diff --git a/README.md b/README.md
index 2548c09..b8b1b87 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,8 @@ If bundler is not being used to manage dependencies, install the gem by executin
 
 ```sh
 Usage:    flatito PATH [options]
-Example:  flatito . -k hello
+Example:  flatito . -k "search string" -e "json,yaml"
+Example:  cat file.yaml | flatito -k "search string"
 
     -h, --help                       Prints this help
     -V, --version                    Show version
diff --git a/exe/flatito b/exe/flatito
index b077efc..cfa9d3d 100755
--- a/exe/flatito
+++ b/exe/flatito
@@ -6,14 +6,15 @@ require "flatito"
 require "optparse"
 
 # If no arguments are given, print help
-ARGV << "-h" if ARGV.empty?
+stdin = $stdin.read unless $stdin.tty?
+ARGV << "-h" if ARGV.empty? && !stdin
 
 options = {}
 OptionParser.new do |opts|
   opts.banner = <<~HEREDOC
     Usage:    flatito PATH [options]
-    Example:  flatito . -k hello
-
+    Example:  flatito . -k "search string" -e "json,yaml"
+    Example:  cat file.yaml | flatito -k "search string"
   HEREDOC
 
   opts.on("-h", "--help", "Prints this help") do
@@ -43,8 +44,10 @@ OptionParser.new do |opts|
   end
 end.parse!
 
-begin
+Flatito::Config.prepare_with_options(options)
+
+if stdin
+  Flatito.flat_content(stdin, options)
+else
   Flatito.search(ARGV, options)
-rescue Interrupt
-  warn "\nInterrupted"
 end
diff --git a/lib/flatito.rb b/lib/flatito.rb
index a618b2c..df3c213 100644
--- a/lib/flatito.rb
+++ b/lib/flatito.rb
@@ -9,9 +9,20 @@
 require_relative "flatito/yaml_with_line_number"
 require_relative "flatito/renderer"
 require_relative "flatito/regex_from_search"
+require_relative "flatito/print_items"
+require_relative "flatito/config"
 
 module Flatito
-  def self.search(paths, options)
-    Finder.new(paths, options).call
+  class << self
+    def search(paths, options = {})
+      Finder.new(paths, options).call
+    rescue Interrupt
+      warn "\nInterrupted"
+    end
+
+    def flat_content(content, options = {})
+      items = FlattenYaml.items_from_content(content)
+      PrintItems.new(options[:search]).print(items)
+    end
   end
 end
diff --git a/lib/flatito/config.rb b/lib/flatito/config.rb
new file mode 100644
index 0000000..fe51d2d
--- /dev/null
+++ b/lib/flatito/config.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module Flatito
+  module Config
+    @stdout = $stdout
+    @stderr = $stderr
+    @stdin  = $stdin
+
+    class << self
+      attr_accessor :renderer, :stdout, :stder, :stdin
+
+      def prepare_with_options(options)
+        self.renderer = Renderer.build(options)
+      end
+    end
+  end
+end
diff --git a/lib/flatito/finder.rb b/lib/flatito/finder.rb
index 34ea41a..2593928 100644
--- a/lib/flatito/finder.rb
+++ b/lib/flatito/finder.rb
@@ -8,14 +8,14 @@ class Finder
 
     DEFAULT_EXTENSIONS = %w[json yml yaml].freeze
 
-    attr_reader :paths, :search, :extensions, :options, :renderer
+    attr_reader :paths, :search, :extensions, :options, :print_items
 
     def initialize(paths, options = {})
       @paths = paths
       @search = options[:search]
       @extensions = prepare_extensions(options[:extensions] || DEFAULT_EXTENSIONS)
       @options = options
-      @renderer = Renderer.build(options)
+      @print_items = PrintItems.new(search)
     end
 
     def call
@@ -36,14 +36,13 @@ def call
 
     private
 
-    def flat_and_filter(pathname)
-      items = FlattenYaml.new(pathname).items
-      items = filter_by_search(items) if search
-
-      return unless items.any?
