diff --git a/lib/mix_tasks.ex b/lib/mix_tasks.ex
index 45ed17a..6d7d90f 100644
--- a/lib/mix_tasks.ex
+++ b/lib/mix_tasks.ex
@@ -100,6 +100,25 @@ defmodule Mix.Tasks.Aoc do
     create_file("#{tests_dir(day)}#{test}.#{part}", IO.read(:stdio, :eof))
   end
 
+  defp run(day, ["test", "watch"]) do
+    {:ok, pid} = Mix.Tasks.Aoc.Watcher.start_link({[dirs: ["lib/", "test/day#{day}/"]], self()})
+    Process.monitor(pid)
+    loop = fn (loop) ->
+      IO.puts(IO.ANSI.clear() <> IO.ANSI.cursor(0, 0))
+      IO.puts "At #{DateTime.utc_now(:second)}:"
+      System.shell("mix compile")
+      :code.purge(module(day))
+      :code.purge(Aoc2023.Common)
+      :code.load_file(module(day))
+      run(day, ["test"])
+      receive do
+        :update -> loop.(loop)
+        {:DOWN, _, :process, ^pid, _} -> nil
+      end
+    end
+    loop.(loop)
+  end
+
   defp run(day, ["test"]) do
     mod = module(day)
     tests = tests(day)
@@ -166,4 +185,28 @@ defmodule Mix.Tasks.Aoc do
   defp run_file(day, file \\ nil) do
     module(day).main(if file, do: read(file), else: IO.read(:stdio, :eof))
   end
+
+
+  defmodule Watcher do
+    use GenServer
+
+    def start_link(args) do
+      GenServer.start_link(__MODULE__, args)
+    end
+
+    def init({args, callback}) do
+      {:ok, watcher_pid} = FileSystem.start_link(args)
+      FileSystem.subscribe(watcher_pid)
+      {:ok, %{watcher_pid: watcher_pid, callback: callback}}
+    end
+
+    def handle_info({:file_event, watcher_pid, {_path, _events}}, %{watcher_pid: watcher_pid, callback: callback} = state) do
+      send(callback, :update)
+      {:noreply, state}
+    end
+
+    def handle_info({:file_event, _watcher_pid, :stop}, state) do
+      {:noreply, state}
+    end
+  end
 end
diff --git a/mix.exs b/mix.exs
index dbe42ef..fda6d51 100644
--- a/mix.exs
+++ b/mix.exs
@@ -19,7 +19,8 @@ defmodule Aoc2023.MixProject do
 
   defp deps do
     [
-      {:httpoison, "~> 2.0"}
+      httpoison: "~> 2.0",
+      file_system: "~> 1.0"
     ]
   end
 end
diff --git a/mix.lock b/mix.lock
index 14e8515..41c7099 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,5 +1,6 @@
 %{
   "certifi": {:hex, :certifi, "2.12.0", "2d1cca2ec95f59643862af91f001478c9863c2ac9cb6e2f89780bfd8de987329", [:rebar3], [], "hexpm", "ee68d85df22e554040cdb4be100f33873ac6051387baf6a8f6ce82272340ff1c"},
+  "file_system": {:hex, :file_system, "1.0.0", "b689cc7dcee665f774de94b5a832e578bd7963c8e637ef940cd44327db7de2cd", [:mix], [], "hexpm", "6752092d66aec5a10e662aefeed8ddb9531d79db0bc145bb8c40325ca1d8536d"},
   "hackney": {:hex, :hackney, "1.20.1", "8d97aec62ddddd757d128bfd1df6c5861093419f8f7a4223823537bad5d064e2", [:rebar3], [{:certifi, "~> 2.12.0", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "~> 6.1.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "~> 1.0.0", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~> 1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.4.1", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "~> 1.1.0", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}, {:unicode_util_compat, "~> 0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "fe9094e5f1a2a2c0a7d10918fee36bfec0ec2a979994cff8cfe8058cd9af38e3"},
   "httpoison": {:hex, :httpoison, "2.2.1", "87b7ed6d95db0389f7df02779644171d7319d319178f6680438167d7b69b1f3d", [:mix], [{:hackney, "~> 1.17", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "51364e6d2f429d80e14fe4b5f8e39719cacd03eb3f9a9286e61e216feac2d2df"},
   "idna": {:hex, :idna, "6.1.1", "8a63070e9f7d0c62eb9d9fcb360a7de382448200fbbd1b106cc96d3d8099df8d", [:rebar3], [{:unicode_util_compat, "~> 0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "92376eb7894412ed19ac475e4a86f7b413c1b9fbb5bd16dccd57934157944cea"},