diff --git a/.formatter.exs b/.formatter.exs
index 7539791..061dc09 100644
--- a/.formatter.exs
+++ b/.formatter.exs
@@ -1,5 +1,5 @@
 [
-  line_length: 300,
+  line_length: 150,
   import_deps: [:phoenix],
   inputs: ["*.{ex,exs}", "{config,lib,test}/**/*.{ex,exs}"]
 ]
diff --git a/lib/ksuite_middleware/ksuite_client.ex b/lib/ksuite_middleware/ksuite_client.ex
index 186dc96..db12c36 100644
--- a/lib/ksuite_middleware/ksuite_client.ex
+++ b/lib/ksuite_middleware/ksuite_client.ex
@@ -5,7 +5,7 @@ defmodule KsuiteMiddleware.KsuiteClient do
 
   require Logger
 
-  plug Tesla.Middleware.BaseUrl, "https://api.infomaniak.com"
+  plug Tesla.Middleware.BaseUrl, State.get_ksuite_api_server()
   plug Tesla.Middleware.Logger, debug: false
   plug Tesla.Middleware.PathParams
   plug Tesla.Middleware.Headers, [{"User-Agent", "ksuite-middleware"}]
diff --git a/lib/ksuite_middleware/state.ex b/lib/ksuite_middleware/state.ex
index 11b78b6..f9aea8a 100644
--- a/lib/ksuite_middleware/state.ex
+++ b/lib/ksuite_middleware/state.ex
@@ -18,6 +18,9 @@ defmodule KsuiteMiddleware.State do
   @spec get_timezone() :: Timex.TimezoneInfo.t()
   def get_timezone(), do: GenServer.call(State, :get_timezone)
 
+  @spec get_ksuite_api_server() :: String.t()
+  def get_ksuite_api_server(), do: "https://api.infomaniak.com"
+
   # Callbacks
 
   @impl true
diff --git a/lib/ksuite_middleware_web/controllers/calendar_controller.ex b/lib/ksuite_middleware_web/controllers/calendar_controller.ex
index 4824444..b92a01b 100644
--- a/lib/ksuite_middleware_web/controllers/calendar_controller.ex
+++ b/lib/ksuite_middleware_web/controllers/calendar_controller.ex
@@ -7,6 +7,8 @@ defmodule KsuiteMiddlewareWeb.CalendarController do
 
   require Logger
 
+  action_fallback KsuiteMiddleware.FallbackController
+
   def get_events(conn, %{"from" => from, "to" => to, "calendar_id" => calendar_id}),
     do:
       parse_params(from, to, calendar_id)
@@ -14,6 +16,13 @@ defmodule KsuiteMiddlewareWeb.CalendarController do
       |> then(&translate_to_events/1)
       |> then(&send_response(conn, &1))
 
+  def get_events(conn, _),
+    do:
+      conn
+      |> put_status(:bad_request)
+      |> put_resp_content_type("application/problem+json")
+      |> render(:"400", reason: "The arguments were missing.")
+
   # Private
 
   defp read_events({:error, error, reason}), do: {:error, error, reason}
@@ -28,19 +37,28 @@ defmodule KsuiteMiddlewareWeb.CalendarController do
     client |> CalDAVClient.Event.get_events(calendar_url, from, to)
   end
 
-  defp send_response(conn, {:ok, events}), do: json(conn, events)
+  defp send_response(conn, {:ok, events}),
+    do: render(conn, :events, events: events)
 
