From d5d90686afc227e9785f44536fc20006fccf2c5b Mon Sep 17 00:00:00 2001
From: Mark Ericksen <brainlid@gmail.com>
Date: Thu, 21 Nov 2024 16:58:25 -0700
Subject: [PATCH] improved error handling - handle Antrhropic "overload_error"
 - return {:error, %LangChainError{}} instead of a {:error, String.t()} -
 updated lots of chat models and chains - LLMChain.run returns an error struct
 - LangChainError.type is a string code that is easier to detect and have
 coded handling for more scenarios

---
 lib/chains/data_extraction_chain.ex       |  7 +-
 lib/chains/llm_chain.ex                   | 30 +++++--
 lib/chains/routing_chain.ex               |  2 +-
 lib/chains/text_to_title_chain.ex         |  2 +-
 lib/chat_models/chat_anthropic.ex         | 90 +++++++++++++--------
 lib/chat_models/chat_bumblebee.ex         | 14 ++--
 lib/chat_models/chat_google_ai.ex         | 57 ++++++++------
 lib/chat_models/chat_mistral_ai.ex        | 40 ++++++----
 lib/chat_models/chat_model.ex             |  3 +-
 lib/chat_models/chat_ollama_ai.ex         | 26 +++---
 lib/chat_models/chat_open_ai.ex           | 49 ++++++------
 lib/chat_models/chat_vertex_ai.ex         | 45 ++++++-----
 lib/langchain_error.ex                    | 21 ++++-
 lib/message.ex                            |  5 +-
 lib/utils/chain_result.ex                 | 29 ++++---
 test/chains/llm_chain_test.exs            | 30 ++++---
 test/chat_models/chat_anthropic_test.exs  | 67 +++++++++++++---
 test/chat_models/chat_google_ai_test.exs  | 19 +++--
 test/chat_models/chat_mistral_ai_test.exs | 25 ++++--
 test/chat_models/chat_open_ai_test.exs    | 96 ++++++++++++++---------
 test/chat_models/chat_vertex_ai_test.exs  | 16 ++--
 test/langchain_error_test.exs             | 18 +++++
 test/utils/chain_result_test.exs          | 28 +++++--
 23 files changed, 473 insertions(+), 246 deletions(-)
 create mode 100644 test/langchain_error_test.exs

diff --git a/lib/chains/data_extraction_chain.ex b/lib/chains/data_extraction_chain.ex
index db9e4688..56b2d05c 100644
--- a/lib/chains/data_extraction_chain.ex
+++ b/lib/chains/data_extraction_chain.ex
@@ -73,6 +73,7 @@ defmodule LangChain.Chains.DataExtractionChain do
   alias LangChain.PromptTemplate
   alias LangChain.Message
   alias LangChain.Message.ToolCall
+  alias LangChain.LangChainError
   alias LangChain.Chains.LLMChain
   alias LangChain.ChatModels.ChatOpenAI
 
@@ -86,7 +87,7 @@ Passage:
   Run the data extraction chain.
   """
   @spec run(ChatOpenAI.t(), json_schema :: map(), prompt :: [any()], opts :: Keyword.t()) ::
-          {:ok, result :: [any()]} | {:error, String.t()}
+          {:ok, result :: [any()]} | {:error, LangChainError.t()}
   def run(llm, json_schema, prompt, opts \\ []) do
     verbose = Keyword.get(opts, :verbose, false)
 
@@ -123,7 +124,7 @@ Passage:
           {:ok, info}
 
         other ->
-          {:error, "Unexpected response. #{inspect(other)}"}
+          {:error, LangChainError.exception("Unexpected response. #{inspect(other)}")}
       end
     rescue
       exception ->
@@ -131,7 +132,7 @@ Passage:
           "Caught unexpected exception in DataExtractionChain. Error: #{inspect(exception)}"
         )
 
-        {:error, "Unexpected error in DataExtractionChain. Check logs for details."}
+        {:error, LangChainError.exception("Unexpected error in DataExtractionChain. Check logs for details.")}
     end
   end
 
diff --git a/lib/chains/llm_chain.ex b/lib/chains/llm_chain.ex
index 18fca41c..b1bb5169 100644
--- a/lib/chains/llm_chain.ex
+++ b/lib/chains/llm_chain.ex
@@ -236,7 +236,7 @@ defmodule LangChain.Chains.LLMChain do
     an opportunity to use the `ToolResult` information in an assistant response
     message. In essence, this mode always gives the LLM the last word.
   """
-  @spec run(t(), Keyword.t()) :: {:ok, t()} | {:error, t(), String.t()}
+  @spec run(t(), Keyword.t()) :: {:ok, t()} | {:error, t(), LangChainError.t()}
   def run(chain, opts \\ [])
 
   def run(%LLMChain{} = chain, opts) do
@@ -275,12 +275,16 @@ defmodule LangChain.Chains.LLMChain do
   # Repeatedly run the chain until we get a successful ToolResponse or processed
   # assistant message. Once we've reached success, it is not submitted back to the LLM,
   # the process ends there.
-  @spec run_until_success(t()) :: {:ok, t()} | {:error, t(), String.t()}
+  @spec run_until_success(t()) :: {:ok, t()} | {:error, t(), LangChainError.t()}
   defp run_until_success(%LLMChain{last_message: %Message{} = last_message} = chain) do
     stop_or_recurse =
       cond do
         chain.current_failure_count >= chain.max_retry_count ->
-          {:error, chain, "Exceeded max failure count"}
+          {:error, chain,
+           LangChainError.exception(
+             type: "exceeded_failure_count",
+             message: "Exceeded max failure count"
+           )}
 
         last_message.role == :tool && !Message.tool_had_errors?(last_message) ->
           # a successful tool result has no errors
@@ -318,7 +322,7 @@ defmodule LangChain.Chains.LLMChain do
   # Repeatedly run the chain while `needs_response` is true. This will execute
   # tools and re-submit the tool result to the LLM giving the LLM an
   # opportunity to execute more tools or return a response.
-  @spec run_while_needs_response(t()) :: {:ok, t()} | {:error, t(), String.t()}
+  @spec run_while_needs_response(t()) :: {:ok, t()} | {:error, t(), LangChainError.t()}
   defp run_while_needs_response(%LLMChain{needs_response: false} = chain) do
     {:ok, chain}
   end
@@ -337,11 +341,16 @@ defmodule LangChain.Chains.LLMChain do
   end
 
