diff --git a/.github/workflows/documentation.yml b/.github/workflows/documentation.yml
new file mode 100644
index 0000000..b7409d4
--- /dev/null
+++ b/.github/workflows/documentation.yml
@@ -0,0 +1,29 @@
+name: website
+
+on:
+  push:
+    branches: [ master ]
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Crystal
+        uses: crystal-lang/install-crystal@v1
+        with:
+          crystal: nightly
+      - name: Check out repository code
+        uses: actions/checkout@v2
+      - name: Install dependencies
+        run: shards install
+      - name: Generate documentation
+        run: crystal docs
+      -
+        name: Deploy to GitHub Pages
+        if: success()
+        uses: crazy-max/ghaction-github-pages@v2
+        with:
+          target_branch: gh-pages
+          build_dir: docs
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
diff --git a/src/mechanize/cookie.cr b/src/mechanize/cookie.cr
index 0b3e44d..3c8c6aa 100644
--- a/src/mechanize/cookie.cr
+++ b/src/mechanize/cookie.cr
@@ -1,5 +1,6 @@
-# TODO: want to add methods with safe way like Ruby's refinement.
+# TODO: want to property's without open HTTP::Cookie class.
 
+# This class represents http cookie.
 # open HTTP::Cookie class to add origin property.
 # origin property represents the origin of the resource.
 # if cookie's domain attribute isn't designated,
diff --git a/src/mechanize/errors/element_not_found_error.cr b/src/mechanize/errors/element_not_found_error.cr
index fd35a4a..7456b35 100644
--- a/src/mechanize/errors/element_not_found_error.cr
+++ b/src/mechanize/errors/element_not_found_error.cr
@@ -1,5 +1,6 @@
 require "./base_error"
 
+# This error means matched elements are not found by *_with method.
 class Mechanize::ElementNotFoundError < Mechanize::Error
   getter element : Symbol
   getter conditions : String
diff --git a/src/mechanize/file.cr b/src/mechanize/file.cr
index 02539b4..9ec0b40 100644
--- a/src/mechanize/file.cr
+++ b/src/mechanize/file.cr
@@ -1,9 +1,15 @@
 require "http/client"
 
 class Mechanize
-  class File
-    # property :body, :filename
-    property :body, :code, uri, :response
+  abstract class File
+    # property :filename
+
+    # returns http response body
+    getter body : String
+    # returns http status code
+    getter code : Int32
+    # returns page uri
+    getter uri : URI
 
     def initialize(uri : URI, response : ::HTTP::Client::Response, body : String, code : Int32)
       @uri = uri
diff --git a/src/mechanize/form.cr b/src/mechanize/form.cr
index bbd3e8f..f3a8606 100644
--- a/src/mechanize/form.cr
+++ b/src/mechanize/form.cr
@@ -8,20 +8,31 @@ require "./form/button"
 require "./form/select_list"
 require "./utils/element_matcher"
 
+# This class represents the form tag of html.
 class Mechanize::Form
   include Mechanize::ElementMatcher
 
   getter node : Node | Lexbor::Node
-  getter fields : Array(Mechanize::FormContent::Field)
-  getter checkboxes : Array(Mechanize::FormContent::CheckBox)
-  getter radiobuttons : Array(Mechanize::FormContent::RadioButton)
-  getter selectboxes : Array(Mechanize::FormContent::MultiSelectList)
-  getter buttons : Array(Mechanize::FormContent::Button)
+  # returns hoge array of `Mechanize::FormContent::Field` in the form.
+  getter fields : Array(FormContent::Field)
+  # returns an array of input tags whose type is checkbox in the form.
+  getter checkboxes : Array(FormContent::CheckBox)
+  # returns an array of input tags whose type is radio in the form.
+  getter radiobuttons : Array(FormContent::RadioButton)
+  # returns an array of input tags whose type is select in the form.
+  getter selectboxes : Array(FormContent::MultiSelectList)
+  # returns an array of button tags and input tag whose type is button,submit,reset,image.
+  getter buttons : Array(FormContent::Button)
+  # returns form's 'enctype' attribute.
   getter enctype : String
+  # returns form's 'method' attribute.
   getter method : String
+  # returns form's 'name' attribute.
   getter name : String
-  getter page : Mechanize::Page?
+  # return form's 'action' attribute.
   property action : String
+  # returns the page which includes the form.
+  getter page : Mechanize::Page?
 
   def initialize(node : Node | Lexbor::Node, page : Mechanize::Page? = nil)
     @enctype = node.fetch("enctype", "application/x-www-form-urlencoded")
@@ -57,7 +68,7 @@ class Mechanize::Form
   elements_with "checkbox", "checkboxes"
   elements_with "button"
 