-  defp send_response(conn, {:error, error, reason}),
+  defp send_response(conn, {:error, :bad_request, reason}),
     do:
       conn
-      |> put_status(error)
-      |> json(%{reason: reason})
+      |> put_status(:bad_request)
+      |> put_resp_content_type("application/problem+json")
+      |> render(:"400", reason: reason)
+
+  defp send_response(conn, {:error, :not_found, reason}),
+    do:
+      conn
+      |> put_status(:not_found)
+      |> put_resp_content_type("application/problem+json")
+      |> render(:"404", reason: reason)
 
   defp send_response(conn, {:error, reason}),
     do:
       conn
-      |> put_status(500)
-      |> json(%{reason: reason})
+      |> put_status(:internal_server_error)
+      |> render(:"500", reason: reason)
 
   defp parse_params(from, to, calendar_id) do
     Logger.info("Parsing the arguments ...")
@@ -50,9 +68,10 @@ defmodule KsuiteMiddlewareWeb.CalendarController do
          {:ok, calendar_id} <- parse_calendar_id(calendar_id) do
       {:ok, from, to, calendar_id}
     else
-      :invalid_to -> {:error, :bad_request, "The argument 'to' was invalid."}
-      :invalid_from -> {:error, :bad_request, "The argument 'from' was invalid."}
+      {:invalid_to, reason} -> {:error, :bad_request, "The argument 'to' was invalid. #{reason}"}
+      {:invalid_from, reason} -> {:error, :bad_request, "The argument 'from' was invalid. #{reason}"}
       {:invalid_calendar_id, reason} -> {:error, :bad_request, reason}
+      _ -> {:error, :internal_server_error, "Unhandled error occured"}
     end
   end
 
@@ -60,18 +79,20 @@ defmodule KsuiteMiddlewareWeb.CalendarController do
   defp parse_calendar_id(_), do: {:invalid_calendar_id, "The calendar_id was too long."}
 
   defp parse_datetime(error_atom, datetime) when is_atom(error_atom) and is_bitstring(datetime) do
-    case Timex.parse!(datetime, "{ISO:Extended:Z}") do
-      %DateTime{} = x -> {:ok, x}
-      _ -> error_atom
+    case Timex.parse(datetime, "{ISO:Extended:Z}") do
+      {:ok, %DateTime{} = x} -> {:ok, x}
+      {:error, reason} -> {error_atom, reason}
     end
   end
 
-  defp translate_to_events({:error, :unauthorized}), do: {:error, :unauthorized, "Unauthorized access to the CalDAV server, double check your credentials."}
+  defp translate_to_events({:error, :unauthorized}),
+    do: {:error, :unauthorized, "Unauthorized access to the CalDAV server, double check your credentials."}
+
   defp translate_to_events({:error, :not_found}), do: {:error, :not_found, "The given calendar_id was not found in the given server CalDAV."}
   defp translate_to_events({:error, reason}), do: {:error, reason}
   defp translate_to_events({:error, error, reason}), do: {:error, error, reason}
   defp translate_to_events({:ok, []}), do: {:ok, []}
-  defp translate_to_events({:ok, icalendar_events}), do: translate_to_events(icalendar_events, [])
+  defp translate_to_events({:ok, [%CalDAVClient.Event{} | _] = icalendar_events}), do: translate_to_events(icalendar_events, [])
   defp translate_to_events([], acc) when is_list(acc), do: {:ok, acc}
 
   defp translate_to_events([head | tail], acc) when is_list(acc) do
@@ -83,7 +104,12 @@ defmodule KsuiteMiddlewareWeb.CalendarController do
     from = translate_date_to_utc(from)
     to = translate_date_to_utc(to)
 
-    new_event = %KsuiteCalendarEvent{subject: summary, from: Timex.format!(from, "{ISO:Extended:Z}"), to: Timex.format!(to, "{ISO:Extended:Z}"), description: description}
+    new_event = %KsuiteCalendarEvent{
+      subject: summary,
+      from: Timex.format!(from, "{ISO:Extended:Z}"),
+      to: Timex.format!(to, "{ISO:Extended:Z}"),
+      description: description
+    }
 
