diff --git a/config/dev.exs b/config/dev.exs
index 82fae0c..3d7ed8f 100644
--- a/config/dev.exs
+++ b/config/dev.exs
@@ -2,3 +2,4 @@ import Config
 
 config(:onigumo, :http_client, HTTPoison)
 config(:onigumo, :downloader, Onigumo.Downloader)
+config(:onigumo, :parser, Onigumo.Parser)
diff --git a/lib/cli.ex b/lib/cli.ex
index 6a76a11..4ace1e4 100644
--- a/lib/cli.ex
+++ b/lib/cli.ex
@@ -1,6 +1,7 @@
 defmodule Onigumo.CLI do
   @components %{
-    :downloader => Application.compile_env(:onigumo, :downloader)
+    :downloader => Application.compile_env(:onigumo, :downloader),
+    :parser => Application.compile_env(:onigumo, :parser)
   }
 
   def main(argv) do
diff --git a/lib/onigumo/parser.ex b/lib/onigumo/parser.ex
new file mode 100644
index 0000000..9691253
--- /dev/null
+++ b/lib/onigumo/parser.ex
@@ -0,0 +1,26 @@
+defmodule Onigumo.Parser do
+  @moduledoc """
+  Web scraper
+  """
+  @behaviour Onigumo.Component
+
+  @impl Onigumo.Component
+  def main(root_path) do
+    root_path
+    |> list_downloaded()
+    |> Enum.map(&IO.puts(&1))
+
+    :ok
+  end
+
+  def list_downloaded(path) do
+    path
+    |> File.ls!()
+    |> Enum.filter(&is_downloaded(&1))
+  end
+
+  def is_downloaded(path) do
+    suffix = Application.get_env(:onigumo, :downloaded_suffix)
+    Path.extname(path) == suffix
+  end
+end
diff --git a/test/onigumo_parser_test.exs b/test/onigumo_parser_test.exs
new file mode 100644
index 0000000..c225f92
--- /dev/null
+++ b/test/onigumo_parser_test.exs
@@ -0,0 +1,72 @@
+defmodule OnigumoParserTest do
+  use ExUnit.Case
+  import Mox
+
+  @suffixes [
+    ".json",
+    ""
+  ]
+
+  @files [
+    {[], []},
+    {["first", "second"], []},
+    {["first"], ["second"]},
+    {[], ["first", "second"]},
+  ]
+
+  setup(:verify_on_exit!)
+
+  describe("Onigumo.Parser.main/1") do
+    @tag :tmp_dir
+    test("run Parser", %{tmp_dir: tmp_dir}) do
+      _result = Onigumo.Parser.main(tmp_dir)
+      assert(false)  # TODO: Do!
+    end
+
+    @tag :tmp_dir
+    test("return :ok", %{tmp_dir: tmp_dir}) do
+      result = Onigumo.Parser.main(tmp_dir)
+      assert(result == :ok)
+    end
+  end
+
+  describe("Onigumo.Parser.list_downloaded/1") do
+    for {expected, unexpected} <- @files do
+      @tag :tmp_dir
+      test("list a directory expecting #{inspect(expected)} and not expecting #{inspect(unexpected)}", %{tmp_dir: tmp_dir}) do
+        suffix = Application.get_env(:onigumo, :downloaded_suffix)
+
+        expected = Enum.map(unquote(expected), fn file ->
+          file <> suffix
+        end)
+
+        Enum.map(expected ++ unquote(unexpected), fn file ->
+          path = Path.join(tmp_dir, file)
+          File.write!(path, "")
+        end)
+
+        result = Onigumo.Parser.list_downloaded(tmp_dir)
+        assert(MapSet.new(result) == MapSet.new(expected))
+      end
+    end
+  end
+
+  describe("Onigumo.Parser.is_downloaded/1") do
+    test("recognize a downloaded file") do
+      suffix = Application.get_env(:onigumo, :downloaded_suffix)
+      path = "/test_dir/test_file#{suffix}"
+
+      result = Onigumo.Parser.is_downloaded(path)
+      assert(result == true)
+    end
+
+    for suffix <- @suffixes do
+      test("do not recognize another file #{inspect(suffix)}") do
+        path = "/test_dir/test_file#{unquote(suffix)}"
+
+        result = Onigumo.Parser.is_downloaded(path)
+        assert(result == false)
+      end
+    end
+  end
+end