-  # Returns all fields of type Textarea
+  # Returns all fields of <input type="textarea">
   def textareas
     fields.select { |f| f.class == FormContent::Textarea }.map &.as(FormContent::Textarea)
   end
diff --git a/src/mechanize/form/button.cr b/src/mechanize/form/button.cr
index 8a610bf..4a55eda 100644
--- a/src/mechanize/form/button.cr
+++ b/src/mechanize/form/button.cr
@@ -1,3 +1,5 @@
+# This class represents button related html element.
+# <button>, and <input> whose type is button, reset, image, submit.
 class Mechanize::FormContent::Button < Mechanize::FormContent::Field
   getter form_node : Node | Lexbor::Node
 
diff --git a/src/mechanize/form/check_box.cr b/src/mechanize/form/check_box.cr
index e383441..b239cbf 100644
--- a/src/mechanize/form/check_box.cr
+++ b/src/mechanize/form/check_box.cr
@@ -1,4 +1,6 @@
+# This class represents <input type="checkbox">
 class Mechanize::FormContent::CheckBox < Mechanize::FormContent::RadioButton
+  # set checkbox checked
   def check
     @checked = true
   end
diff --git a/src/mechanize/form/field.cr b/src/mechanize/form/field.cr
index 4eb7c23..f98ffee 100644
--- a/src/mechanize/form/field.cr
+++ b/src/mechanize/form/field.cr
@@ -1,7 +1,13 @@
+# This class represents <input> elements in the form.
 class Mechanize::FormContent::Field
+  # returns field's 'value' attribute
   property value : String?
+  # returns field's 'name' attribute
   getter name : String
+  # returns field's 'type' attribute
   getter type : String
+  # returns field's 'value' attribute.
+  # value property is changeable, but this property stores raw value.
   getter raw_value : String?
   getter node : Node | Lexbor::Node
 
@@ -17,12 +23,12 @@ class Mechanize::FormContent::Field
     [@name, @value || ""]
   end
 
-  # returns DOM 'id' value
+  # returns field's 'id' value
   def dom_id
     node.fetch("id", "")
   end
 
-  # returns DOM 'class' value
+  # returns field's 'class' value
   def dom_class
     node.fetch("class", "")
   end
diff --git a/src/mechanize/form/hidden.cr b/src/mechanize/form/hidden.cr
index ca409dd..59557f6 100644
--- a/src/mechanize/form/hidden.cr
+++ b/src/mechanize/form/hidden.cr
@@ -1,2 +1,3 @@
+# This class represents <input type="hidden">
 class Mechanize::FormContent::Hidden < Mechanize::FormContent::Field
 end
diff --git a/src/mechanize/form/image_button.cr b/src/mechanize/form/image_button.cr
index 1cd1d68..583f39d 100644
--- a/src/mechanize/form/image_button.cr
+++ b/src/mechanize/form/image_button.cr
@@ -1,2 +1,3 @@
+# This class represents <input type="image">
 class Mechanize::FormContent::ImageButton < Mechanize::FormContent::Button
 end
diff --git a/src/mechanize/form/multi_select_list.cr b/src/mechanize/form/multi_select_list.cr
index f55f518..a960c72 100644
--- a/src/mechanize/form/multi_select_list.cr
+++ b/src/mechanize/form/multi_select_list.cr
@@ -1,5 +1,6 @@
 require "./option"
 
+# This class represents <select multiple>
 class Mechanize::FormContent::MultiSelectList
   getter node : Lexbor::Node
   getter name : String
@@ -18,32 +19,37 @@ class Mechanize::FormContent::MultiSelectList
     }
   end
 
+  # set all options unchecked
   def select_none
     @values = Array(String).new
     options.each &.unselect
   end
 
+  # set all options checked
   def select_all
     @values = Array(String).new
     options.each &.select
   end
 
+  # returns all checked options
   def selected_options
     options.select &.selected?
   end
 
+  # add new values to options
   def values=(new_values)
     select_none
     new_values.each do |value|
       option = options.find { |o| o.value == value }
       if option.nil?
-        @value.push(value)
+        @values.push(value)
       else
         option.select
       end
     end
   end
 
+  # return all option's values.
   def values
     @values + selected_options.map &.value
   end
diff --git a/src/mechanize/form/option.cr b/src/mechanize/form/option.cr
index 2079b22..ad5d4e5 100644
--- a/src/mechanize/form/option.cr
+++ b/src/mechanize/form/option.cr
@@ -30,6 +30,7 @@ class Mechanize::FormContent::Option
     @selected = !@selected
   end
 