     translate_to_events(tail, [new_event | acc])
   end
diff --git a/lib/ksuite_middleware_web/controllers/calendar_json.ex b/lib/ksuite_middleware_web/controllers/calendar_json.ex
new file mode 100644
index 0000000..3f27c56
--- /dev/null
+++ b/lib/ksuite_middleware_web/controllers/calendar_json.ex
@@ -0,0 +1,25 @@
+defmodule KsuiteMiddlewareWeb.CalendarJSON do
+  alias KsuiteMiddlewareWeb.Models.KsuiteCalendarEvent
+
+  def events(%{events: [%KsuiteCalendarEvent{} | _] = events}), do: events
+
+  def render("400.json", %{reason: reason}),
+    do: %{title: "invalid argument", status: 400, detail: reason}
+
+  def render("404.json", %{reason: reason}),
+    do: %{
+      title: "not found",
+      status: 404,
+      detail: reason,
+      description:
+        "Oh snap! It seems we've hit a hiccup in our treasure hunt—what you seek is playing hide and seek in the " <>
+          "digital jungle! Keep those eagle eyes peeled, and perhaps try a different map or a clever keyword dance " <>
+          "to coax the elusive information out of hiding."
+    }
+
+  def render("500.json", %{reason: reason}),
+    do: %{title: "internal server error", status: 500, detail: reason}
+
+  def render(template, _assigns),
+    do: %{detail: Phoenix.Controller.status_message_from_template(template)}
+end
diff --git a/lib/ksuite_middleware_web/controllers/error_controller.ex b/lib/ksuite_middleware_web/controllers/error_controller.ex
deleted file mode 100644
index 1379a83..0000000
--- a/lib/ksuite_middleware_web/controllers/error_controller.ex
+++ /dev/null
@@ -1,9 +0,0 @@
-defmodule KsuiteMiddlewareWeb.ErrorController do
-  use KsuiteMiddlewareWeb, :controller
-
-  def not_found(conn, _params),
-    do:
-      conn
-      |> put_resp_header("content-type", "text/html; charset=utf-8")
-      |> send_file(404, Application.app_dir(:ksuite_middleware, "priv/static/not-found.html"))
-end
diff --git a/lib/ksuite_middleware_web/controllers/error_json.ex b/lib/ksuite_middleware_web/controllers/error_json.ex
index 718bb1e..33443de 100644
--- a/lib/ksuite_middleware_web/controllers/error_json.ex
+++ b/lib/ksuite_middleware_web/controllers/error_json.ex
@@ -6,6 +6,17 @@ defmodule KsuiteMiddlewareWeb.ErrorJSON do
   #   %{errors: %{detail: "Internal Server Error"}}
   # end
 
+  def render("404.json", _),
+    do: %{
+      title: "not found",
+      status: 404,
+      detail: "The resource requested was not found.",
+      description:
+        "Oh snap! It seems we've hit a hiccup in our treasure hunt—what you seek is playing hide and seek in the " <>
+          "digital jungle! Keep those eagle eyes peeled, and perhaps try a different map or a clever keyword dance " <>
+          "to coax the elusive information out of hiding."
+    }
+
   # By default, Phoenix returns the status message from
   # the template name. For example, "404.json" becomes
   # "Not Found".
diff --git a/lib/ksuite_middleware_web/controllers/fallback_controller.ex b/lib/ksuite_middleware_web/controllers/fallback_controller.ex
new file mode 100644
index 0000000..984e82f
--- /dev/null
+++ b/lib/ksuite_middleware_web/controllers/fallback_controller.ex
@@ -0,0 +1,16 @@
+defmodule KsuiteMiddlewareWeb.FallbackController do
+  @moduledoc """
+  Translates controller action results into valid `Plug.Conn` responses.
+
+  See `Phoenix.Controller.action_fallback/1` for more details.
+  """
+  use KsuiteMiddlewareWeb, :controller
+
+  # This clause is an example of how to handle resources that cannot be found.
+  def call(conn, {:error, :not_found}) do
+    conn
+    |> put_status(:not_found)
+    |> put_view(json: KsuiteMiddlewareWeb.ErrorJSON)
+    |> render(:"404")
+  end
+end
diff --git a/lib/ksuite_middleware_web/controllers/kdrive_controller.ex b/lib/ksuite_middleware_web/controllers/kdrive_controller.ex
index 895e66e..267b598 100644
--- a/lib/ksuite_middleware_web/controllers/kdrive_controller.ex
+++ b/lib/ksuite_middleware_web/controllers/kdrive_controller.ex
@@ -3,11 +3,16 @@ defmodule KsuiteMiddlewareWeb.KdriveController do
 
