diff --git a/lib/blanks.ex b/lib/blanks.ex
index 6e8a73e..a5992e9 100644
--- a/lib/blanks.ex
+++ b/lib/blanks.ex
@@ -1,4 +1,5 @@
 defmodule Blanks do
+  @moduledoc false
   def replace(ast, replacements) do
     replacements = List.wrap(replacements)
 
diff --git a/lib/display.ex b/lib/display.ex
index 3bd83e8..5a6710c 100644
--- a/lib/display.ex
+++ b/lib/display.ex
@@ -1,4 +1,5 @@
 defmodule Display do
+  @moduledoc false
   use GenServer
 
   alias IO.ANSI
@@ -20,7 +21,7 @@ defmodule Display do
     {:noreply, %{state | clear_screen: false}}
   end
 
-  def handle_cast(:clear_screen, state = %{clear_screen: true}) do
+  def handle_cast(:clear_screen, %{clear_screen: true} = state) do
     IO.puts(ANSI.clear())
     IO.puts(ANSI.home())
 
diff --git a/lib/display/colours.ex b/lib/display/colours.ex
index 34e8d0b..0e81bcf 100644
--- a/lib/display/colours.ex
+++ b/lib/display/colours.ex
@@ -1,4 +1,5 @@
 defmodule Display.Paint do
+  @moduledoc false
   def red(str), do: painter().red(str)
   def cyan(str), do: painter().cyan(str)
   def green(str), do: painter().green(str)
@@ -13,6 +14,7 @@ defmodule Display.Paint do
 end
 
 defmodule Display.Colours do
+  @moduledoc false
   alias IO.ANSI
 
   def red(str), do: colourize(ANSI.red(), str)
@@ -26,6 +28,7 @@ defmodule Display.Colours do
 end
 
 defmodule Display.Uncoloured do
+  @moduledoc false
   def red(str), do: str
   def cyan(str), do: str
   def green(str), do: str
diff --git a/lib/display/failure.ex b/lib/display/failure.ex
index ced1046..57f1e62 100644
--- a/lib/display/failure.ex
+++ b/lib/display/failure.ex
@@ -1,4 +1,5 @@
 defmodule Display.Failure do
+  @moduledoc false
   alias Display.Paint
 
   @no_value :ex_unit_no_meaningful_value
diff --git a/lib/display/intro.ex b/lib/display/intro.ex
index df36542..32ce92d 100644
--- a/lib/display/intro.ex
+++ b/lib/display/intro.ex
@@ -1,11 +1,12 @@
 defmodule Display.Intro do
+  @moduledoc false
   alias Display.Paint
 
   def intro(module, modules) do
-    if not (module in modules) do
-      show_intro(module.intro)
-    else
+    if module in modules do
       ""
+    else
+      show_intro(module.intro)
     end
   end
 
diff --git a/lib/display/notification.ex b/lib/display/notification.ex
index 6826b22..bd7fdce 100644
--- a/lib/display/notification.ex
+++ b/lib/display/notification.ex
@@ -1,4 +1,5 @@
 defmodule Display.Notifications do
+  @moduledoc false
   alias Display.Paint
 
   def congratulate do
@@ -13,8 +14,7 @@ defmodule Display.Notifications do
   defp module_names(modules) do
     modules
     |> Enum.map(&Atom.to_string/1)
-    |> Enum.map(&name/1)
-    |> Enum.join(", ")
+    |> Enum.map_join(", ", &name/1)
     |> Paint.red()
   end
 
diff --git a/lib/display/progress_bar.ex b/lib/display/progress_bar.ex
index 6163e97..1c029ba 100644
--- a/lib/display/progress_bar.ex
+++ b/lib/display/progress_bar.ex
@@ -1,4 +1,5 @@
 defmodule Display.ProgressBar do
+  @moduledoc false
   @progress_bar_length 30
 
   def progress_bar(%{current: current, total: total}) do
diff --git a/lib/elixir_koans.ex b/lib/elixir_koans.ex
index 6de4a5e..dcf857f 100644
--- a/lib/elixir_koans.ex
+++ b/lib/elixir_koans.ex
@@ -1,4 +1,5 @@
 defmodule ElixirKoans do
+  @moduledoc false
   use Application
 