+  # returns option checked or not
   def selected?
     @selected
   end
diff --git a/src/mechanize/form/radio_button.cr b/src/mechanize/form/radio_button.cr
index 1987d95..b37aab5 100644
--- a/src/mechanize/form/radio_button.cr
+++ b/src/mechanize/form/radio_button.cr
@@ -1,3 +1,4 @@
+# This class represents <input type="radio">
 class Mechanize::FormContent::RadioButton < Mechanize::FormContent::Field
   property :checked, :form
 
@@ -7,19 +8,23 @@ class Mechanize::FormContent::RadioButton < Mechanize::FormContent::Field
     super(node)
   end
 
+  # set radiobutton checked
   def check
     uncheck_peers
     @checked = true
   end
 
+  # set radiobutton checked
   def uncheck
     @checked = false
   end
 
+  # change radiobutton state checked or unchecked
   def click
     checked ? uncheck : check
   end
 
+  # returns radiobutton checked or not
   def checked?
     checked
   end
diff --git a/src/mechanize/form/reset_button.cr b/src/mechanize/form/reset_button.cr
index baa3970..a5385e7 100644
--- a/src/mechanize/form/reset_button.cr
+++ b/src/mechanize/form/reset_button.cr
@@ -1,2 +1,3 @@
+# This class represents <input type="reset">
 class Mechanize::FormContent::ResetButton < Mechanize::FormContent::Button
 end
diff --git a/src/mechanize/form/select_list.cr b/src/mechanize/form/select_list.cr
index b3acde2..4670e08 100644
--- a/src/mechanize/form/select_list.cr
+++ b/src/mechanize/form/select_list.cr
@@ -1,5 +1,6 @@
 require "./multi_select_list"
 
+# This class represents <select> which is not multiple
 class Mechanize::FormContent::SelectList < Mechanize::FormContent::MultiSelectList
   def initialize(node)
     super node
diff --git a/src/mechanize/form/submit_button.cr b/src/mechanize/form/submit_button.cr
index 691da00..90aa146 100644
--- a/src/mechanize/form/submit_button.cr
+++ b/src/mechanize/form/submit_button.cr
@@ -1,2 +1,3 @@
+# This class represents <input type="submit">
 class Mechanize::FormContent::SubmitButton < Mechanize::FormContent::Button
 end
diff --git a/src/mechanize/form/text.cr b/src/mechanize/form/text.cr
index 894dafd..e39fd47 100644
--- a/src/mechanize/form/text.cr
+++ b/src/mechanize/form/text.cr
@@ -1,2 +1,3 @@
+# This class represents <input type="text">
 class Mechanize::FormContent::Text < Mechanize::FormContent::Field
 end
diff --git a/src/mechanize/form/textarea.cr b/src/mechanize/form/textarea.cr
index b7c825a..39a4094 100644
--- a/src/mechanize/form/textarea.cr
+++ b/src/mechanize/form/textarea.cr
@@ -1,2 +1,3 @@
+# This class represents <input type="textarea">
 class Mechanize::FormContent::Textarea < Mechanize::FormContent::Field
 end
diff --git a/src/mechanize/history.cr b/src/mechanize/history.cr
index b5d4fd2..5448079 100644
--- a/src/mechanize/history.cr
+++ b/src/mechanize/history.cr
@@ -1,7 +1,11 @@
 require "./page"
 
+# This class represents the history of http response you sent.
+# If you send a request, mechanize saves the history.
 class Mechanize
   class History
+    # max page size history can save. default is 100.
+    # as same as `agent.max_history`.
     property max_size : Int32
     property array : Array(Mechanize::Page)
 
@@ -12,6 +16,7 @@ class Mechanize
       @array = array
     end
 
+    # add page to history.
     def push(page, uri = nil)
       @array.push(page)
       while size > @max_size
@@ -20,6 +25,7 @@ class Mechanize
       self
     end
 
+    # take the last page out from history.
     def pop
       if size == 0
         # TODO: raise error
diff --git a/src/mechanize/http/agent.cr b/src/mechanize/http/agent.cr
index f546ff9..86f9236 100644
--- a/src/mechanize/http/agent.cr
+++ b/src/mechanize/http/agent.cr
@@ -6,12 +6,13 @@ require "../history"
 class Mechanize
   module HTTP
     class Agent
-      property :request_headers, :context
+      property request_headers : ::HTTP::Headers
+      property context : Mechanize?
       property history : Mechanize::History
       property user_agent : String
       property request_cookies : ::HTTP::Cookies
 