   # internal reusable function for running the chain
-  @spec do_run(t()) :: {:ok, t()} | {:error, t(), String.t()}
+  @spec do_run(t()) :: {:ok, t()} | {:error, t(), LangChainError.t()}
   defp do_run(%LLMChain{current_failure_count: current_count, max_retry_count: max} = chain)
        when current_count >= max do
     Callbacks.fire(chain.callbacks, :on_retries_exceeded, [chain])
-    {:error, chain, "Exceeded max failure count"}
+
+    {:error, chain,
+     LangChainError.exception(
+       type: "exceeded_failure_count",
+       message: "Exceeded max failure count"
+     )}
   end
 
   defp do_run(%LLMChain{} = chain) do
@@ -385,10 +394,15 @@ defmodule LangChain.Chains.LLMChain do
 
         {:ok, updated_chain}
 
-      {:error, reason} ->
+      {:error, %LangChainError{} = reason} ->
         if chain.verbose, do: IO.inspect(reason, label: "ERROR")
         Logger.error("Error during chat call. Reason: #{inspect(reason)}")
         {:error, chain, reason}
+
+      {:error, string_reason} when is_binary(string_reason) ->
+        if chain.verbose, do: IO.inspect(string_reason, label: "ERROR")
+        Logger.error("Error during chat call. Reason: #{inspect(string_reason)}")
+        {:error, chain, LangChainError.exception(message: string_reason)}
     end
   end
 
@@ -736,7 +750,7 @@ defmodule LangChain.Chains.LLMChain do
 
       case Function.execute(function, call.arguments, context) do
         {:ok, llm_result, processed_result} ->
-          if verbose, do: IO.inspect(llm_result, label: "FUNCTION RESULT")
+          if verbose, do: IO.inspect(processed_result, label: "FUNCTION PROCESSED RESULT")
           # successful execution and storage of processed_content.
           ToolResult.new!(%{
             tool_call_id: call.call_id,
diff --git a/lib/chains/routing_chain.ex b/lib/chains/routing_chain.ex
index a4364f36..4b97abb7 100644
--- a/lib/chains/routing_chain.ex
+++ b/lib/chains/routing_chain.ex
@@ -106,7 +106,7 @@ defmodule LangChain.Chains.RoutingChain do
   route.
   """
   @spec run(t(), Keyword.t()) ::
-          {:ok, LLMChain.t(), Message.t() | [Message.t()]} | {:error, String.t()}
+          {:ok, LLMChain.t(), Message.t() | [Message.t()]} | {:error, LangChainError.t()}
   def run(%RoutingChain{} = chain, opts \\ []) do
     default_name = chain.default_route.name
 
diff --git a/lib/chains/text_to_title_chain.ex b/lib/chains/text_to_title_chain.ex
index 4857a905..1a14c26f 100644
--- a/lib/chains/text_to_title_chain.ex
+++ b/lib/chains/text_to_title_chain.ex
@@ -124,7 +124,7 @@ defmodule LangChain.Chains.TextToTitleChain do
       |> TextToTitleChain.run()
 
   """
-  @spec run(t(), Keyword.t()) :: {:ok, LLMChain.t()} | {:error, LLMChain.t(), String.t()}
+  @spec run(t(), Keyword.t()) :: {:ok, LLMChain.t()} | {:error, LLMChain.t(), LangChainError.t()}
   def run(%TextToTitleChain{} = chain, opts \\ []) do
     messages =
       [
diff --git a/lib/chat_models/chat_anthropic.ex b/lib/chat_models/chat_anthropic.ex
index 56866ef5..4d800bc2 100644
--- a/lib/chat_models/chat_anthropic.ex
+++ b/lib/chat_models/chat_anthropic.ex
@@ -237,15 +237,18 @@ defmodule LangChain.ChatModels.ChatAnthropic do
     |> Map.drop([:model, :stream])
   end
 
-  defp get_tool_choice(%ChatAnthropic{tool_choice: %{"type" => "tool", "name" => name}=_tool_choice}) when is_binary(name) and byte_size(name) > 0,
-    do: %{"type" => "tool", "name" => name}
+  defp get_tool_choice(%ChatAnthropic{
+         tool_choice: %{"type" => "tool", "name" => name} = _tool_choice
+       })
+       when is_binary(name) and byte_size(name) > 0,
+       do: %{"type" => "tool", "name" => name}
 
-  defp get_tool_choice(%ChatAnthropic{tool_choice: %{"type" => type}=_tool_choice}) when is_binary(type) and byte_size(type) > 0,
-    do: %{"type" => type}
+  defp get_tool_choice(%ChatAnthropic{tool_choice: %{"type" => type} = _tool_choice})
+       when is_binary(type) and byte_size(type) > 0,
+       do: %{"type" => type}
 
   defp get_tool_choice(%ChatAnthropic{}), do: nil
 
-
   defp get_tools_for_api(nil), do: []
 
   defp get_tools_for_api(tools) do
@@ -288,15 +291,15 @@ defmodule LangChain.ChatModels.ChatAnthropic do
     try do
       # make base api request and perform high-level success/failure checks
       case do_api_request(anthropic, messages, functions) do
-        {:error, reason} ->
-          {:error, reason}
+        {:error, %LangChainError{} = error} ->
+          {:error, error}
 
         parsed_data ->
           {:ok, parsed_data}
       end
     rescue
       err in LangChainError ->
-        {:error, err.message}
+        {:error, err}
     end
   end
 
@@ -305,18 +308,20 @@ defmodule LangChain.ChatModels.ChatAnthropic do
   # The result of the function is:
   #
   # - `result` - where `result` is a data-structure like a list or map.
-  # - `{:error, reason}` - Where reason is a string explanation of what went wrong.
+  # - `{:error, %LangChainError{} = reason}` - An `LangChain.LangChainError` exception with an explanation of what went wrong.
   #
   # If `stream: false`, the completed message is returned.
   #
   # Retries the request up to 3 times on transient errors with a 1 second delay
   @doc false
   @spec do_api_request(t(), [Message.t()], ChatModel.tools(), (any() -> any())) ::
-          list() | struct() | {:error, String.t()}
+          list() | struct() | {:error, LangChainError.t()}
   def do_api_request(anthropic, messages, tools, retry_count \\ 3)
 
   def do_api_request(_anthropic, _messages, _functions, 0) do
-    raise LangChainError, "Retries exceeded. Connection failed."
+    raise LangChainError,
+      type: "retries_exceeded",
+      message: "Retries exceeded. Connection failed."
   end
 
   def do_api_request(
@@ -341,7 +346,7 @@ defmodule LangChain.ChatModels.ChatAnthropic do
     |> Req.post()
     # parse the body and return it as parsed structs
     |> case do
-      {:ok, %Req.Response{body: data} = response} ->
+      {:ok, %Req.Response{status: 200, body: data} = response} ->
         Callbacks.fire(anthropic.callbacks, :on_llm_ratelimit_info, [
           anthropic,
           get_ratelimit_info(response.headers)
@@ -361,8 +366,12 @@ defmodule LangChain.ChatModels.ChatAnthropic do
             result
         end
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:ok, %Req.Response{status: 529}} ->
+        {:error, LangChainError.exception(type: "overloaded", message: "Overloaded")}
+
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       {:error, %Req.TransportError{reason: :closed}} ->
         # Force a retry by making a recursive call decrementing the counter
@@ -370,8 +379,9 @@ defmodule LangChain.ChatModels.ChatAnthropic do
         do_api_request(anthropic, messages, tools, retry_count - 1)
 
       other ->
-        Logger.error("Unexpected and unhandled API response! #{inspect(other)}")
-        other
+        message = "Unexpected and unhandled API response! #{inspect(other)}"
+        Logger.error(message)
+        {:error, LangChainError.exception(type: "unexpected_response", message: message)}
     end
   end
 