   def start(_type, _args) do
diff --git a/lib/execute.ex b/lib/execute.ex
index 485e0c5..6c46273 100644
--- a/lib/execute.ex
+++ b/lib/execute.ex
@@ -1,4 +1,5 @@
 defmodule Execute do
+  @moduledoc false
   def run_module(module, callback \\ fn _result, _module, _koan -> nil end) do
     Enum.reduce_while(module.all_koans, :passed, fn koan, _ ->
       module
diff --git a/lib/koans.ex b/lib/koans.ex
index 5ab03b3..efb1504 100644
--- a/lib/koans.ex
+++ b/lib/koans.ex
@@ -1,4 +1,5 @@
 defmodule Koans do
+  @moduledoc false
   defp valid_name(name) do
     Regex.match?(~r/([A-Z]|\.\.\.).+/, name)
   end
diff --git a/lib/koans/01_equalities.ex b/lib/koans/01_equalities.ex
index 142ed7c..06f77fb 100644
--- a/lib/koans/01_equalities.ex
+++ b/lib/koans/01_equalities.ex
@@ -1,4 +1,5 @@
 defmodule Equalities do
+  @moduledoc false
   use Koans
 
   @intro """
diff --git a/lib/koans/02_strings.ex b/lib/koans/02_strings.ex
index 2eb6aad..05f4d8f 100644
--- a/lib/koans/02_strings.ex
+++ b/lib/koans/02_strings.ex
@@ -1,4 +1,5 @@
 defmodule Strings do
+  @moduledoc false
   use Koans
 
   @intro "Strings"
diff --git a/lib/koans/03_numbers.ex b/lib/koans/03_numbers.ex
index faed1ce..9fb3ab2 100644
--- a/lib/koans/03_numbers.ex
+++ b/lib/koans/03_numbers.ex
@@ -1,4 +1,5 @@
 defmodule Numbers do
+  @moduledoc false
   require Integer
   use Koans
 
@@ -49,7 +50,7 @@ defmodule Numbers do
   end
 
   koan "Let's grab the individual digits in a list" do
-    individual_digits = Integer.digits(58127)
+    individual_digits = Integer.digits(58_127)
     assert individual_digits == ___
   end
 
diff --git a/lib/koans/04_atoms.ex b/lib/koans/04_atoms.ex
index a6a3199..e535355 100644
--- a/lib/koans/04_atoms.ex
+++ b/lib/koans/04_atoms.ex
@@ -1,4 +1,5 @@
 defmodule Atoms do
+  @moduledoc false
   use Koans
 
   @intro "Atoms"
diff --git a/lib/koans/05_tuples.ex b/lib/koans/05_tuples.ex
index ec79557..70a65bb 100644
--- a/lib/koans/05_tuples.ex
+++ b/lib/koans/05_tuples.ex
@@ -1,4 +1,5 @@
 defmodule Tuples do
+  @moduledoc false
   use Koans
 
   @intro "Tuples"
diff --git a/lib/koans/06_lists.ex b/lib/koans/06_lists.ex
index dd6c8a9..2170774 100644
--- a/lib/koans/06_lists.ex
+++ b/lib/koans/06_lists.ex
@@ -1,4 +1,5 @@
 defmodule Lists do
+  @moduledoc false
   use Koans
 
   @intro "Lists"
diff --git a/lib/koans/07_keyword_lists.ex b/lib/koans/07_keyword_lists.ex
index 8c233ba..ba53431 100644
--- a/lib/koans/07_keyword_lists.ex
+++ b/lib/koans/07_keyword_lists.ex
@@ -1,4 +1,5 @@
 defmodule KeywordLists do
+  @moduledoc false
   use Koans
 
   @intro "KeywordLists"
diff --git a/lib/koans/08_maps.ex b/lib/koans/08_maps.ex
index 96e8a78..a82237a 100644
--- a/lib/koans/08_maps.ex
+++ b/lib/koans/08_maps.ex
@@ -1,4 +1,5 @@
 defmodule Maps do
+  @moduledoc false
   use Koans
 