   alias KsuiteMiddleware.KsuiteClient
 
+  action_fallback KsuiteMiddleware.FallbackController
+
   def pass_thru(conn, %{"file_id" => id}) when is_integer(id) do
     with {:ok, response} <- KsuiteClient.download(id) do
       conn |> put_tesla_response(response)
     else
-      _ -> conn |> resp(500, "an unknown error occurred.")
+      _ ->
+        conn
+        |> put_status(:bad_gateway)
+        |> render(:"500")
     end
   end
 
@@ -16,21 +21,41 @@ defmodule KsuiteMiddlewareWeb.KdriveController do
          {:ok, response} <- KsuiteClient.download(file_id) do
       conn |> put_tesla_response(response)
     else
+      :error ->
+        conn
+        |> put_status(:bad_request)
+        |> put_resp_content_type("application/problem+json")
+        |> render(:"400", reason: :invalid_integer)
+
+      {:error, _} ->
+        conn
+        |> put_status(:bad_gateway)
+        |> put_resp_content_type("application/problem+json")
+        |> render(:"502", reason: :invalid_response_from_api)
+
       _ ->
-        conn |> resp(500, "an unknown error occurred.")
+        conn
+        |> put_status(:internal_server_error)
+        |> put_resp_content_type("application/problem+json")
+        |> render(:"500", reason: :unknown)
     end
   end
 
   def pass_thru(conn, _params),
-    do: conn |> resp(400, "The file id was missing.")
+    do:
+      conn
+      |> put_status(:bad_request)
+      |> put_resp_content_type("application/problem+json")
+      |> render(:"400", reason: :missing_file_id)
 
   # Private
 
   defp put_tesla_response(%Plug.Conn{} = conn, %Tesla.Env{status: 401}),
     do:
       conn
-      |> put_resp_header("content-type", "text/html; charset=utf-8")
-      |> send_file(400, Application.app_dir(:ksuite_middleware, "priv/static/bad-api-key.html"))
+      |> put_status(:bad_request)
+      |> put_resp_content_type("application/problem+json")
+      |> render(:"400", reason: :bad_api_key)
 
   defp put_tesla_response(%Plug.Conn{} = conn, %Tesla.Env{} = response) do
     %Tesla.Env{status: status, body: body} = response
@@ -42,7 +67,8 @@ defmodule KsuiteMiddlewareWeb.KdriveController do
     else
       _ ->
         conn
-        |> resp(status, body)
+        |> put_status(status)
+        |> render(status |> Integer.to_string() |> String.to_atom())
     end
   end
 