@@ -405,11 +415,11 @@ defmodule LangChain.ChatModels.ChatAnthropic do
 
         data
 
-      {:error, %LangChainError{message: reason}} ->
-        {:error, reason}
+      {:error, %LangChainError{} = error} ->
+        {:error, error}
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error, LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       {:error, %Req.TransportError{reason: :closed}} ->
         # Force a retry by making a recursive call decrementing the counter
@@ -417,11 +427,9 @@ defmodule LangChain.ChatModels.ChatAnthropic do
         do_api_request(anthropic, messages, tools, retry_count - 1)
 
       other ->
-        Logger.error(
-          "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
-        )
-
-        {:error, "Unexpected response"}
+        message = "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
+        Logger.error(message)
+        {:error, LangChainError.exception(type: "unexpected_response", message: message)}
     end
   end
 
@@ -466,7 +474,7 @@ defmodule LangChain.ChatModels.ChatAnthropic do
           | [Message.t()]
           | MessageDelta.t()
           | [MessageDelta.t()]
-          | {:error, String.t()}
+          | {:error, LangChainError.t()}
   def do_process_response(_model, %{
         "role" => "assistant",
         "content" => contents,
@@ -572,30 +580,43 @@ defmodule LangChain.ChatModels.ChatAnthropic do
     |> to_response()
   end
 
-  def do_process_response(_model, %{"error" => %{"message" => reason}}) do
+  def do_process_response(_model, %{
+        "type" => "error",
+        "error" => %{"type" => type, "message" => reason}
+      }) do
     Logger.error("Received error from API: #{inspect(reason)}")
-    {:error, reason}
+    {:error, LangChainError.exception(type: type, message: reason)}
+  end
+
+  def do_process_response(_model, %{"error" => %{"message" => reason} = error}) do
+    Logger.error("Received error from API: #{inspect(reason)}")
+    {:error, LangChainError.exception(type: error["type"], message: reason)}
   end
 
   def do_process_response(_model, {:error, %Jason.DecodeError{} = response}) do
     error_message = "Received invalid JSON: #{inspect(response)}"
     Logger.error(error_message)
-    {:error, error_message}
+
+    {:error,
+     LangChainError.exception(type: "invalid_json", message: error_message, original: response)}
   end
 
   def do_process_response(%ChatAnthropic{bedrock: %BedrockConfig{}}, %{"message" => message}) do
-    {:error, "Received error from API: #{message}"}
+    {:error, LangChainError.exception(message: "Received error from API: #{message}")}
   end
 
   def do_process_response(%ChatAnthropic{bedrock: %BedrockConfig{}}, %{
         bedrock_exception: exceptions
       }) do
-    {:error, "Stream exception received: #{inspect(exceptions)}"}
+    {:error,
+     LangChainError.exception(message: "Stream exception received: #{inspect(exceptions)}")}
   end
 
   def do_process_response(_model, other) do
     Logger.error("Trying to process an unexpected response. #{inspect(other)}")
-    {:error, "Unexpected response"}
+
+    {:error,
+     LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
   end
 
   # for parsing a list of received content JSON objects
@@ -650,7 +671,9 @@ defmodule LangChain.ChatModels.ChatAnthropic do
   end
 
   defp to_response({:ok, message}), do: message
-  defp to_response({:error, changeset}), do: {:error, Utils.changeset_error_to_string(changeset)}
+
+  defp to_response({:error, %Ecto.Changeset{} = changeset}),
+    do: {:error, LangChainError.exception(changeset)}
 
   defp stop_reason_to_status("end_turn"), do: :complete
   defp stop_reason_to_status("tool_use"), do: :complete
@@ -711,6 +734,7 @@ defmodule LangChain.ChatModels.ChatAnthropic do
   defp relevant_event?("event: content_block_delta\n" <> _rest), do: true
   defp relevant_event?("event: content_block_start\n" <> _rest), do: true
   defp relevant_event?("event: message_delta\n" <> _rest), do: true
+  defp relevant_event?("event: error\n" <> _rest), do: true
   # ignoring
   defp relevant_event?("event: message_start\n" <> _rest), do: false
   defp relevant_event?("event: ping\n" <> _rest), do: false
diff --git a/lib/chat_models/chat_bumblebee.ex b/lib/chat_models/chat_bumblebee.ex
index 569bbb53..2d0fc346 100644
--- a/lib/chat_models/chat_bumblebee.ex
+++ b/lib/chat_models/chat_bumblebee.ex
@@ -179,8 +179,8 @@ defmodule LangChain.ChatModels.ChatBumblebee do
       {:ok, chain} ->
         chain
 
-      {:error, changeset} ->
-        raise LangChainError, changeset
+      {:error, %Ecto.Changeset{} = changeset} ->
+        raise LangChainError.exception(changeset)
     end
   end
 
@@ -229,7 +229,7 @@ defmodule LangChain.ChatModels.ChatBumblebee do
       end
     rescue
       err in LangChainError ->
-        {:error, err.message}
+        {:error, err}
     end
   end
 
@@ -259,10 +259,10 @@ defmodule LangChain.ChatModels.ChatBumblebee do
         # return a list of the complete message. As a list for compatibility.
         [message]
 
-      {:error, changeset} ->
+      {:error, %Ecto.Changeset{} = changeset} ->
         reason = Utils.changeset_error_to_string(changeset)
         Logger.error("Failed to create non-streamed full message: #{inspect(reason)}")
-        {:error, reason}
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -296,14 +296,14 @@ defmodule LangChain.ChatModels.ChatBumblebee do
             Callbacks.fire(model.callbacks, :on_llm_new_delta, [model, delta])
             delta
 
-          {:error, changeset} ->
+          {:error, %Ecto.Changeset{} = changeset} ->
             reason = Utils.changeset_error_to_string(changeset)
 