   @intro "Maps"
diff --git a/lib/koans/09_map_sets.ex b/lib/koans/09_map_sets.ex
index 79d8038..4f3ed99 100644
--- a/lib/koans/09_map_sets.ex
+++ b/lib/koans/09_map_sets.ex
@@ -1,4 +1,5 @@
 defmodule MapSets do
+  @moduledoc false
   use Koans
 
   @intro "My name is Set, MapSet."
diff --git a/lib/koans/10_structs.ex b/lib/koans/10_structs.ex
index b05df3d..8e9b780 100644
--- a/lib/koans/10_structs.ex
+++ b/lib/koans/10_structs.ex
@@ -1,9 +1,11 @@
 defmodule Structs do
+  @moduledoc false
   use Koans
 
   @intro "Structs"
 
   defmodule Person do
+    @moduledoc false
     defstruct [:name, :age]
   end
 
@@ -35,10 +37,12 @@ defmodule Structs do
   end
 
   defmodule Plane do
+    @moduledoc false
     defstruct passengers: 0, maker: :boeing
   end
 
   defmodule Airline do
+    @moduledoc false
     defstruct plane: %Plane{}, name: "Southwest"
   end
 
diff --git a/lib/koans/11_sigils.ex b/lib/koans/11_sigils.ex
index b297f56..d22c885 100644
--- a/lib/koans/11_sigils.ex
+++ b/lib/koans/11_sigils.ex
@@ -1,4 +1,5 @@
 defmodule Sigils do
+  @moduledoc false
   use Koans
 
   @intro "Sigils"
diff --git a/lib/koans/12_pattern_matching.ex b/lib/koans/12_pattern_matching.ex
index bee3822..e43c92b 100644
--- a/lib/koans/12_pattern_matching.ex
+++ b/lib/koans/12_pattern_matching.ex
@@ -1,4 +1,5 @@
 defmodule PatternMatching do
+  @moduledoc false
   use Koans
 
   @intro "PatternMatching"
@@ -94,6 +95,7 @@ defmodule PatternMatching do
   end
 
   defmodule Animal do
+    @moduledoc false
     defstruct [:kind, :name]
   end
 
@@ -103,6 +105,7 @@ defmodule PatternMatching do
   end
 
   defmodule Plane do
+    @moduledoc false
     defstruct passengers: 0, maker: :boeing
   end
 
diff --git a/lib/koans/13_functions.ex b/lib/koans/13_functions.ex
index d5d5cf1..a9c6350 100644
--- a/lib/koans/13_functions.ex
+++ b/lib/koans/13_functions.ex
@@ -1,4 +1,5 @@
 defmodule Functions do
+  @moduledoc false
   use Koans
 
   @intro "Functions"
@@ -104,8 +105,7 @@ defmodule Functions do
     result =
       "full-name"
       |> String.split("-")
-      |> Enum.map(&String.capitalize/1)
-      |> Enum.join(" ")
+      |> Enum.map_join(" ", &String.capitalize/1)
 
     assert result == ___
   end
diff --git a/lib/koans/14_enums.ex b/lib/koans/14_enums.ex
index 78525cd..e158aa7 100644
--- a/lib/koans/14_enums.ex
+++ b/lib/koans/14_enums.ex
@@ -1,4 +1,5 @@
 defmodule Enums do
+  @moduledoc false
   use Koans
 
   @intro "Enums"
diff --git a/lib/koans/15_processes.ex b/lib/koans/15_processes.ex
index 51fe2f7..e0ea6eb 100644
--- a/lib/koans/15_processes.ex
+++ b/lib/koans/15_processes.ex
@@ -1,4 +1,5 @@
 defmodule Processes do
+  @moduledoc false
   use Koans
 
   @intro "Processes"
@@ -88,8 +89,12 @@ defmodule Processes do
 
     send(pid, {:hello, self()})
 
-    timeout = 100 # ms
-    failure_message = "Sorry, I didn't get the right message. Look at the message that is sent back very closely, and try again"
+    # ms
+    timeout = 100
+
+    failure_message =
+      "Sorry, I didn't get the right message. Look at the message that is sent back very closely, and try again"
+
     assert_receive ___, timeout, failure_message
   end
 
diff --git a/lib/koans/16_tasks.ex b/lib/koans/16_tasks.ex
index c32837c..1364ff0 100644
--- a/lib/koans/16_tasks.ex
+++ b/lib/koans/16_tasks.ex
@@ -1,4 +1,5 @@
 defmodule Tasks do
+  @moduledoc false
   use Koans
 
