diff --git a/.formatter.exs b/.formatter.exs
index d304ff3..8558637 100644
--- a/.formatter.exs
+++ b/.formatter.exs
@@ -1,3 +1,4 @@
 [
+  import_deps: [:tesla],
   inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
 ]
diff --git a/lib/ex_opentok.ex b/lib/ex_opentok.ex
index e5d7db1..0e3ab94 100644
--- a/lib/ex_opentok.ex
+++ b/lib/ex_opentok.ex
@@ -31,6 +31,10 @@ defmodule ExOpentok do
     ExOpentok.Session.init()
   end
 
+  def init! do
+    ExOpentok.Session.init!()
+  end
+
   @doc false
   def version, do: @version
 
diff --git a/lib/ex_opentok/archive.ex b/lib/ex_opentok/archive.ex
index 3fe1f08..c5275fa 100644
--- a/lib/ex_opentok/archive.ex
+++ b/lib/ex_opentok/archive.ex
@@ -81,6 +81,13 @@ defmodule ExOpentok.Archive do
     |> Client.handle_response()
   end
 
+  def stop!(archive_id) do
+    case stop(archive_id) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
+
   @doc """
   Deleting an archive
 
@@ -96,6 +103,13 @@ defmodule ExOpentok.Archive do
     |> Client.handle_response()
   end
 
+  def delete!(archive_id) do
+    case delete(archive_id) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
+
   @doc """
   Listing archives
 
@@ -133,9 +147,23 @@ defmodule ExOpentok.Archive do
     |> Client.handle_response()
   end
 
+  def list!(opts \\ %{offset: 0, count: 1000}) do
+    case list(opts) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
+
   def find(archive_id) do
     (ExOpentok.api_url() <> "#{ExOpentok.config(:key)}/archive/#{archive_id}")
     |> Client.http_request()
     |> Client.handle_response()
   end
+
+  def find!(archive_id) do
+    case find(archive_id) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
 end
diff --git a/lib/ex_opentok/client.ex b/lib/ex_opentok/client.ex
index 22dd4db..b9d4e68 100644
--- a/lib/ex_opentok/client.ex
+++ b/lib/ex_opentok/client.ex
@@ -4,14 +4,24 @@ defmodule ExOpentok.Client do
   alias ExOpentok.Token
   alias ExOpentok.Exception
 
-  plug(Tesla.Middleware.Timeout, timeout: 2_000)
+  plug Tesla.Middleware.Timeout, timeout: 2_000
+
+  plug Tesla.Middleware.Retry,
+    delay: 100,
+    max_retries: 10,
+    max_delay: 4_000,
+    should_retry: fn
+      {:ok, %{status: status}} when status >= 500 -> true
+      {:ok, _} -> false
+      {:error, _} -> true
+    end
 
   @moduledoc """
-  Wrapper for HTTPotion
+  Wrapper for Tesla
   """
 
   @doc """
-  HTTP Client's request with HTTPotion.
+  HTTP Client's request with Tesla.
   """
   def http_request(url, type \\ :get, body \\ nil) do
     do_http_request(url, type, body)
@@ -62,19 +72,26 @@ defmodule ExOpentok.Client do
   def handle_response(response) do
     case response do
       {:ok, %{status: 200, body: ""}} ->
-        %{}
+        {:ok, %{}}
 
       {:ok, %{status: 200, body: body}} ->
-        body |> Poison.decode!() |> handle_data_struct()
+        {:ok, body |> Poison.decode!() |> handle_data_struct()}
 
       {:ok, %{status: 405, body: body}} ->
-        raise "405 Method not allowed"
+        {:ok, "405 Method not allowed"}
 
       {:ok, response} ->
-        raise "Error #{response.status} -> ExOpentok query:\n #{inspect(response)}"
+        {:error, "Error #{response.status} -> ExOpentok query:\n #{inspect(response)}"}
 
       {:error, error} ->
-        raise "Error #{inspect(error)} -> ExOpentok query:\n #{inspect(response)}"
+        {:error, "Error #{inspect(error)} -> ExOpentok query:\n #{inspect(response)}"}
+    end
+  end
+
+  def handle_response!(response) do
+    case handle_response(response) do
+      {:ok, output} -> output
+      {:error, error} -> raise error
     end
   end
 
diff --git a/lib/ex_opentok/session.ex b/lib/ex_opentok/session.ex
index 1dd26c0..ba6ee40 100644
--- a/lib/ex_opentok/session.ex
+++ b/lib/ex_opentok/session.ex
@@ -34,6 +34,13 @@ defmodule ExOpentok.Session do
     |> Client.handle_response()
   end
 