             Logger.error(
               "Failed to process received model's MessageDelta data: #{inspect(reason)}"
             )
 
-            raise LangChainError, reason
+            raise LangChainError.exception(changeset)
         end
     end
 
diff --git a/lib/chat_models/chat_google_ai.ex b/lib/chat_models/chat_google_ai.ex
index 3adb0d23..43b47a4d 100644
--- a/lib/chat_models/chat_google_ai.ex
+++ b/lib/chat_models/chat_google_ai.ex
@@ -319,7 +319,7 @@ defmodule LangChain.ChatModels.ChatGoogleAI do
 
   @doc false
   @spec do_api_request(t(), [Message.t()], [Function.t()]) ::
-          list() | struct() | {:error, String.t()}
+          list() | struct() | {:error, LangChainError.t()}
   def do_api_request(%ChatGoogleAI{stream: false} = google_ai, messages, tools) do
     req =
       Req.new(
@@ -344,11 +344,16 @@ defmodule LangChain.ChatModels.ChatGoogleAI do
             result
         end
 
-      {:ok, %Req.Response{status: status}} ->
-        {:error, "Failed with status: #{inspect(status)}"}
+      {:ok, %Req.Response{status: status} = err} ->
+        {:error,
+         LangChainError.exception(
+           message: "Failed with status: #{inspect(status)}",
+           original: err
+         )}
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       other ->
         Logger.error("Unexpected and unhandled API response! #{inspect(other)}")
@@ -378,21 +383,27 @@ defmodule LangChain.ChatModels.ChatGoogleAI do
         # this behavior by forcing the final delta to have `status: :complete`.
         complete_final_delta(data)
 
-      {:ok, %Req.Response{status: status}} ->
-        {:error, "Failed with status: #{inspect(status)}"}
+      {:ok, %Req.Response{status: status} = err} ->
+        {:error,
+         LangChainError.exception(
+           message: "Failed with status: #{inspect(status)}",
+           original: err
+         )}
 
-      {:error, %LangChainError{message: reason}} ->
-        {:error, reason}
+      {:error, %LangChainError{} = error} ->
+        {:error, error}
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       other ->
         Logger.error(
           "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
         )
 
-        {:error, "Unexpected response"}
+        {:error,
+         LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
     end
   end
 
@@ -478,8 +489,8 @@ defmodule LangChain.ChatModels.ChatGoogleAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -517,8 +528,8 @@ defmodule LangChain.ChatModels.ChatGoogleAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -539,8 +550,8 @@ defmodule LangChain.ChatModels.ChatGoogleAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -574,25 +585,25 @@ defmodule LangChain.ChatModels.ChatGoogleAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
   def do_process_response(_model, %{"error" => %{"message" => reason}}, _) do
     Logger.error("Received error from API: #{inspect(reason)}")
-    {:error, reason}
+    {:error, LangChainError.exception(message: reason)}
   end
 
   def do_process_response(_model, {:error, %Jason.DecodeError{} = response}, _) do
     error_message = "Received invalid JSON: #{inspect(response)}"
     Logger.error(error_message)
-    {:error, error_message}
+    {:error, LangChainError.exception(type: "invalid_json", message: error_message, original: response)}
   end
 
   def do_process_response(_model, other, _) do
     Logger.error("Trying to process an unexpected response. #{inspect(other)}")
-    {:error, "Unexpected response"}
+    {:error, LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
   end
 
   @doc false
diff --git a/lib/chat_models/chat_mistral_ai.ex b/lib/chat_models/chat_mistral_ai.ex
index 802f6b05..4cab112e 100644
--- a/lib/chat_models/chat_mistral_ai.ex
+++ b/lib/chat_models/chat_mistral_ai.ex
@@ -156,7 +156,7 @@ defmodule LangChain.ChatModels.ChatMistralAI do
       end
     rescue
       err in LangChainError ->
-        {:error, err.message}
+        {:error, err}
     end
   end
 
@@ -165,7 +165,10 @@ defmodule LangChain.ChatModels.ChatMistralAI do
   def do_api_request(mistral, messages, functions, retry_count \\ 3)
 
   def do_api_request(_mistral, _messages, _functions, 0) do
-    raise LangChainError, "Retries exceeded. Connection failed."
+    raise LangChainError.exception(
+            type: "retries_exceeded",
+            message: "Retries exceeded. Connection failed."
+          )
   end
 
   def do_api_request(
@@ -199,8 +202,9 @@ defmodule LangChain.ChatModels.ChatMistralAI do
             result
         end
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       {:error, %Req.TransportError{reason: :closed}} ->
         # Force a retry by making a recursive call decrementing the counter
@@ -237,11 +241,12 @@ defmodule LangChain.ChatModels.ChatMistralAI do
       {:ok, %Req.Response{body: data}} ->
         data
 
-      {:error, %LangChainError{message: reason}} ->
-        {:error, reason}
+      {:error, %LangChainError{} = err} ->
+        {:error, err}
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       {:error, %Req.TransportError{reason: :closed}} ->
         # Force a retry by making a recursive call decrementing the counter
@@ -253,7 +258,8 @@ defmodule LangChain.ChatModels.ChatMistralAI do
           "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
         )
 
-        {:error, "Unexpected response"}
+        {:error,
+         LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
     end
   end
 
@@ -264,7 +270,7 @@ defmodule LangChain.ChatModels.ChatMistralAI do
           | [Message.t()]
           | MessageDelta.t()
           | [MessageDelta.t()]
-          | {:error, String.t()}
+          | {:error, LangChainError.t()}
   def do_process_response(model, %{"choices" => choices}) when is_list(choices) do
     # process each response individually. Return a list of all processed choices
     for choice <- choices do
@@ -344,25 +350,29 @@ defmodule LangChain.ChatModels.ChatMistralAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
   def do_process_response(_model, %{"error" => %{"message" => reason}}) do
     Logger.error("Received error from API: #{inspect(reason)}")
-    {:error, reason}
+    {:error, LangChainError.exception(message: reason)}
   end
 
   def do_process_response(_model, {:error, %Jason.DecodeError{} = response}) do
     error_message = "Received invalid JSON: #{inspect(response)}"
     Logger.error(error_message)
-    {:error, error_message}
+
+    {:error,
+     LangChainError.exception(type: "invalid_json", message: error_message, original: response)}
   end
 
   def do_process_response(_model, other) do
     Logger.error("Trying to process an unexpected response. #{inspect(other)}")
-    {:error, "Unexpected response"}
+
+    {:error,
+     LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
   end
 
