diff --git a/src/clj/grub/sync.clj b/src/clj/grub/sync.clj
new file mode 100644
index 0000000..e4cc300
--- /dev/null
+++ b/src/clj/grub/sync.clj
@@ -0,0 +1,21 @@
+(ns grub.sync
+  (:require [clojure.data :as data]
+            [clojure.pprint :as pprint :refer [pprint]]
+            [clojure.set :as set]))
+
+(defn deleted [a b]
+  (set/difference (into #{} (keys a)) (into #{} (keys b))))
+
+(defn updated [a b]
+  (second (data/diff a b)))
+
+(defn diff [a b]
+  {:deleted (deleted a b)
+   :updated (changed a b)})
+
+(defn diff-states [prev next]
+  (->> prev
+       (keys)
+       (map (fn [k] [k (diff (k prev) (k next))]))
+       (into {})))
+
diff --git a/src/test/grub/test/unit/sync.clj b/src/test/grub/test/unit/sync.clj
new file mode 100644
index 0000000..c552fd3
--- /dev/null
+++ b/src/test/grub/test/unit/sync.clj
@@ -0,0 +1,76 @@
+(ns grub.test.unit.sync
+  (:require [grub.sync :as sync]
+            [clojure.test :refer :all]))
+
+(def server-state
+  {:grubs 
+   {"grub-same" {:id "grub-same", 
+                 :completed false, 
+                 :grub "3 garlic cloves"}
+    "grub-completed" {:id "grub-completed", 
+                      :completed false, 
+                      :grub "2 tomatoes"}
+    "grub-updated" {:id "grub-updated", 
+                    :completed false, 
+                    :grub "BBQ sauce"}
+    "grub-deleted" {:id "grub-deleted"
+                    :completed true
+                    :grub "diapers"}}
+   :recipes 
+   {"recipe-same" {:id "recipe-same"
+                   :grubs "3 T. butter\n1 yellow onion\n1 1/2 dl red pepper\n1 dl apple\n3 garlic cloves\n1 t. curry\n3 dl water\n2-2 1/2 T. wheat flour\n1 kasvisliemikuutio\n200 g blue cheese\n2 dl apple juice\n2 dl milk\n1 t. basil\n1 package take-and-bake french bread"
+                   :name "Blue Cheese Soup"}
+    "recipe-updated" {:id "recipe-updated"
+                      :grubs "450 g lean stew beef (lapa/naudan etuselkä), cut into 1-inch cubes\n2 T. vegetable oil\n5 dl water\n2 lihaliemikuutios\n350 ml burgundy (or another red wine)\n1 garlic clove\n1 bay leaf (laakerinlehti)\n1/2 t. basil\n3 carrots\n1 yellow onion\n4 potatoes\n1 cup celery\n2 tablespoons of cornstarch (maissijauho/maizena)"
+                      :name "Beef Stew"}
+    "recipe-deleted" {:id "recipe-deleted"
+                      :grubs "8 slices rye bread\n400 g chicken breast\nBBQ sauce\nketchup\nmustard\nbutter\n1 package rocket\n4 tomatoes\n2 red onions\n1 bottle Coca Cola"
+                      :name "Chickenburgers"}}})
+
+(def client-state
+  {:grubs 
+   {"grub-same" {:id "grub-same", 
+                 :completed false, 
+                 :grub "3 garlic cloves"}
+    "grub-completed" {:id "grub-completed", 
+                      :completed true, 
+                      :grub "2 tomatoes"}
+    "grub-updated" {:id "grub-updated", 
+                    :completed false, 
+                    :grub "Ketchup"}
+    "grub-added" {:id "grub-added"
+                  :completed false
+                  :grub "Toothpaste"}}
+   :recipes 
+   {"recipe-same" {:id "recipe-same"
+                   :grubs "3 T. butter\n1 yellow onion\n1 1/2 dl red pepper\n1 dl apple\n3 garlic cloves\n1 t. curry\n3 dl water\n2-2 1/2 T. wheat flour\n1 kasvisliemikuutio\n200 g blue cheese\n2 dl apple juice\n2 dl milk\n1 t. basil\n1 package take-and-bake french bread"
+                   :name "Blue Cheese Soup"}
+    "recipe-updated" {:id "recipe-updated"
+                      :grubs "300 g lean stew beef (lapa/naudan etuselkä), cut into 1-inch cubes\n2 T. vegetable oil\n5 dl water\n2 lihaliemikuutios\n400 ml burgundy (or another red wine)\n1 garlic clove\n1 bay leaf (laakerinlehti)\n1/2 t. basil\n2 carrots\n1 yellow onion\n4 potatoes\n1 cup celery\n2 tablespoons of cornstarch (maissijauho/maizena)"
+                      :name "Beef Stew"}
+    "recipe-added" {:id "recipe-added"
+                    :grubs "400 g ground beef\nhamburger buns\n2 red onions\n4 tomatoes\ncheddar cheese\nketchup\nmustard\npickles\nfresh basil\n1 bottle Coca Cola"
+                    :name "Burgers"}}})
+
+(def expected-diff
+  {:recipes
+   {:deleted #{"recipe-deleted"},
+    :updated
+    {"recipe-added"
+     {:name "Burgers",
+      :id "recipe-added",
+      :grubs
+      "400 g ground beef\nhamburger buns\n2 red onions\n4 tomatoes\ncheddar cheese\nketchup\nmustard\npickles\nfresh basil\n1 bottle Coca Cola"},
+     "recipe-updated"
+     {:grubs
+      "300 g lean stew beef (lapa/naudan etuselkä), cut into 1-inch cubes\n2 T. vegetable oil\n5 dl water\n2 lihaliemikuutios\n400 ml burgundy (or another red wine)\n1 garlic clove\n1 bay leaf (laakerinlehti)\n1/2 t. basil\n2 carrots\n1 yellow onion\n4 potatoes\n1 cup celery\n2 tablespoons of cornstarch (maissijauho/maizena)"}}},
+   :grubs
+   {:deleted #{"grub-deleted"},
+    :updated
+    {"grub-completed" {:completed true},
+     "grub-updated" {:grub "Ketchup"},
+     "grub-added"
+     {:completed false, :grub "Toothpaste", :id "grub-added"}}}})
+
+(deftest diffing
+  (is (= (sync/diff-states server-state client-state) expected-diff)))