+  def create!(opts) do
+    case create(opts) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
+
   # https://tokbox.com/developer/rest/#force_mute_stream
   @spec mute(String.t(), String.t()) :: %{}
   def mute(session_id, stream_id) do
@@ -42,6 +49,13 @@ defmodule ExOpentok.Session do
     |> Client.handle_response()
   end
 
+  def mute!(session_id, stream_id) do
+    case mute(session_id, stream_id) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
+
   # https://tokbox.com/developer/rest/#force_mute_session
   @spec mute_all(String.t(), [String.t()]) :: %{}
   def mute_all(session_id, excluded_stream_ids \\ []) do
@@ -55,23 +69,40 @@ defmodule ExOpentok.Session do
     |> ExOpentok.Client.handle_response()
   end
 
+  def mute_all!(session_id, excluded_stream_ids) do
+    case mute_all(session_id, excluded_stream_ids) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
+
   @spec base_session_url(String.t(), String.t()) :: String.t()
   defp base_session_url(session_id, path \\ "") do
     "https://api.opentok.com/v2/project/#{ExOpentok.config(:key)}/session/#{session_id}#{path}"
   end
 
-  defp format_response(session) do
-    Map.merge(
-      session,
-      %{
-        api_key: ExOpentok.config(:key),
-        token: Token.generate(session["session_id"])
-      }
-    )
+  defp format_response({:ok, session}) do
+    {:ok,
+     Map.merge(
+       session,
+       %{
+         api_key: ExOpentok.config(:key),
+         token: Token.generate(session["session_id"])
+       }
+     )}
   end
 
+  defp format_response(error), do: error
+
   def init, do: create() |> format_response()
 
+  def init! do
+    case init() do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
+
   @doc """
   Handle location
   """
@@ -120,4 +151,11 @@ defmodule ExOpentok.Session do
     |> Client.http_request()
     |> Client.handle_response()
   end
+
+  def delete!(session_id, connection_id) do
+    case delete(session_id, connection_id) do
+      {:ok, response} -> response
+      {:error, error} -> raise error
+    end
+  end
 end
diff --git a/test/ex_opentok_test.exs b/test/ex_opentok_test.exs
index 5d797ac..cf2ff38 100644
--- a/test/ex_opentok_test.exs
+++ b/test/ex_opentok_test.exs
@@ -4,8 +4,8 @@ defmodule ExOpentokTest do
   alias ExOpentok.{Archive, Client, Exception, Session, Token}
 
   @api_key ExOpentok.config(:key)
-  @session ExOpentok.init()
-  @list ExOpentok.Archive.list()
+  @session ExOpentok.init!()
+  @list ExOpentok.Archive.list!()
 
   # ARCHIVE
 
@@ -21,7 +21,7 @@ defmodule ExOpentokTest do
     first_item = @list["items"] |> Enum.at(0)
 
     first_item["id"]
-    |> Archive.find()
+    |> Archive.find!()
     |> Helper.same_map?(Helper.archive_keys())
   end
 
@@ -31,7 +31,7 @@ defmodule ExOpentokTest do
 
   # Client.http_request()
   test "should get 200 when request get" do
-    response =
+    {:ok, response} =
       Client.http_request(
         "https://api.opentok.com/v2/project/#{@api_key}/archive?offset=0&count=1000",
         :get
@@ -40,16 +40,16 @@ defmodule ExOpentokTest do
     assert response.status == 200
   end
 
-  # Client.handle_response()
+  # Client.handle_response!()
   test "should handle response 200" do
     response = Mock.http_response_archive_list()
-    assert Client.handle_response(response) == Mock.archive_list()
+    assert Client.handle_response!(response) == Mock.archive_list()
   end
 
-  # Client.handle_response()
+  # Client.handle_response!()
   test "should raise if no response 200" do
     assert_raise RuntimeError, fn ->
-      Mock.http_response_error() |> Client.handle_response()
+      Mock.http_response_error() |> Client.handle_response!()
     end
   end
 
diff --git a/test/test_helper.exs b/test/test_helper.exs
index 587b9df..6bbe187 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -34,61 +34,64 @@ end
 