   @doc """
diff --git a/lib/chat_models/chat_model.ex b/lib/chat_models/chat_model.ex
index 145fc276..72187407 100644
--- a/lib/chat_models/chat_model.ex
+++ b/lib/chat_models/chat_model.ex
@@ -3,10 +3,11 @@ defmodule LangChain.ChatModels.ChatModel do
   alias LangChain.Message
   alias LangChain.MessageDelta
   alias LangChain.Function
+  alias LangChain.LangChainError
   alias LangChain.Utils
 
   @type call_response ::
-          {:ok, Message.t() | [Message.t()] | [MessageDelta.t()]} | {:error, String.t()}
+          {:ok, Message.t() | [Message.t()] | [MessageDelta.t()]} | {:error, LangChainError.t()}
 
   @type tool :: Function.t()
   @type tools :: [tool()]
diff --git a/lib/chat_models/chat_ollama_ai.ex b/lib/chat_models/chat_ollama_ai.ex
index d42326a5..c79d9c7a 100644
--- a/lib/chat_models/chat_ollama_ai.ex
+++ b/lib/chat_models/chat_ollama_ai.ex
@@ -265,10 +265,10 @@ defmodule LangChain.ChatModels.ChatOllamaAI do
   # The result of the function is:
   #
   # - `result` - where `result` is a data-structure like a list or map.
-  # - `{:error, reason}` - Where reason is a string explanation of what went wrong.
+  # - `{:error, reason}` - Where reason is a `LangChain.LangChainError`
+  #   explanation of what went wrong.
   #
-  # **NOTE:** callback function are IGNORED for ollama ai
-  # When `stream: true` is
+  # **NOTE:** callback function are IGNORED for ollama ai When `stream: true` is
   # If `stream: false`, the completed message is returned.
   #
   # If `stream: true`, the completed message is returned after MessageDelta's.
@@ -276,11 +276,11 @@ defmodule LangChain.ChatModels.ChatOllamaAI do
   # Retries the request up to 3 times on transient errors with a 1 second delay
   @doc false
   @spec do_api_request(t(), [Message.t()], [Function.t()]) ::
-          list() | struct() | {:error, String.t()}
+          list() | struct() | {:error, LangChainError.t()}
   def do_api_request(ollama_ai, messages, functions, retry_count \\ 3)
 
   def do_api_request(_ollama_ai, _messages, _functions, 0) do
-    raise LangChainError, "Retries exceeded. Connection failed."
+    raise LangChainError.exception(type: "retries_exceeded", message: "Retries exceeded. Connection failed.")
   end
 
   def do_api_request(
@@ -348,11 +348,11 @@ defmodule LangChain.ChatModels.ChatOllamaAI do
       {:ok, %Req.Response{body: data}} ->
         data
 
-      {:error, %LangChainError{message: reason}} ->
-        {:error, reason}
+      {:error, %LangChainError{} = error} ->
+        {:error, error}
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error, LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       {:error, %Req.TransportError{reason: :closed}} ->
         # Force a retry by making a recursive call decrementing the counter
@@ -364,7 +364,7 @@ defmodule LangChain.ChatModels.ChatOllamaAI do
           "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
         )
 
-        {:error, "Unexpected response"}
+        {:error, LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
     end
   end
 
@@ -382,7 +382,7 @@ defmodule LangChain.ChatModels.ChatOllamaAI do
 
   def do_process_response(_model, %{"error" => reason}) do
     Logger.error("Received error from API: #{inspect(reason)}")
-    {:error, reason}
+    {:error, LangChainError.exception(message: reason)}
   end
 
   defp create_message(message, status, message_type) do
@@ -390,8 +390,8 @@ defmodule LangChain.ChatModels.ChatOllamaAI do
       {:ok, new_message} ->
         new_message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
diff --git a/lib/chat_models/chat_open_ai.ex b/lib/chat_models/chat_open_ai.ex
index c2f0cfbc..9fec7bbe 100644
--- a/lib/chat_models/chat_open_ai.ex
+++ b/lib/chat_models/chat_open_ai.ex
@@ -493,7 +493,7 @@ defmodule LangChain.ChatModels.ChatOpenAI do
       end
     rescue
       err in LangChainError ->
-        {:error, err.message}
+        {:error, err}
     end
   end
 
@@ -517,7 +517,7 @@ defmodule LangChain.ChatModels.ChatOpenAI do
   # Retries the request up to 3 times on transient errors with a 1 second delay
   @doc false
   @spec do_api_request(t(), [Message.t()], ChatModel.tools(), integer()) ::
-          list() | struct() | {:error, String.t()}
+          list() | struct() | {:error, LangChainError.t()}
   def do_api_request(openai, messages, tools, retry_count \\ 3)
 
   def do_api_request(_openai, _messages, _tools, 0) do
@@ -564,7 +564,7 @@ defmodule LangChain.ChatModels.ChatOpenAI do
         ])
 
         case do_process_response(openai, data) do
-          {:error, reason} ->
+          {:error, %LangChainError{} = reason} ->
             {:error, reason}
 
           result ->
@@ -572,8 +572,9 @@ defmodule LangChain.ChatModels.ChatOpenAI do
             result
         end
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       {:error, %Req.TransportError{reason: :closed}} ->
         # Force a retry by making a recursive call decrementing the counter
@@ -617,11 +618,12 @@ defmodule LangChain.ChatModels.ChatOpenAI do
 
         data
 
-      {:error, %LangChainError{message: reason}} ->
-        {:error, reason}
+      {:error, %LangChainError{} = error} ->
+        {:error, error}
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       {:error, %Req.TransportError{reason: :closed}} ->
         # Force a retry by making a recursive call decrementing the counter
@@ -633,7 +635,8 @@ defmodule LangChain.ChatModels.ChatOpenAI do
           "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
         )
 
-        {:error, "Unexpected response"}
+        {:error,
+         LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
     end
   end
 
@@ -751,8 +754,8 @@ defmodule LangChain.ChatModels.ChatOpenAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -792,8 +795,8 @@ defmodule LangChain.ChatModels.ChatOpenAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -811,10 +814,10 @@ defmodule LangChain.ChatModels.ChatOpenAI do
       {:ok, %ToolCall{} = call} ->
         call
 
-      {:error, changeset} ->
+      {:error, %Ecto.Changeset{} = changeset} ->
         reason = Utils.changeset_error_to_string(changeset)
         Logger.error("Failed to process ToolCall for a function. Reason: #{reason}")
-        {:error, reason}
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -838,10 +841,10 @@ defmodule LangChain.ChatModels.ChatOpenAI do
       {:ok, %ToolCall{} = call} ->
         call
 