   @intro "Tasks"
diff --git a/lib/koans/17_agents.ex b/lib/koans/17_agents.ex
index c6e17f2..af9c08b 100644
--- a/lib/koans/17_agents.ex
+++ b/lib/koans/17_agents.ex
@@ -1,4 +1,5 @@
 defmodule Agents do
+  @moduledoc false
   use Koans
 
   @intro "Agents"
diff --git a/lib/koans/18_genservers.ex b/lib/koans/18_genservers.ex
index ab6d7dc..752a4f4 100644
--- a/lib/koans/18_genservers.ex
+++ b/lib/koans/18_genservers.ex
@@ -1,9 +1,11 @@
 defmodule GenServers do
+  @moduledoc false
   use Koans
 
   @intro "GenServers"
 
   defmodule Laptop do
+    @moduledoc false
     use GenServer
 
     #####
diff --git a/lib/koans/19_protocols.ex b/lib/koans/19_protocols.ex
index 5b19d56..3d36158 100644
--- a/lib/koans/19_protocols.ex
+++ b/lib/koans/19_protocols.ex
@@ -1,4 +1,5 @@
 defmodule Protocols do
+  @moduledoc false
   use Koans
 
   @intro "Want to follow the rules? Adhere to the protocol!"
@@ -12,13 +13,25 @@ defmodule Protocols do
   end
 
   defmodule Painter do
+    @moduledoc false
     @derive Artist
     defstruct name: ""
   end
 
-  defmodule(Musician, do: defstruct(name: "", instrument: ""))
-  defmodule(Dancer, do: defstruct(name: "", dance_style: ""))
-  defmodule(Physicist, do: defstruct(name: ""))
+  defmodule Musician do
+    @moduledoc false
+    defstruct(name: "", instrument: "")
+  end
+
+  defmodule Dancer do
+    @moduledoc false
+    defstruct(name: "", dance_style: "")
+  end
+
+  defmodule Physicist do
+    @moduledoc false
+    defstruct(name: "")
+  end
 
   defimpl Artist, for: Musician do
     def perform(musician) do
diff --git a/lib/koans/20_comprehensions.ex b/lib/koans/20_comprehensions.ex
index f0ba2e3..2ccc7a9 100644
--- a/lib/koans/20_comprehensions.ex
+++ b/lib/koans/20_comprehensions.ex
@@ -1,32 +1,32 @@
 defmodule Comprehensions do
+  @moduledoc false
   use Koans
 
   @intro "A comprehension is made of three parts: generators, filters, and collectibles. We will look at how these interact with each other"
 
   koan "The generator, `n <- [1, 2, 3, 4]`, is providing the values for our comprehension" do
-    assert (for n <- [1, 2, 3, 4], do: n * n) == ___
+    assert for(n <- [1, 2, 3, 4], do: n * n) == ___
   end
 
   koan "Any enumerable can be a generator" do
-    assert (for n <- 1..4, do: n * n) == ___
+    assert for(n <- 1..4, do: n * n) == ___
   end
 
   koan "A generator specifies how to extract values from a collection" do
-    collection = [["Hello","World"], ["Apple", "Pie"]]
-    assert (for [a, b] <- collection, do: "#{a} #{b}") == ___
+    collection = [["Hello", "World"], ["Apple", "Pie"]]
+    assert for([a, b] <- collection, do: "#{a} #{b}") == ___
   end
 
   koan "You can use multiple generators at once" do
-    assert (for x <- ["little", "big"], y <- ["dogs", "cats"], do: "#{x} #{y}") == ___
+    assert for(x <- ["little", "big"], y <- ["dogs", "cats"], do: "#{x} #{y}") == ___
   end
 
   koan "Use a filter to reduce your work" do
-    assert (for n <- [1, 2, 3, 4, 5, 6], n > 3, do: n) == ___
+    assert for(n <- [1, 2, 3, 4, 5, 6], n > 3, do: n) == ___
   end
 
   koan "Add the result of a comprehension to an existing collection" do
     collection = for x <- ["Pecan", "Pumpkin"], into: %{}, do: {x, "#{x} Pie"}
     assert collection == ___
   end
-
 end
diff --git a/lib/meditate.ex b/lib/meditate.ex
index 161b512..bc72891 100644
--- a/lib/meditate.ex
+++ b/lib/meditate.ex
@@ -1,4 +1,5 @@
 defmodule Mix.Tasks.Meditate do
+  @moduledoc false
   use Mix.Task
 