-      def initialize(@context : Mechanize | Nil = nil)
+      def initialize(@context : Mechanize? = nil)
         @history = Mechanize::History.new
         @request_headers = ::HTTP::Headers.new
         @context = context
@@ -19,6 +20,9 @@ class Mechanize
         @user_agent = ""
       end
 
+      # send http request and return page.
+      # This method is called from Mechanize#get, #post and other methods.
+      # There's no need to call this method directly.
       def fetch(uri, method = :get, headers = ::HTTP::Headers.new, params = Hash(String, String).new,
                 referer = (current_page unless history.empty?))
         uri = resolve_url(uri, referer)
@@ -51,7 +55,8 @@ class Mechanize
         fetch(uri)
       end
 
-      def http_request(uri, method, params)
+      # send http request
+      private def http_request(uri, method, params) : ::HTTP::Client::Response?
         case uri.scheme.not_nil!.downcase
         when "http", "https"
           case method
@@ -63,20 +68,34 @@ class Mechanize
         end
       end
 
-      def current_page
+      # returns the page now mechanize visiting.
+      # ```
+      # agent.current_page
+      # ```
+      def current_page : Mechanize::Page
         @history.last
       end
 
-      def back
+      # returns the page mechanize previous visited.
+      # ```
+      # agent.back
+      # ```
+      def back : Mechanize::Page
         @history.pop
       end
 
       # Get maximum number of items allowed in the history.  The default setting is 100 pages.
-      def max_history
+      # ```
+      # agent.max_history # => 100
+      # ```
+      def max_history : Int32
         @history.max_size
       end
 
       # Set maximum number of items allowed in the history.
+      # ```
+      # agent.max_history = 1000
+      # ```
       def max_history=(length)
         @history.max_size = length
       end
diff --git a/src/mechanize/page.cr b/src/mechanize/page.cr
index 9bd1f2a..ff952be 100644
--- a/src/mechanize/page.cr
+++ b/src/mechanize/page.cr
@@ -2,13 +2,14 @@ require "./file"
 require "./utils/element_matcher"
 require "./page/link"
 
-# This class represents the page of response.
-# If you send request, it returns the instance of Page.
-# You can get status code, title, and page body, and search html node using css selector.
-
+# This class represents the result of http response.
+# If you send a request, it returns the instance of `Mechanize::Page`.
+# You can get status code, title, and page body, and search html node using css selector from page instance.
 class Mechanize
   class Page < Mechanize::File
     include Mechanize::ElementMatcher
+
+    # look at lexbor document.(https://github.com/kostya/lexbor#readme)
     delegate :css, to: parser
 
     property mech : Mechanize
@@ -25,6 +26,9 @@ class Mechanize
     end
 
     # return page title.
+    # ```
+    # page.title # => String
+    # ```
     def title : String
       title_node = css("title")
       if title_node.empty?
@@ -35,19 +39,25 @@ class Mechanize
     end
 
     # return all forms(`Mechanize::Form`) in the page.
+    # ```
+    # page.forms # => Array(Mechanize::Form)
+    # ```
     def forms : Array(Mechanize::Form)
       forms = css("form").map do |html_form|
-        form = Mechanize::Form.new(html_form, self)
+        form = Form.new(html_form, self)
         form.action ||= @uri.to_s
         form
       end.to_a
     end
 
