diff --git a/backend/src/uxbox/api/pages.clj b/backend/src/uxbox/api/pages.clj
index 8a84591be..3094a1c8b 100644
--- a/backend/src/uxbox/api/pages.clj
+++ b/backend/src/uxbox/api/pages.clj
@@ -13,20 +13,41 @@
             [uxbox.util.spec :as us]
             [uxbox.util.uuid :as uuid]))
 
+;; --- Common Specs
+
+(s/def ::id ::us/uuid)
+(s/def ::name string?)
+(s/def ::project ::us/uuid)
+(s/def ::version (s/and integer? pos?))
+(s/def ::data any?)
+(s/def ::metadata any?)
+
+;; --- List Pages
+
+(s/def ::list-pages|query
+  (s/keys :req-un [::project]))
+
 (defn list-pages
-  {:parameters {:query {:project [st/required st/uuid-str]}}}
+  {:parameters {:query ::list-pages|query}
+   :validation :spec}
   [{:keys [user parameters]}]
   (let [project (get-in parameters [:query :project])
         message {:user user :project project :type :list-pages-by-project}]
     (-> (sv/query message)
         (p/then rsp/ok))))
 
+;; --- Create Page
+
+(s/def ::create-page|body
+  (s/keys :req-un [::data
+                   ::metadata
+                   ::project
+                   ::name]
+          :opt-un [::id]))
+
 (defn create-page
-  {:parameters {:body {:data [st/required]
-                       :metadata [st/required]
-                       :project [st/required st/uuid]
-                       :name [st/required st/string]
-                       :id [st/uuid]}}}
+  {:parameters {:body ::create-page|body}
+   :validation :spec}
   [{:keys [user parameters]}]
   (let [data (get parameters :body)
         message (assoc data :user user :type :create-page)]
@@ -35,14 +56,23 @@
                   (let [loc (str "/api/pages/" (:id result))]
                     (rsp/created loc result)))))))
 
+;; --- Update Page
+
+(s/def ::update-page|path
+  (s/keys :req-un [::id]))
+
+(s/def ::update-page|body
+  (s/keys :req-un [::data
+                   ::metadata
+                   ::project
+                   ::name
+                   ::version]
+          :opt-un [::id]))
+
 (defn update-page
-  {:parameters {:path {:id [st/required st/uuid-str]}
-                :body {:data [st/required]
-                       :metadata [st/required]
-                       :project [st/required st/uuid]
-                       :name [st/required st/string]
-                       :version [st/required st/integer]
-                       :id [st/uuid]}}}
+  {:parameters {:path ::update-page|path
+                :body ::update-page|body}
+   :validation :spec}
   [{:keys [user parameters]}]
   (let [id (get-in parameters [:path :id])
         data (get parameters :body)
@@ -50,12 +80,21 @@
     (->> (sv/novelty message)
          (p/map #(rsp/ok %)))))
 
+;; --- Update Page Metadata
+
+(s/def ::update-page-metadata|path
+  (s/keys :req-un [::id]))
+
+(s/def ::update-page-metadata|body
+  (s/keys :req-un [::id
+                   ::metadata
+                   ::project
+                   ::name]))
+
 (defn update-page-metadata
-  {:parameters {:path {:id [st/required st/uuid-str]}
-                :body {:id [st/required st/uuid]
-                       :metadata [st/required]
-                       :project [st/required st/uuid]
-                       :name [st/required st/string]}}}
+  {:parameters {:path ::update-page-metadata|path
+                :body ::update-page-metadata|body}
+   :validation :spec}
   [{:keys [user parameters]}]
   (let [id (get-in parameters [:path :id])
         data (get parameters :body)
@@ -63,20 +102,39 @@
     (->> (sv/novelty message)
          (p/map rsp/ok))))
 
+;; --- Delete Page
+
+(s/def ::delete-page|path
+  (s/keys :req-un [::id]))
+
 (defn delete-page
-  {:parameters {:path {:id [st/required st/uuid-str]}}}
+  {:parameters {:path ::delete-page|path}
+   :validation :spec}
   [{:keys [user parameters]}]
   (let [id (get-in parameters [:path :id])
         message {:id id :type :delete-page :user user}]
     (-> (sv/novelty message)
         (p/then (constantly (rsp/no-content))))))
 
+;; --- Retrieve Page History
+
+(s/def ::max ::us/integer)
+(s/def ::since ::us/integer)
+(s/def ::pinned ::us/boolean)
+
+(s/def ::retrieve-page-history|path
+  (s/keys :req-un [::id]))
+
+(s/def ::retrieve-page-history|query
+  (s/keys :req-un [::max
+                   ::since
+                   ::pinned]))
+
 (defn retrieve-page-history
   "Retrieve the page history"
-  {:parameters {:path {:id [st/required st/uuid-str]}
-                :query {:max [st/integer-str]
-                        :since [st/integer-str]
-                        :pinned [st/boolean-str]}}}
+  {:parameters {:path ::retrieve-page-history|path
+                :query ::retrieve-page-history|query}
+   :validation :spec}
   [{:keys [user parameters]}]
   (let [id (get-in parameters [:path :id])
         data (get parameters :query)
@@ -84,11 +142,21 @@
     (->> (sv/query message)
          (p/map rsp/ok))))
 