   @shortdoc "Start the koans"
diff --git a/lib/runner.ex b/lib/runner.ex
index ad862e1..32c25d0 100644
--- a/lib/runner.ex
+++ b/lib/runner.ex
@@ -1,4 +1,5 @@
 defmodule Runner do
+  @moduledoc false
   use GenServer
 
   def koan?(koan) do
diff --git a/lib/tracker.ex b/lib/tracker.ex
index c02885c..80f64c2 100644
--- a/lib/tracker.ex
+++ b/lib/tracker.ex
@@ -1,4 +1,5 @@
 defmodule Tracker do
+  @moduledoc false
   alias __MODULE__
 
   defstruct total: 0,
diff --git a/lib/watcher.ex b/lib/watcher.ex
index c8181a4..32ddaf6 100644
--- a/lib/watcher.ex
+++ b/lib/watcher.ex
@@ -1,4 +1,5 @@
 defmodule Watcher do
+  @moduledoc false
   use GenServer
 
   def start_link() do
diff --git a/mix.exs b/mix.exs
index ac553bb..de88079 100644
--- a/mix.exs
+++ b/mix.exs
@@ -15,7 +15,8 @@ defmodule Koans.Mixfile do
   end
 
   defp deps do
-    [{:file_system, "~> 0.2"}]
+    [{:file_system, "~> 0.2"},
+    {:credo, "~> 1.7", only: [:dev, :test], runtime: false}]
   end
 
   defp elixirc_path(:test), do: ["lib/", "test/support"]
diff --git a/mix.lock b/mix.lock
index 089c5a0..3acd105 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,3 +1,6 @@
 %{
+  "bunt": {:hex, :bunt, "0.2.1", "e2d4792f7bc0ced7583ab54922808919518d0e57ee162901a16a1b6664ef3b14", [:mix], [], "hexpm", "a330bfb4245239787b15005e66ae6845c9cd524a288f0d141c148b02603777a5"},
+  "credo": {:hex, :credo, "1.7.1", "6e26bbcc9e22eefbff7e43188e69924e78818e2fe6282487d0703652bc20fd62", [:mix], [{:bunt, "~> 0.2.1", [hex: :bunt, repo: "hexpm", optional: false]}, {:file_system, "~> 0.2.8", [hex: :file_system, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "e9871c6095a4c0381c89b6aa98bc6260a8ba6addccf7f6a53da8849c748a58a2"},
   "file_system": {:hex, :file_system, "0.2.10", "fb082005a9cd1711c05b5248710f8826b02d7d1784e7c3451f9c1231d4fc162d", [:mix], [], "hexpm", "41195edbfb562a593726eda3b3e8b103a309b733ad25f3d642ba49696bf715dc"},
+  "jason": {:hex, :jason, "1.4.1", "af1504e35f629ddcdd6addb3513c3853991f694921b1b9368b0bd32beb9f1b63", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "fbb01ecdfd565b56261302f7e1fcc27c4fb8f32d56eab74db621fc154604a7a1"},
 }
diff --git a/test/blanks_test.exs b/test/blanks_test.exs
index 74fef77..f264d84 100644
--- a/test/blanks_test.exs
+++ b/test/blanks_test.exs
@@ -19,7 +19,7 @@ defmodule BlanksTest do
   end
 
   test "multiple arguments" do
-    ast = quote do: assert(___ == ___)
+    ast = quote do: assert true == false
 
     assert Blanks.replace(ast, [true, false]) == quote(do: assert(true == false))
   end
@@ -43,7 +43,7 @@ defmodule BlanksTest do
   end
 