+    def renderer
+      Config.renderer
+    end
 
-      renderer.print_pathname(pathname)
-      renderer.print_items(items)
+    def flat_and_filter(pathname)
+      items = FlattenYaml.items_from_path(pathname)
+      print_items.print(items, pathname)
     end
 
     def prepare_extensions(extensions)
@@ -51,11 +50,5 @@ def prepare_extensions(extensions)
         ext.start_with?(".") ? ext : ".#{ext}"
       end
     end
-
-    def filter_by_search(items)
-      items.select do |item|
-        regex.match?(item.key)
-      end
-    end
   end
 end
diff --git a/lib/flatito/flatten_yaml.rb b/lib/flatito/flatten_yaml.rb
index 3fdb5c1..bea8838 100644
--- a/lib/flatito/flatten_yaml.rb
+++ b/lib/flatito/flatten_yaml.rb
@@ -1,9 +1,26 @@
 # frozen_string_literal: true
 
+require_relative "utils"
 module Flatito
   class FlattenYaml
+    include Utils
+
     Item = Struct.new(:key, :value, :line, keyword_init: true)
-    def initialize(pathname)
+    class << self
+      def items_from_path(pathname)
+        content = File.read(pathname)
+        new(content, pathname: pathname).items
+      end
+
+      def items_from_content(content)
+        new(content).items
+      end
+    end
+
+    attr_reader :content, :pathname
+
+    def initialize(content, pathname: nil)
+      @content = content
       @pathname = pathname
     end
 
@@ -23,28 +40,20 @@ def flatten_hash(hash, prefix = nil)
           end
         end
       end
-    rescue StandardError => e
-      warn "Error parsing #{@pathname}, #{e.message}"
     end
 
     def with_line_numbers
       handler = YAMLWithLineNumber::TreeBuilder.new
       handler.parser = Psych::Parser.new(handler)
 
-      handler.parser.parse(File.read(@pathname))
+      handler.parser.parse(content)
       YAMLWithLineNumber::VisitorsToRuby.create.accept(handler.root)
     rescue Psych::SyntaxError
-      warn "Invalid YAML #{@pathname}"
-
+      warn "Invalid format #{pathname}"
       []
-    rescue StandardError => e
-      warn "Error parsing #{@pathname}, #{e.message}"
-
+    rescue StandardError
+      warn "Error parsing #{pathname}"
       []
     end
-
-    def truncate(string, max = 50)
-      string.length > max ? "#{string[0...max]}..." : string
-    end
   end
 end
diff --git a/lib/flatito/print_items.rb b/lib/flatito/print_items.rb
new file mode 100644
index 0000000..8558a02
--- /dev/null
+++ b/lib/flatito/print_items.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+module Flatito
+  class PrintItems
+    include RegexFromSearch
+    attr_reader :search
+
+    def initialize(search)
+      @search = search
+    end
+
+    def print(items, pathname = nil)
+      items = filter_by_search(items) if search
+      return unless items.any?
+
+      renderer.print_pathname(pathname) if pathname
+      renderer.print_items(items)
+    end
+
+    def filter_by_search(items)
+      items.select do |item|
+        regex.match?(item.key)
+      end
+    end
+
+    def renderer
+      Config.renderer
+    end
+  end
+end
diff --git a/lib/flatito/renderer.rb b/lib/flatito/renderer.rb
index a5d7d7b..0949bd0 100644
--- a/lib/flatito/renderer.rb
+++ b/lib/flatito/renderer.rb
@@ -2,25 +2,23 @@
 
 require "io/console"
 require_relative "regex_from_search"
+require_relative "utils"
 
 module Flatito
   class Renderer
-    include RegexFromSearch
-
     def self.build(options)
-      if tty?
+      if Config.stdout.tty?
         Renderer::TTY.new(options)
       else
         Renderer::Plain.new(options)
       end
     end
-
-    def self.tty?
