diff --git a/README.md b/README.md
index 1f05283..df0b6d7 100644
--- a/README.md
+++ b/README.md
@@ -6,18 +6,15 @@ TODO: Write a description here
 
 ```bash
 brew tap amberframework/micrate
-brew install micrate crystal
+brew install micrate
+
+shards install
 ```
 
 TODO: Write installation instructions here
 
 ## Usage
 
-```bash
-crystal build url-shortener.cr --release --progress
-ENV=production ./url-shortener
-```
-
 TODO: Write usage instructions here
 
 ## Development
@@ -27,6 +24,13 @@ DATABASE_URL=sqlite3://./sqlite/data.db micrate up
 crystal run url-shortener.cr
 ```
 
+## Build
+
+```bash
+crystal build url-shortener.cr --release --progress
+ENV=production ./url-shortener
+```
+
 ## Contributing
 
 1. Fork it (<https://github.com/your-github-user/url-shortener/fork>)
diff --git a/app/config/kemal.cr b/app/config/kemal.cr
index 3c49d66..8b2cf3c 100644
--- a/app/config/kemal.cr
+++ b/app/config/kemal.cr
@@ -1,5 +1,5 @@
 require "kemal"
 
 Kemal.config.env = ENV["ENV"]? || "development"
-Kemal.config.port = ENV["PORT"]?.try(&.to_i) || 3000
+Kemal.config.port = ENV["PORT"]?.try(&.to_i) || 4000
 Kemal.config.host_binding = ENV["HOST"]? || "0.0.0.0"
diff --git a/app/controllers/link.cr b/app/controllers/link.cr
index efd62b0..a20eda5 100644
--- a/app/controllers/link.cr
+++ b/app/controllers/link.cr
@@ -10,10 +10,10 @@ module App::Controllers::Link
     def call(env)
       json_params = env.params.json.to_h
       url = json_params.has_key?("url") ? json_params["url"] : nil
-      raise App::BadRequestException.new(env) if !url #TODO: return url "required field" error message
+      raise App::BadRequestException.new(env, {"url" => "Required field"}) if !url
 
       link = Link.new
-      link.id = UUID.v4().to_s
+      link.id = UUID.v4.to_s
       link.url = url.to_s
       link.slug = Random::Secure.urlsafe_base64(4)
 
@@ -21,10 +21,10 @@ module App::Controllers::Link
 
       if !changeset.valid?
         errors = {"errors" => map_changeset_errors(changeset.errors)}
-        raise App::UnprocessableEntityException.new(env, errors.to_json)
+        raise App::UnprocessableEntityException.new(env, errors)
       end
 
-      response = {"data" => App::Serializers::Link.new(link) }
+      response = {"data" => App::Serializers::Link.new(link)}
       response.to_json
     end
   end
@@ -44,7 +44,7 @@ module App::Controllers::Link
 
         changeset = Database.update(link)
         if changeset.errors.any?
-          Log.error { "Increase click counter failed: #{changeset.errors}"}
+          Log.error { "Increase click counter failed: #{changeset.errors}" }
         end
       end
 
@@ -62,10 +62,10 @@ module App::Controllers::Link
       link = Database.get(Link, id)
       raise App::NotFoundException.new(env) if !link
 
-      response = {"data" => App::Serializers::Link.new(link) }
+      response = {"data" => App::Serializers::Link.new(link)}
       response.to_json
     end
   end
 
-  #TODO: update, delete
+  # TODO: update, delete
 end
diff --git a/app/lib/errors.cr b/app/lib/errors.cr
index 954c97a..fd077b4 100644
--- a/app/lib/errors.cr
+++ b/app/lib/errors.cr
@@ -2,8 +2,9 @@ require "kemal"
 
 module App
   class BadRequestException < Kemal::Exceptions::CustomException
-    def initialize(context)
+    def initialize(context, message = Hash(String, String))
       context.response.status_code = 400
+      context.response.print({ "error" => message }.to_json)
       super(context)
     end
   end
@@ -16,11 +17,10 @@ module App
   end
 
   class UnprocessableEntityException < Kemal::Exceptions::CustomException
-    def initialize(context, @content = "")
+    def initialize(context, message = Hash(String, String))
       context.response.status_code = 422
+      context.response.print({ "error" => message }.to_json)
       super(context)
     end
-
-    getter :content
   end
 end
diff --git a/app/serializers/link.cr b/app/serializers/link.cr
index b739be2..d735b13 100644
--- a/app/serializers/link.cr
+++ b/app/serializers/link.cr
@@ -11,8 +11,8 @@ module App::Serializers
       builder.object do
         builder.field("id", @link.id)
         builder.field("link", "#{ENV["APP_URL"]}/#{@link.slug}")
-        builder.field("clicks", @link.click_counter)
         builder.field("origin", @link.url)
+        builder.field("clicks", @link.click_counter)
       end
     end
   end
diff --git a/shard.lock b/shard.lock
index f249219..2125b7f 100644
--- a/shard.lock
+++ b/shard.lock
@@ -24,10 +24,6 @@ shards:
     git: https://github.com/kemalcr/kemal.git
     version: 1.5.0
 
-  micrate:
-    git: https://github.com/amberframework/micrate.git
-    version: 0.3.3
-
   radix:
     git: https://github.com/luislavena/radix.git
     version: 0.4.1
diff --git a/url-shortener.cr b/url-shortener.cr
index eaf1604..b4c888f 100644
--- a/url-shortener.cr
+++ b/url-shortener.cr
@@ -7,9 +7,8 @@ require "./app/serializers/*"
 
 require "./app/routes"
 
-error 500 { |env| {"status" => 500, "error" => "Internal Server Error"}.to_json }
-error 401 { |env| {"status" => 401, "error" => "Unauthorized"}.to_json }
-error 403 { |env| {"status" => 403, "error" => "Forbidden"}.to_json }
-error 404 { |env| {"status" => 404, "error" => "Not Found"}.to_json }
+error 500 { |env| {"error" => "Internal Server Error"}.to_json }
+error 401 { |env| {"error" => "Unauthorized"}.to_json }
+error 403 { |env| {"error" => "Forbidden"}.to_json }
 
 Kemal.run