 defmodule ExOpentokTest.Mock do
   def session do
-    %{
-      :api_key => "01234567",
-      :token =>
-        "T1==cGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3NcGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3NcGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3NcGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3N==",
-      "create_dt" => "Tue Apr 11 08:56:40 PDT 2017",
-      "ice_credential_expiration" => 86100,
-      "ice_server" => nil,
-      "ice_servers" => nil,
-      "media_server_hostname" => nil,
-      "media_server_url" => "",
-      "messaging_server_url" => nil,
-      "messaging_url" => nil,
-      "partner_id" => "01234567",
-      "project_id" => "01234567",
-      "properties" => nil,
-      "session_id" => "1_MX40MX40NTgxMMX40NTgxMMX40NTgxMMX40NTgxMMX40NTgxMMX40NTg",
-      "session_status" => nil,
-      "status_invalid" => nil,
-      "symphony_address" => nil
-    }
+    {:ok,
+     %{
+       :api_key => "01234567",
+       :token =>
+         "T1==cGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3NcGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3NcGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3NcGFydG5lcl9pZD00NTgxMTExMiZzaWc9OUVBOTIyQjlFQzM0NUIxNkI3N==",
+       "create_dt" => "Tue Apr 11 08:56:40 PDT 2017",
+       "ice_credential_expiration" => 86100,
+       "ice_server" => nil,
+       "ice_servers" => nil,
+       "media_server_hostname" => nil,
+       "media_server_url" => "",
+       "messaging_server_url" => nil,
+       "messaging_url" => nil,
+       "partner_id" => "01234567",
+       "project_id" => "01234567",
+       "properties" => nil,
+       "session_id" => "1_MX40MX40NTgxMMX40NTgxMMX40NTgxMMX40NTgxMMX40NTgxMMX40NTg",
+       "session_status" => nil,
+       "status_invalid" => nil,
+       "symphony_address" => nil
+     }}
   end
 
   def http_response_archive_list do
-    %{
-      body:
-        "{\"count\":1,\"items\":[{\"id\":\"5c48fb13-f27a-465d-94a7-e581d8ed49f9\",\"status\":\"expired\",\"name\":\"Ruby Archiving Sample App\",\"reason\":\"user initiated\",\"sessionId\":\"1_MX40NTgxMTExMn5-MTQ5MTY4MTU4NzU4Nn5VVU8yY1FsdThVVUU5UUVzd1VkTEh1SDJ-fg\",\"projectId\":45811112,\"createdAt\":1491682306000,\"size\":1742751,\"duration\":21,\"outputMode\":\"composed\",\"hasAudio\":true,\"hasVideo\":true,\"sha256sum\":\"97+WlyjwtOvrrNr2zG8NBTvZgqpSq5PGdgonBOTK7Fw=\",\"password\":\"\",\"updatedAt\":1491943883000,\"url\":null,\"partnerId\":45811112}]}",
-      headers: %{
-        hdrs: %{
-          "connection" => "keep-alive",
-          "content-type" => "application/json",
-          "date" => "Wed, 12 Apr 2017 08:25:59 GMT",
-          "server" => "nginx",
-          "strict-transport-security" => "max-age=31536000; includeSubdomains",
-          "transfer-encoding" => "chunked"
-        }
-      },
-      status: 200
-    }
+    {:ok,
+     %{
+       body:
+         "{\"count\":1,\"items\":[{\"id\":\"5c48fb13-f27a-465d-94a7-e581d8ed49f9\",\"status\":\"expired\",\"name\":\"Ruby Archiving Sample App\",\"reason\":\"user initiated\",\"sessionId\":\"1_MX40NTgxMTExMn5-MTQ5MTY4MTU4NzU4Nn5VVU8yY1FsdThVVUU5UUVzd1VkTEh1SDJ-fg\",\"projectId\":45811112,\"createdAt\":1491682306000,\"size\":1742751,\"duration\":21,\"outputMode\":\"composed\",\"hasAudio\":true,\"hasVideo\":true,\"sha256sum\":\"97+WlyjwtOvrrNr2zG8NBTvZgqpSq5PGdgonBOTK7Fw=\",\"password\":\"\",\"updatedAt\":1491943883000,\"url\":null,\"partnerId\":45811112}]}",
+       headers: %{
+         hdrs: %{
+           "connection" => "keep-alive",
+           "content-type" => "application/json",
+           "date" => "Wed, 12 Apr 2017 08:25:59 GMT",
+           "server" => "nginx",
+           "strict-transport-security" => "max-age=31536000; includeSubdomains",
+           "transfer-encoding" => "chunked"
+         }
+       },
+       status: 200
+     }}
   end
 
   def http_response_error do
-    %{
-      body: "{}",
-      headers: %{
-        hdrs: %{
-          "connection" => "keep-alive",
-          "content-type" => "application/json",
-          "date" => "Wed, 12 Apr 2017 08:25:59 GMT",
-          "server" => "nginx",
-          "strict-transport-security" => "max-age=31536000; includeSubdomains",
-          "transfer-encoding" => "chunked"
-        }
-      },
-      status: 400
-    }
+    {:ok,
+     %{
+       body: "{}",
+       headers: %{
+         hdrs: %{
+           "connection" => "keep-alive",
+           "content-type" => "application/json",
+           "date" => "Wed, 12 Apr 2017 08:25:59 GMT",
+           "server" => "nginx",
+           "strict-transport-security" => "max-age=31536000; includeSubdomains",
+           "transfer-encoding" => "chunked"
+         }
+       },
+       status: 400
+     }}
   end
 
   def archive_list do