-      {:error, changeset} ->
+      {:error, %Ecto.Changeset{} = changeset} ->
         reason = Utils.changeset_error_to_string(changeset)
         Logger.error("Failed to process ToolCall for a function. Reason: #{reason}")
-        {:error, reason}
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -856,25 +859,25 @@ defmodule LangChain.ChatModels.ChatOpenAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
   def do_process_response(_model, %{"error" => %{"message" => reason}}) do
     Logger.error("Received error from API: #{inspect(reason)}")
-    {:error, reason}
+    {:error, LangChainError.exception(message: reason)}
   end
 
   def do_process_response(_model, {:error, %Jason.DecodeError{} = response}) do
     error_message = "Received invalid JSON: #{inspect(response)}"
     Logger.error(error_message)
-    {:error, error_message}
+    {:error, LangChainError.exception(type: "invalid_json", message: error_message, original: response)}
   end
 
   def do_process_response(_model, other) do
     Logger.error("Trying to process an unexpected response. #{inspect(other)}")
-    {:error, "Unexpected response"}
+    {:error, LangChainError.exception(message: "Unexpected response")}
   end
 
   defp finish_reason_to_status(nil), do: :incomplete
diff --git a/lib/chat_models/chat_vertex_ai.ex b/lib/chat_models/chat_vertex_ai.ex
index 460f81a2..90cfb9ed 100644
--- a/lib/chat_models/chat_vertex_ai.ex
+++ b/lib/chat_models/chat_vertex_ai.ex
@@ -289,13 +289,13 @@ defmodule LangChain.ChatModels.ChatVertexAI do
       end
     rescue
       err in LangChainError ->
-        {:error, err.message}
+        {:error, err}
     end
   end
 
   @doc false
   @spec do_api_request(t(), [Message.t()], [Function.t()]) ::
-          list() | struct() | {:error, String.t()}
+          list() | struct() | {:error, LangChainError.t()}
   def do_api_request(%ChatVertexAI{stream: false} = vertex_ai, messages, tools) do
     req =
       Req.new(
@@ -321,8 +321,9 @@ defmodule LangChain.ChatModels.ChatVertexAI do
             result
         end
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       other ->
         Logger.error("Unexpected and unhandled API response! #{inspect(other)}")
@@ -353,18 +354,20 @@ defmodule LangChain.ChatModels.ChatVertexAI do
         # this behavior by forcing the final delta to have `status: :complete`.
         complete_final_delta(data)
 
-      {:error, %LangChainError{message: reason}} ->
-        {:error, reason}
+      {:error, %LangChainError{} = error} ->
+        {:error, error}
 
-      {:error, %Req.TransportError{reason: :timeout}} ->
-        {:error, "Request timed out"}
+      {:error, %Req.TransportError{reason: :timeout} = err} ->
+        {:error,
+         LangChainError.exception(type: "timeout", message: "Request timed out", original: err)}
 
       other ->
         Logger.error(
           "Unhandled and unexpected response from streamed post call. #{inspect(other)}"
         )
 
-        {:error, "Unexpected response"}
+        {:error,
+         LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
     end
   end
 
@@ -428,8 +431,8 @@ defmodule LangChain.ChatModels.ChatVertexAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -468,8 +471,8 @@ defmodule LangChain.ChatModels.ChatVertexAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -486,8 +489,8 @@ defmodule LangChain.ChatModels.ChatVertexAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -530,8 +533,8 @@ defmodule LangChain.ChatModels.ChatVertexAI do
       {:ok, message} ->
         message
 
-      {:error, changeset} ->
-        {:error, Utils.changeset_error_to_string(changeset)}
+      {:error, %Ecto.Changeset{} = changeset} ->
+        {:error, LangChainError.exception(changeset)}
     end
   end
 
@@ -543,12 +546,16 @@ defmodule LangChain.ChatModels.ChatVertexAI do
   def do_process_response({:error, %Jason.DecodeError{} = response}, _) do
     error_message = "Received invalid JSON: #{inspect(response)}"
     Logger.error(error_message)
-    {:error, error_message}
+
+    {:error,
+     LangChainError.exception(type: "invalid_json", message: error_message, original: response)}
   end
 
   def do_process_response(other, _) do
     Logger.error("Trying to process an unexpected response. #{inspect(other)}")
-    {:error, "Unexpected response"}
+
+    {:error,
+     LangChainError.exception(type: "unexpected_response", message: "Unexpected response")}
   end
 
   @doc false
diff --git a/lib/langchain_error.ex b/lib/langchain_error.ex
index a3385d72..c192313e 100644
--- a/lib/langchain_error.ex
+++ b/lib/langchain_error.ex
@@ -9,13 +9,22 @@ defmodule LangChain.LangChainError do
 
       raise LangChainError, "Message text"
 
+      raise LangChainError, type: "overloaded_error", message: "Message text"
+
+  The error struct contains the following keys:
+
+  - `:type` - A string code to make detecting and responding to specific errors easier. This may have values like "length" or "overloaded_error". The specific meaning of the type is dependent on the service or model.
+
+  - `:message` - A string representation or explanation of the error.
+
+  - `:original` - If a exception was caught and wrapped into a LangChainError, this may be the original message that was encountered.
   """
   import LangChain.Utils, only: [changeset_error_to_string: 1]
   alias __MODULE__
 
   @type t :: %LangChainError{}
 
-  defexception [:message]
+  defexception [:type, :message, :original]
 
   @doc """
   Create the exception using either a message or a changeset who's errors are
@@ -28,6 +37,14 @@ defmodule LangChain.LangChainError do
 
   def exception(%Ecto.Changeset{} = changeset) do
     text_reason = changeset_error_to_string(changeset)
-    %LangChainError{message: text_reason}
+    %LangChainError{type: "changeset", message: text_reason}
+  end
+
+  def exception(opts) when is_list(opts) do
+    %LangChainError{
+      message: Keyword.fetch!(opts, :message),
+      type: Keyword.get(opts, :type),
+      original: Keyword.get(opts, :original),
+    }
   end
 end
diff --git a/lib/message.ex b/lib/message.ex
index ddfcceee..f4452c53 100644
--- a/lib/message.ex
+++ b/lib/message.ex
@@ -241,7 +241,10 @@ defmodule LangChain.Message do
                 # convert the error to text and return error tuple
                 {:error, Utils.changeset_error_to_string(changeset)}
 