+;; --- Update page history
+
+(s/def ::hid ::us/uuid)
+(s/def ::label string?)
+
+(s/def ::update-page-history|path
+  (s/keys :req-un [::id ::hid]))
+
+(s/def ::update-page-history|body
+  (s/keys :req-un [::label ::pinned]))
+
 (defn update-page-history
-  {:parameters {:path {:id [st/required st/uuid-str]
-                       :hid [st/required st/uuid-str]}
-                :body {:label [st/required st/string]
-                       :pinned [st/required st/boolean]}}}
+  {:parameters {:path ::update-page-history|path
+                :body ::update-page-history|body}
+   :validation :spec}
   [{:keys [user parameters]}]
   (let [{:keys [id hid]} (get parameters :path)
         message (assoc (get parameters :body)
diff --git a/backend/src/uxbox/util/exceptions.clj b/backend/src/uxbox/util/exceptions.clj
index 6d22b9b36..70db97db5 100644
--- a/backend/src/uxbox/util/exceptions.clj
+++ b/backend/src/uxbox/util/exceptions.clj
@@ -5,16 +5,27 @@
 ;; Copyright (c) 2016 Andrey Antukh <niwi@niwi.nz>
 
 (ns uxbox.util.exceptions
-  "A helpers for work with exceptions.")
+  "A helpers for work with exceptions."
+  (:require [clojure.spec.alpha :as s]))
+
+(s/def ::type keyword?)
+(s/def ::code keyword?)
+(s/def ::mesage string?)
+(s/def ::hint string?)
+(s/def ::cause #(instance? Exception %))
+(s/def ::error-params
+  (s/keys :req-un [::type]
+          :opt-un [::code
+                   ::hint
+                   ::mesage
+                   ::cause]))
 
 (defn error
-  [& {:keys [type code message] :or {type :unexpected} :as payload}]
-  {:pre [(keyword? type) (keyword? code)]}
-  (let [message (if message
-                  (str message " / " (pr-str code) "")
-                  (pr-str code))
-        payload (assoc payload :type type)]
-    (ex-info message payload)))
+  [& {:keys [type code message hint cause] :as params}]
+  (s/assert ::error-params params)
+  (let [message (or message hint "")
+        payload (dissoc params :cause :message)]
+    (ex-info message payload cause)))
 
 (defmacro raise
   [& args]
diff --git a/backend/src/uxbox/util/spec.clj b/backend/src/uxbox/util/spec.clj
index bbfe81b19..fdf729369 100644
--- a/backend/src/uxbox/util/spec.clj
+++ b/backend/src/uxbox/util/spec.clj
@@ -25,11 +25,8 @@
   [spec data]
   (let [result (s/conform spec data)]
     (if (= result ::s/invalid)
-      (ex/raise :type :validation
-                :code ::invalid
-                :message (s/explain-str spec data)
-                :context (s/explain-data spec data))
-      result)))
+      [nil (s/explain-data spec data)]
+      [result nil])))
 
 (defn valid?
   [spec data]
@@ -41,7 +38,7 @@
 
 (defn email?
   [v]
-  (and string?
+  (and (string? v)
        (re-matches email-rx v)))
 
 (defn instant?
@@ -100,20 +97,21 @@
 
 ;; --- Default Specs
 
-(s/def ::integer-string (s/conformer integer-conformer str))
-(s/def ::uuid-string (s/conformer uuid-conformer str))
-(s/def ::boolean-string (s/conformer boolean-conformer boolean-unformer))
-(s/def ::positive-integer #(< 0 % Long/MAX_VALUE))
+(s/def ::integer (s/conformer integer-conformer str))
+(s/def ::uuid (s/conformer uuid-conformer str))
+(s/def ::boolean (s/conformer boolean-conformer boolean-unformer))
+(s/def ::positive pos?)
+(s/def ::negative neg?)
 (s/def ::uploaded-file any?)
-(s/def ::uuid uuid?)
 (s/def ::bytes bytes?)
 (s/def ::path path?)
+(s/def ::email email?)
 
-(s/def ::id ::uuid-string)
+;; TODO: deprecated
+(s/def ::id ::uuid)
 (s/def ::name string?)
 (s/def ::username string?)
 (s/def ::password string?)
 (s/def ::version integer?)
-(s/def ::email email?)
 (s/def ::token string?)
 
diff --git a/backend/src/uxbox/util/transit.clj b/backend/src/uxbox/util/transit.clj
index 649b99dd4..15c25c0b2 100644
--- a/backend/src/uxbox/util/transit.clj
+++ b/backend/src/uxbox/util/transit.clj
@@ -6,6 +6,7 @@
 
 (ns uxbox.util.transit
   (:require [cognitect.transit :as t]
+            [clojure.java.io :as io]
             [uxbox.util.time :as dt])
   (:import java.io.ByteArrayInputStream
            java.io.ByteArrayOutputStream
@@ -52,7 +53,7 @@
   ([data]
    (decode data nil))
   ([data opts]
-   (with-open [input (ByteArrayInputStream. data)]
+   (with-open [input (io/input-stream data)]
      (read! (reader input opts)))))
 
 (defn encode