):
-    def __init__(self, kind: str, rego: str, libs: List[str] = []):
-        self.name = kind.lower()
-        self.kind = kind
-        self.list_kind = f"{kind}List"
-        self.plural = self.name
-        self.singular = self.name.rstrip("s")
-        self.rego = rego
-        self.libs = libs
+    kind: str
+    rego: str
+    libs: List[str] = attr.Factory(list)
+
+    @property
+    def name(self):
+        return self.kind.lower()
+
+    @property
+    def plural(self):
+        return self.name
+
+    @property
+    def singular(self):
+        return self.name.rstrip("s")
+
+    @property
+    def list_kind(self):
+        return f"{self.kind}List"
 
     @property
     def _template(self):
@@ -45,7 +58,6 @@ def _template(self):
             temp["spec"]["targets"][0]["libs"] = self.libs
         return temp
 
-    @property
     def yaml(self):
         yaml.add_representer(str, str_presenter)
         return yaml.dump(self._template)
diff --git a/policytool/test_models.py b/policytool/test_models.py
index 78608e6..f695ee1 100644
--- a/policytool/test_models.py
+++ b/policytool/test_models.py
@@ -44,7 +44,7 @@ def test_default_libs(self, template):
 
     def test_yaml(self, template):
         assert (
-            template.yaml
+            template.yaml()
             == """apiVersion: templates.gatekeeper.sh/v1beta1
 kind: ConstraintTemplate
 metadata:
diff --git a/pyproject.toml b/pyproject.toml
index 4237d7e..9dc3e7e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,13 +5,14 @@ license = "Apache-2.0"
 description = "A set of utilities and classes for working with Open Policy Agent based tools, including Gatekeeper and Conftest"
 authors = ["Gareth Rushgrove <gareth@morethanseven.net>"]
 readme = "README.md"
-repository = "https://github.com/garethr/policytool
+repository = "https://github.com/garethr/policytool"
 
 [tool.poetry.dependencies]
 python = "^3.7"
 PyYAML = "^5.1"
 click = "^7.0"
 colorama = "^0.4.1"
+attr = "^0.3.1"
 
 [tool.poetry.scripts]
 policytool = "cli:cli"