-              {:error, reason} ->
+              {:error, %LangChainError{message: message}} ->
+                {:error, message}
+
+              {:error, reason} when is_binary(reason) ->
                 {:error, reason}
             end
           end)
diff --git a/lib/utils/chain_result.ex b/lib/utils/chain_result.ex
index ddf67991..c2ace2e8 100644
--- a/lib/utils/chain_result.ex
+++ b/lib/utils/chain_result.ex
@@ -21,10 +21,10 @@ defmodule LangChain.Utils.ChainResult do
   @spec to_string(
           LLMChain.t()
           | {:ok, LLMChain.t()}
-          | {:error, LLMChain.t(), String.t()}
+          | {:error, LLMChain.t(), LangChainError.t()}
         ) ::
-          {:ok, String.t()} | {:error, LLMChain.t(), String.t()}
-  def to_string({:error, chain, reason}) when is_binary(reason) do
+          {:ok, String.t()} | {:error, LLMChain.t(), LangChainError.t()}
+  def to_string({:error, chain, %LangChainError{} = reason}) do
     # if an error was passed in, forward it through.
     {:error, chain, reason}
   end
@@ -34,7 +34,15 @@ defmodule LangChain.Utils.ChainResult do
   end
 
   # when received a single ContentPart
-  def to_string(%LLMChain{last_message: %Message{role: :assistant, status: :complete, content: [%ContentPart{type: :text} = part]}} = _chain) do
+  def to_string(
+        %LLMChain{
+          last_message: %Message{
+            role: :assistant,
+            status: :complete,
+            content: [%ContentPart{type: :text} = part]
+          }
+        } = _chain
+      ) do
     {:ok, part.content}
   end
 
@@ -43,15 +51,16 @@ defmodule LangChain.Utils.ChainResult do
   end
 
   def to_string(%LLMChain{last_message: %Message{role: :assistant, status: _incomplete}} = chain) do
-    {:error, chain, "Message is incomplete"}
+    {:error, chain, LangChainError.exception(type: "to_string", message: "Message is incomplete")}
   end
 
   def to_string(%LLMChain{last_message: %Message{}} = chain) do
-    {:error, chain, "Message is not from assistant"}
+    {:error, chain,
+     LangChainError.exception(type: "to_string", message: "Message is not from assistant")}
   end
 
   def to_string(%LLMChain{last_message: nil} = chain) do
-    {:error, chain, "No last message"}
+    {:error, chain, LangChainError.exception(type: "to_string", message: "No last message")}
   end
 
   @doc """
@@ -64,7 +73,7 @@ defmodule LangChain.Utils.ChainResult do
   def to_string!(%LLMChain{} = chain) do
     case ChainResult.to_string(chain) do
       {:ok, result} -> result
-      {:error, _chain, reason} -> raise LangChainError, reason
+      {:error, _chain, %LangChainError{} = exception} -> raise exception
     end
   end
 
@@ -92,8 +101,8 @@ defmodule LangChain.Utils.ChainResult do
       {:ok, updated} ->
         updated
 
-      {:error, _chain, reason} ->
-        raise LangChainError, reason
+      {:error, _chain, %LangChainError{} = exception} ->
+        raise exception
     end
   end
 end
diff --git a/test/chains/llm_chain_test.exs b/test/chains/llm_chain_test.exs
index ee957fd8..63b6269a 100644
--- a/test/chains/llm_chain_test.exs
+++ b/test/chains/llm_chain_test.exs
@@ -948,28 +948,30 @@ defmodule LangChain.Chains.LLMChainTest do
     @tag live_call: true, live_open_ai: true
     test "NON-STREAMING handles receiving an error when no messages sent" do
       # create and run the chain
-      {:error, _updated_chain, reason} =
+      {:error, _updated_chain, %LangChainError{} = reason} =
         LLMChain.new!(%{
           llm: ChatOpenAI.new!(%{seed: 0, stream: false}),
           verbose: false
         })
         |> LLMChain.run()
 
-      assert reason ==
+      assert reason.type == nil
+      assert reason.message ==
                "Invalid 'messages': empty array. Expected an array with minimum length 1, but got an empty array instead."
     end
 
     @tag live_call: true, live_open_ai: true
     test "STREAMING handles receiving an error when no messages sent" do
       # create and run the chain
-      {:error, _updated_chain, reason} =
+      {:error, _updated_chain, %LangChainError{} = reason} =
         LLMChain.new!(%{
           llm: ChatOpenAI.new!(%{seed: 0, stream: true}),
           verbose: false
         })
         |> LLMChain.run()
 
-      assert reason ==
+      assert reason.type == nil
+      assert reason.message ==
                "Invalid 'messages': empty array. Expected an array with minimum length 1, but got an empty array instead."
     end
 
@@ -1061,13 +1063,14 @@ defmodule LangChain.Chains.LLMChainTest do
 
       # errors when trying to send a PromptTemplate
       # create and run the chain
-      {:error, _updated_chain, reason} =
+      {:error, _updated_chain, %LangChainError{} = reason} =
         %{llm: ChatOpenAI.new!(%{seed: 0})}
         |> LLMChain.new!()
         |> LLMChain.add_messages(messages)
         |> LLMChain.run()
 
-      assert reason =~ ~r/PromptTemplates must be/
+      assert reason.type == nil
+      assert reason.message =~ ~r/PromptTemplates must be/
     end
 
     test "mode: :while_needs_response - increments current_failure_count on parse failure", %{
@@ -1087,7 +1090,7 @@ defmodule LangChain.Chains.LLMChainTest do
         Message.new_user!("Say what I want you to say.")
       ]
 
-      {:error, error_chain, reason} =
+      {:error, error_chain, %LangChainError{} = reason} =
         chain
         |> LLMChain.message_processors([JsonProcessor.new!()])
         |> LLMChain.add_messages(messages)
@@ -1095,7 +1098,8 @@ defmodule LangChain.Chains.LLMChainTest do
         |> LLMChain.run(mode: :while_needs_response)
 
       assert error_chain.current_failure_count == 3
-      assert reason == "Exceeded max failure count"
+      assert reason.type == "exceeded_failure_count"
+      assert reason.message == "Exceeded max failure count"
 
       [m1, m2, m3, m4, m5, m6, m7] = error_chain.messages
 
@@ -1155,7 +1159,7 @@ defmodule LangChain.Chains.LLMChainTest do
           callbacks: [handler]
         })
 
-      {:error, error_chain, reason} =
+      {:error, error_chain, %LangChainError{} = reason} =
         chain
         |> LLMChain.message_processors([JsonProcessor.new!()])
         |> LLMChain.add_messages([
@@ -1165,7 +1169,8 @@ defmodule LangChain.Chains.LLMChainTest do
         |> LLMChain.run(mode: :while_needs_response)
 
       assert error_chain.current_failure_count == 2
-      assert reason == "Exceeded max failure count"
+      assert reason.type == "exceeded_failure_count"
+      assert reason.message == "Exceeded max failure count"
 
       [m1, m2, m3, m4, m5] = error_chain.messages
 
@@ -1368,7 +1373,7 @@ defmodule LangChain.Chains.LLMChainTest do
         {:ok, fake_messages}
       end)
 
