diff --git a/src/Serializing/Format.hs b/src/Serializing/Format.hs
index 6c1700598..da9b82677 100644
--- a/src/Serializing/Format.hs
+++ b/src/Serializing/Format.hs
@@ -1 +1,11 @@
-module Serializing.Format where
+{-# LANGUAGE GADTs #-}
+module Serializing.Format
+( Format(..)
+, Builder
+) where
+
+import Algebra.Graph.Class
+import Data.ByteString.Builder
+
+data Format input where
+  DOT :: (Ord vertex, ToGraph graph, ToVertex graph ~ vertex) => Style vertex Builder -> Format graph