-      $stdout.tty?
-    end
   end
 
   class Base
+    include Utils
+    include RegexFromSearch
+
     attr_reader :search, :no_color
 
     def initialize(options)
@@ -33,7 +31,7 @@ def print_file_progress(pathname); end
     def ending; end
 
     def print_pathname(pathname)
-      puts colorize(pathname.to_s, :light_blue)
+      stdout.puts colorize(pathname.to_s, :light_blue)
     end
 
     def print_items(items)
@@ -42,8 +40,8 @@ def print_items(items)
       items.each do |item|
         print_item(item, line_number_padding)
       end
-      puts
-      flush
+      stdout.puts
+      stdout.flush
     end
 
     def print_item(item, line_number_padding)
@@ -54,19 +52,11 @@ def print_item(item, line_number_padding)
                 ""
               end
 
-      puts "#{line_number} #{matched_string(item.key)} #{value}"
+      stdout.puts "#{line_number} #{matched_string(item.key)} #{value}"
     end
 
     private
 
-    def flush
-      stdout.flush
-    end
-
-    def regex
-      @regex ||= Regexp.new(search)
-    end
-
     def matched_string(string)
       return string if search.nil? || no_color?
 
@@ -80,12 +70,8 @@ def no_color?
       ENV["TERM"] == "dumb" || ENV["NO_COLOR"] == "true" || no_color == true
     end
 
-    def truncate(string, max = 50)
-      string.length > max ? "#{string[0...max]}..." : string
-    end
-
     def stdout
-      $stdout
+      Config.stdout
     end
 
     def colorize(string, color)
@@ -95,7 +81,7 @@ def colorize(string, color)
 
   class Renderer::Plain < Base
     def ending
-      puts
+      stdout.puts
     end
   end
 
@@ -128,19 +114,19 @@ def print_pathname(pathname)
     def ending
       clear_line
       show_cursor
-      puts
+      stdout.puts
     end
 
     def hide_cursor
-      print HIDE_CURSOR
+      stdout.print HIDE_CURSOR
     end
 
     def show_cursor
-      print SHOW_CURSOR
+      stdout.print SHOW_CURSOR
     end
 
     def clear_line
-      print CLEAR_LINE
+      stdout.print CLEAR_LINE
     end
 
     private
diff --git a/lib/flatito/utils.rb b/lib/flatito/utils.rb
new file mode 100644
index 0000000..733023a
--- /dev/null
+++ b/lib/flatito/utils.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module Flatito
+  module Utils
+    def truncate(string, max = 50)
+      string.length > max ? "#{string[0...max]}..." : string
+    end
+  end
+end
diff --git a/lib/flatito/yaml_with_line_number.rb b/lib/flatito/yaml_with_line_number.rb
index e70fbd3..2c0e90b 100644
--- a/lib/flatito/yaml_with_line_number.rb
+++ b/lib/flatito/yaml_with_line_number.rb
@@ -30,8 +30,6 @@ def respond_to_missing?(*)
 
     class ClassLoader < Psych::ClassLoader
       def find(klassname)
-        @cache[klassname] ||= resolve(klassname)
-      rescue ArgumentError
         Whatever.new(klassname)
       end
     end
diff --git a/test/fixtures/with_ruby_objects.yml b/test/fixtures/with_ruby_objects.yml
index b52c464..d667799 100644
--- a/test/fixtures/with_ruby_objects.yml
+++ b/test/fixtures/with_ruby_objects.yml
@@ -3,6 +3,6 @@ two: !ruby/object:OpenStruct
   table:
     one: One
     two: Two
-three: !ruby/object:UnknowClass
+three: !ruby/object:UnknownClass
   one: One
   two: Two
diff --git a/test/flatito/config_test.rb b/test/flatito/config_test.rb
new file mode 100644
index 0000000..40c1340
--- /dev/null
+++ b/test/flatito/config_test.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class Flatito::ConfigTest < Minitest::Test
+  class DummyTTY < StringIO
+    def tty?