-    # return all links(`Mechanize::PageContent::Link) in the page.
+    # return all links(`Mechanize::PageContent::Link`) in the page.
+    # ```
+    # page.links # => Array(Mechanize::PageContent::Link)
+    # ```
     def links : Array(Mechanize::PageContent::Link)
       links = %w{a area}.map do |tag|
         css(tag).map do |node|
-          Mechanize::PageContent::Link.new(node, @mech, self)
+          PageContent::Link.new(node, @mech, self)
         end
       end.flatten
     end
diff --git a/src/mechanize/page/link.cr b/src/mechanize/page/link.cr
index 1ecab2e..2267f64 100644
--- a/src/mechanize/page/link.cr
+++ b/src/mechanize/page/link.cr
@@ -1,3 +1,5 @@
+# This class represents link element like <a> and <area>.
+# The instance of this class is clickable.
 class Mechanize::PageContent::Link
   getter node : Lexbor::Node
   getter page : Mechanize::Page
diff --git a/src/mechanize/utils/element_matcher.cr b/src/mechanize/utils/element_matcher.cr
index 33f3e71..a653125 100644
--- a/src/mechanize/utils/element_matcher.cr
+++ b/src/mechanize/utils/element_matcher.cr
@@ -1,55 +1,73 @@
 class Mechanize
+  # This module is for macros making *_with methods.
+  # These methods are useful for searching elements by its' attribute.
   module ElementMatcher
     macro elements_with(singular, plural = "")
-    {% plural = "#{singular.id}s" if plural.empty? %}
-    # search {{ singular.id }} which matches condition.
-    #
-    # Examples
-    # ```
-    # # if you specify String like "foo", it searches form which name is "foo".
-    # # like {<form name="foo"></form>}
-    # page.form_with("foo")
-    #
-    # # you can specify tag's attribute and its' value by NamedTuple or Hash(String, String).
-    # ex) <form class="foo"></form>
-    # page.form_with("class" => "foo")
-    # page.form_with(class: "foo")
-    # ```
-    def {{plural.id}}_with(criteria : String | NamedTuple | Hash(String,String))
-      {{plural.id}}_with(criteria){}
-    end
+      {% plural = "#{singular.id}s" if plural.empty? %}
+      # search {{ plural.id }} which match condition.
+      # 
+      # Examples
+      # ```
+      # # if you specify String like "foo", it searches {{ singular.id }} which name is "foo".
+      {% if ["form", "button"].includes?("#{singular.id}") %}
+        # # like <{{ singular.id }} name="foo"></{{ singular.id }}>
+      {% elsif "#{singular.id}" == "field" %}
+      # # like <input name="foo"></input>
+      {% elsif "#{singular.id}" == "radiobutton" %}
+      # # like <input type="radio" name="foo"></input>
+      {% else %}
+      # # like <input type="{{ singular.id }}" name="foo"></input>
+      {% end %}
+      # page.{{ plural.id }}_with("foo")
+      # # you can also specify tag's attribute and its' value by NamedTuple or Hash(String, String).
+      {% if ["form", "button"].includes?("#{singular.id}") %}
+      # # ex) <{{ singular.id }} class="foo"></{{ singular.id }}>
+      {% elsif "#{singular.id}" == "field" %}
+      # # ex) <input class="foo"></input>
+      {% elsif "#{singular.id}" == "radiobutton" %}
+      # # ex) <input type="radio" class="foo"></input>
+      {% else %}
+      # # ex) <input type="{{ singular.id }}" class="foo"></input>
+      {% end %}
+      # page.{{ plural.id }}_with("class" => "foo")
+      # page.{{ plural.id }}_with(class: "foo")
+      # ```
+      def {{plural.id}}_with(criteria : String | NamedTuple | Hash(String,String))
+        {{plural.id}}_with(criteria){}
+      end
 
-    def {{plural.id}}_with(criteria, &block)
-      if criteria.is_a?(NamedTuple)
-        criteria = criteria.to_h
-      end
-      if criteria.is_a?(String)
-        criteria = {"name" => criteria}
-      else
-        criteria = criteria.each_with_object(Hash(String,String).new) do |(k, v), h|
-          k = k.to_s
-          h[k] = v
+      def {{plural.id}}_with(criteria, &block)
+        if criteria.is_a?(NamedTuple)
+          criteria = criteria.to_h
         end
-      end
-      f = {{plural.id}}.select do |elm|
-        criteria.all? do |k,v|
-          if k == "text"
-            v == elm.node.inner_text
-          else
-            v == elm.node.fetch(k,"")
+        if criteria.is_a?(String)
+          criteria = {"name" => criteria}
+        else
+          criteria = criteria.each_with_object(Hash(String,String).new) do |(k, v), h|
+            k = k.to_s
+            h[k] = v
           end
         end
+        f = {{plural.id}}.select do |elm|
+          criteria.all? do |k,v|
+            if k == "text"
+              v == elm.node.inner_text
+            else
+              v == elm.node.fetch(k,"")
+            end
+          end
+        end
+        yield f
+        f
       end
-      yield f
-      f
-    end
 
-    def {{singular.id}}_with(criteria)
-      f = {{plural.id}}_with(criteria)
-      # TODO: Write correct error message.
-      raise Mechanize::ElementNotFoundError.new(:{{singular.id}}, "") if f.empty?
-      f.first
+      # returns first element of `#{{ plural.id }}_with`
+      def {{singular.id}}_with(criteria)
+        f = {{plural.id}}_with(criteria)
+        # TODO: Write correct error message.
+        raise Mechanize::ElementNotFoundError.new(:{{singular.id}}, "") if f.empty?
+        f.first
+      end
     end
   end
-  end
 end