diff --git a/lib/ksuite_middleware_web/controllers/kdrive_json.ex b/lib/ksuite_middleware_web/controllers/kdrive_json.ex
new file mode 100644
index 0000000..d5f53d9
--- /dev/null
+++ b/lib/ksuite_middleware_web/controllers/kdrive_json.ex
@@ -0,0 +1,29 @@
+defmodule KsuiteMiddlewareWeb.KdriveJSON do
+  alias KsuiteMiddleware.State
+
+  def render("400.json", %{reason: :invalid_integer}),
+    do: %{title: "invalid argument", status: 400, detail: "The given file_id was invalid."}
+
+  def render("400.json", %{reason: :missing_file_id}),
+    do: %{title: "missing argument", status: 400, detail: "The file_id was missing."}
+
+  def render("400.json", %{reason: :bad_api_key}),
+    do: %{
+      title: "bad api key",
+      status: 400,
+      detail: "The API key is invalid, please verify the 'KSUITE_API_TOKEN'.",
+      description:
+        "Whoopsie-daisy! Looks like we got a little lost in API land. Our secret handshake seems a bit off. " <>
+          "Double-check that magic spell in the enchanted scroll labeled `KSUITE_API_TOKEN` and make sure it's been " <>
+          "properly whispered into the winds of the environment variable realm."
+    }
+
+  def render("502.json", %{reason: :invalid_response_from_api}),
+    do: %{title: "bad gateway", status: 502, detail: "The upstream api returned an invalid response.", server: State.get_ksuite_api_server()}
+
+  def render("500.json", %{reason: :unknown}),
+    do: %{title: "internal server error", status: 500, detail: "An unhandled error was returned, please contact the administrator."}
+
+  def render(template, _assigns),
+    do: %{detail: Phoenix.Controller.status_message_from_template(template)}
+end
diff --git a/lib/ksuite_middleware_web/router.ex b/lib/ksuite_middleware_web/router.ex
index 7af385b..6d60349 100644
--- a/lib/ksuite_middleware_web/router.ex
+++ b/lib/ksuite_middleware_web/router.ex
@@ -43,10 +43,4 @@ defmodule KsuiteMiddlewareWeb.Router do
       live_dashboard "/dashboard", metrics: KsuiteMiddlewareWeb.Telemetry
     end
   end
-
-  scope "/", KsuiteMiddlewareWeb do
-    pipe_through :browser
-
-    get "/*path", ErrorController, :not_found
-  end
 end
diff --git a/priv/static/bad-api-key.html b/priv/static/bad-api-key.html
deleted file mode 100644
index 4d3a76a..0000000
--- a/priv/static/bad-api-key.html
+++ /dev/null
@@ -1,53 +0,0 @@
-<!DOCTYPE html>
-<html>
-
-<head>
-    <title>Ksuite Middleware - 400</title>
-    <style>
-        body {
-            text-align: center;
-            padding: 150px;
-        }
-
-        h1 {
-            font-size: 50px;
-        }
-
-        body {
-            font: 20px Helvetica, sans-serif;
-            color: #333;
-        }
-
-        article {
-            display: block;
-            text-align: left;
-            width: 650px;
-            margin: 0 auto;
-        }
-
-        a {
-            color: #dc8100;
-            text-decoration: none;
-        }
-
-        a:hover {
-            color: #333;
-            text-decoration: none;
-        }
-    </style>
-</head>
-
-<body>
-    <article>
-        <h1>Ksuite Middleware - 400</h1>
-        <div>
-            <p>
-                Whoopsie-daisy! Looks like we got a little lost in API land. Our secret handshake seems a bit off.
-                Double-check that magic spell in the enchanted scroll labeled `KSUITE_API_TOKEN` and make sure it's been
-                properly whispered into the winds of the environment variable realm.
-            </p>
-        </div>
-    </article>
-</body>
-
-</html>
\ No newline at end of file
diff --git a/priv/static/not-found.html b/priv/static/not-found.html
deleted file mode 100644
index a6c43a4..0000000
--- a/priv/static/not-found.html
+++ /dev/null
@@ -1,53 +0,0 @@
-<!DOCTYPE html>
-<html>
-
-<head>
-    <title>Ksuite Middleware - 404</title>
-    <style>
-        body {
-            text-align: center;
-            padding: 150px;
-        }
-
-        h1 {
-            font-size: 50px;
-        }
-
-        body {
-            font: 20px Helvetica, sans-serif;
-            color: #333;
-        }
-
-        article {
-            display: block;
-            text-align: left;
-            width: 650px;
-            margin: 0 auto;
-        }
-
-        a {
-            color: #dc8100;
-            text-decoration: none;
-        }
-
-        a:hover {
-            color: #333;
-            text-decoration: none;
-        }
-    </style>
-</head>
-
-<body>
-    <article>
-        <h1>Ksuite Middleware - 404</h1>
-        <div>
-            <p>
-                Oh snap! It seems we've hit a hiccup in our treasure hunt—what you seek is playing hide and seek in the
-                digital jungle! Keep those eagle eyes peeled, and perhaps try a different map or a clever keyword dance
-                to coax the elusive information out of hiding.
-            </p>
-        </div>
-    </article>
-</body>
-
-</html>
\ No newline at end of file