+      true
+    end
+  end
+
+  class DummyNotTTY < StringIO
+    def tty?
+      false
+    end
+  end
+
+  test "when stdout is tty set renderer as tty" do
+    Flatito::Config.stdout = DummyTTY.new
+    Flatito::Config.prepare_with_options({})
+
+    assert_kind_of Flatito::Renderer::TTY, Flatito::Config.renderer
+  end
+
+  test "when stdout is not tty set renderer as plain" do
+    Flatito::Config.stdout = DummyNotTTY.new
+    Flatito::Config.prepare_with_options({})
+
+    assert_kind_of Flatito::Renderer::Plain, Flatito::Config.renderer
+  end
+end
diff --git a/test/flatito/flatten_yaml_test.rb b/test/flatito/flatten_yaml_test.rb
index 8be2c11..405caab 100644
--- a/test/flatito/flatten_yaml_test.rb
+++ b/test/flatito/flatten_yaml_test.rb
@@ -4,7 +4,7 @@
 
 class Flatito::FlattenYamlTest < Minitest::Test
   test "a json" do
-    items = Flatito::FlattenYaml.new("test/fixtures/a.json").items
+    items = Flatito::FlattenYaml.items_from_path("test/fixtures/a.json")
 
     assert_equal 5, items.size
     assert_equal "one", items[0].key
@@ -13,7 +13,7 @@ class Flatito::FlattenYamlTest < Minitest::Test
   end
 
   test "no nested" do
-    items = Flatito::FlattenYaml.new("test/fixtures/no_nested.yml").items
+    items = Flatito::FlattenYaml.items_from_path("test/fixtures/no_nested.yml")
 
     assert_equal 3, items.size
     assert_equal "one", items[0].key
@@ -22,7 +22,7 @@ class Flatito::FlattenYamlTest < Minitest::Test
   end
 
   test "nested" do
-    items = Flatito::FlattenYaml.new("test/fixtures/nested.yml").items
+    items = Flatito::FlattenYaml.items_from_path("test/fixtures/nested.yml")
 
     assert_equal 3, items.size
     assert_equal "nested1.one", items[0].key
@@ -39,7 +39,7 @@ class Flatito::FlattenYamlTest < Minitest::Test
   end
 
   test "with merging hashes" do
-    items = Flatito::FlattenYaml.new("test/fixtures/merge.yml").items
+    items = Flatito::FlattenYaml.items_from_path("test/fixtures/merge.yml")
 
     assert_equal 3, items.size
 
@@ -57,7 +57,7 @@ class Flatito::FlattenYamlTest < Minitest::Test
   end
 
   test "multiline values" do
-    items = Flatito::FlattenYaml.new("test/fixtures/multiline.yml").items
+    items = Flatito::FlattenYaml.items_from_path("test/fixtures/multiline.yml")
 
     assert_equal "en.long_message", items[0].key
     assert_equal 2, items[0].line
@@ -67,12 +67,26 @@ class Flatito::FlattenYamlTest < Minitest::Test
   end
 
   test "with ruby objects" do
-    items = Flatito::FlattenYaml.new("test/fixtures/with_ruby_objects.yml").items
+    items = Flatito::FlattenYaml.items_from_path("test/fixtures/with_ruby_objects.yml")
 
     assert_equal 3, items.size
 
     assert_equal "two", items[1].key
     assert_equal "[object: OpenStruct]", items[1].value
     assert_equal 2, items[1].line
+
+    assert_equal "three", items[2].key
+    assert_equal "[object: UnknownClass]", items[2].value
+    assert_equal 6, items[2].line
+  end
+
+  test "items from content with duplicated keys" do
+    content = File.read("test/fixtures/no_nested.yml")
+    items = Flatito::FlattenYaml.items_from_content(content)
+
+    assert_equal 3, items.size
+    assert_equal "one", items[0].key
+    assert_equal "One", items[0].value
+    assert_equal 1, items[0].line
   end
 end