   test "counts multiple blanks" do
-    ast = quote do: assert(___ == ___)
+    ast = quote do: assert ___ == ___
 
     assert Blanks.count(ast) == 2
   end
diff --git a/test/display/failure_test.exs b/test/display/failure_test.exs
index addce2c..07f9b2a 100644
--- a/test/display/failure_test.exs
+++ b/test/display/failure_test.exs
@@ -39,7 +39,7 @@ defmodule FailureTests do
 
   test "only offending lines are displayed for errors" do
     [koan] = SingleArity.all_koans()
-    error = apply(SingleArity, koan, []) |> Tuple.to_list |> List.last |> error
+    error = apply(SingleArity, koan, []) |> Tuple.to_list() |> List.last() |> error
 
     assert Failure.format_failure(error) == """
            Assertion failed in some_file.ex:42\nmatch?(:foo, ___)
diff --git a/test/executor_test.exs b/test/executor_test.exs
index d989123..629c1ee 100644
--- a/test/executor_test.exs
+++ b/test/executor_test.exs
@@ -8,7 +8,7 @@ defmodule ExecuteTest do
   test "stops at the first failing koan" do
     {:failed, %{file: file, line: line}, SampleKoan, _name} = Execute.run_module(SampleKoan)
     assert file == 'test/support/sample_koan.ex'
-    assert line == 8
+    assert line == 9
   end
 
   test "can access intro" do
diff --git a/test/koans/comprehensions_koans_test.exs b/test/koans/comprehensions_koans_test.exs
index 22f056f..f8d851b 100644
--- a/test/koans/comprehensions_koans_test.exs
+++ b/test/koans/comprehensions_koans_test.exs
@@ -1,18 +1,17 @@
-defmodule ComprehensionsTests do
-  use ExUnit.Case
-  import TestHarness
-
-  test "Comprehensions" do
-    answers = [
-      [1, 4, 9, 16],
-      [1, 4, 9, 16],
-      ["Hello World", "Apple Pie"],
-      ["little dogs", "little cats", "big dogs", "big cats"],
-      [4, 5, 6],
-      %{"Pecan" => "Pecan Pie", "Pumpkin" => "Pumpkin Pie"}
-    ]
-
-    test_all(Comprehensions, answers)
-  end
-
-end
+defmodule ComprehensionsTests do
+  use ExUnit.Case
+  import TestHarness
+
+  test "Comprehensions" do
+    answers = [
+      [1, 4, 9, 16],
+      [1, 4, 9, 16],
+      ["Hello World", "Apple Pie"],
+      ["little dogs", "little cats", "big dogs", "big cats"],
+      [4, 5, 6],
+      %{"Pecan" => "Pecan Pie", "Pumpkin" => "Pumpkin Pie"}
+    ]
+
+    test_all(Comprehensions, answers)
+  end
+end
diff --git a/test/support/passing_koan.ex b/test/support/passing_koan.ex
index 117092f..8b7bb9c 100644
--- a/test/support/passing_koan.ex
+++ b/test/support/passing_koan.ex
@@ -1,4 +1,5 @@
 defmodule PassingKoan do
+  @moduledoc false
   use Koans
 
   @intro "something"
diff --git a/test/support/sample_koan.ex b/test/support/sample_koan.ex
index 3af89ca..f4ac3ee 100644
--- a/test/support/sample_koan.ex
+++ b/test/support/sample_koan.ex
@@ -1,4 +1,5 @@
 defmodule SampleKoan do
+  @moduledoc false
   use Koans
 
   @intro """
diff --git a/test/support/single_arity_koan.ex b/test/support/single_arity_koan.ex
index 0fe5aa5..ebe50aa 100644
--- a/test/support/single_arity_koan.ex
+++ b/test/support/single_arity_koan.ex
@@ -1,4 +1,5 @@
 defmodule SingleArity do
+  @moduledoc false
   use Koans
 
   @intro """
diff --git a/test/test_helper.exs b/test/test_helper.exs
index 2006538..b7c383e 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -1,4 +1,5 @@
-timeout = 1000 # ms
+# ms
+timeout = 1000
 ExUnit.start(timeout: timeout)
 
 defmodule TestHarness do