-      {:error, updated_chain, reason} =
+      {:error, updated_chain, %LangChainError{} = reason} =
         %{llm: ChatOpenAI.new!(%{stream: false}), verbose: false}
         |> LLMChain.new!()
         |> LLMChain.add_tools([fail_func])
@@ -1376,7 +1381,8 @@ defmodule LangChain.Chains.LLMChainTest do
         |> LLMChain.add_message(Message.new_user!("Execute the fail_func tool."))
         |> LLMChain.run(mode: :until_success)
 
-      assert reason == "Exceeded max failure count"
+      assert reason.type == "exceeded_failure_count"
+      assert reason.message == "Exceeded max failure count"
       assert updated_chain.current_failure_count == 3
     end
   end
diff --git a/test/chat_models/chat_anthropic_test.exs b/test/chat_models/chat_anthropic_test.exs
index 9afe43ac..9022b17f 100644
--- a/test/chat_models/chat_anthropic_test.exs
+++ b/test/chat_models/chat_anthropic_test.exs
@@ -14,6 +14,7 @@ defmodule LangChain.ChatModels.ChatAnthropicTest do
   alias LangChain.Function
   alias LangChain.FunctionParam
   alias LangChain.BedrockHelpers
+  alias LangChain.LangChainError
 
   @test_model "claude-3-opus-20240229"
   @bedrock_test_model "anthropic.claude-3-5-sonnet-20240620-v1:0"
@@ -287,16 +288,24 @@ defmodule LangChain.ChatModels.ChatAnthropicTest do
 
     test "handles error messages", %{model: model} do
       error = "Invalid API key"
+      message = "Received error from API: #{error}"
 
-      assert {:error, "Received error from API: #{error}"} ==
+      assert {:error, exception} =
                ChatAnthropic.do_process_response(model, %{"message" => error})
+
+      assert exception.type == nil
+      assert exception.message == message
     end
 
     test "handles stream error messages", %{model: model} do
       error = "Internal error"
+      message = "Stream exception received: #{inspect(error)}"
 
-      assert {:error, "Stream exception received: #{inspect(error)}"} ==
+      assert {:error, exception} =
                ChatAnthropic.do_process_response(model, %{bedrock_exception: error})
+
+      assert exception.type == nil
+      assert exception.message == message
     end
   end
 
@@ -495,6 +504,22 @@ defmodule LangChain.ChatModels.ChatAnthropicTest do
       assert call.name == "get_weather"
       assert call.arguments == %{"location" => "San Francisco, CA", "unit" => "celsius"}
     end
+
+    test "handles receiving overloaded error", %{model: model} do
+      response = %{
+        "type" => "error",
+        "error" => %{
+          "details" => nil,
+          "type" => "overloaded_error",
+          "message" => "Overloaded"
+        }
+      }
+
+      assert {:error, exception} = ChatAnthropic.do_process_response(model, response)
+
+      assert exception.type == "overloaded_error"
+      assert exception.message == "Overloaded"
+    end
   end
 
   describe "call/2" do
@@ -502,12 +527,12 @@ defmodule LangChain.ChatModels.ChatAnthropicTest do
     test "handles when invalid API key given" do
       {:ok, chat} = ChatAnthropic.new(%{stream: true, api_key: "invalid"})
 
-      {:error, reason} =
+      {:error, %LangChainError{} = exception} =
         ChatAnthropic.call(chat, [
           Message.new_user!("Return the response 'Colorful Threads'.")
         ])
 
-      assert reason == "Authentication failure with request"
+      assert exception.message == "Authentication failure with request"
     end
 
     @tag live_call: true, live_anthropic_bedrock: true
@@ -521,12 +546,12 @@ defmodule LangChain.ChatModels.ChatAnthropicTest do
           }
         })
 
-      {:error, reason} =
+      {:error, %LangChainError{} = exception} =
         ChatAnthropic.call(chat, [
           Message.new_user!("Return the response 'Colorful Threads'.")
         ])
 
-      assert reason ==
+      assert exception.message ==
                "Received error from API: The security token included in the request is invalid."
     end
 
@@ -567,13 +592,7 @@ defmodule LangChain.ChatModels.ChatAnthropicTest do
                    role: :assistant
                  },
                  %LangChain.MessageDelta{
-                   content: " up the good work",
-                   status: :incomplete,
-                   index: nil,
-                   role: :assistant
-                 },
-                 %LangChain.MessageDelta{
-                   content: "!",
+                   content: " up the good work!",
                    status: :incomplete,
                    index: nil,
                    role: :assistant
@@ -860,6 +879,28 @@ data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text
 
       assert buffer == ""
     end
+
+    test "handles error overloaded message" do
+      chunk = """
+      event: error\ndata: {\"type\":\"error\",\"error\":{\"details\":null,\"type\":\"overloaded_error\",\"message\":\"Overloaded\"}}
+
+      """
+
+      {parsed, buffer} = ChatAnthropic.decode_stream(%ChatAnthropic{}, {chunk, ""})
+
+      assert [
+               %{
+                 "type" => "error",
+                 "error" => %{
+                   "details" => nil,
+                   "type" => "overloaded_error",
+                   "message" => "Overloaded"
+                 }
+               }
+             ] = parsed
+
+      assert buffer == ""
+    end
   end
 
   describe "for_api/1" do
diff --git a/test/chat_models/chat_google_ai_test.exs b/test/chat_models/chat_google_ai_test.exs
index 4eee94e7..7e882f39 100644
--- a/test/chat_models/chat_google_ai_test.exs
+++ b/test/chat_models/chat_google_ai_test.exs
@@ -402,8 +402,9 @@ defmodule ChatModels.ChatGoogleAITest do
         ]
       }
 
-      assert [{:error, error_string}] = ChatGoogleAI.do_process_response(model, response)
-      assert error_string == "role: is invalid"
+      assert [{:error, %LangChainError{} = error}] = ChatGoogleAI.do_process_response(model, response)
+      assert error.type == "changeset"
+      assert error.message == "role: is invalid"
     end
 
     test "handles receiving function calls", %{model: model} do
@@ -482,20 +483,24 @@ defmodule ChatModels.ChatGoogleAITest do
         }
       }
 
-      assert {:error, error_string} = ChatGoogleAI.do_process_response(model, response)
-      assert error_string == "Invalid request"
+      assert {:error, %LangChainError{} = error} = ChatGoogleAI.do_process_response(model, response)
+      assert error.type == nil
+      assert error.message == "Invalid request"
     end
 
     test "handles Jason.DecodeError", %{model: model} do
       response = {:error, %Jason.DecodeError{}}
 
-      assert {:error, error_string} = ChatGoogleAI.do_process_response(model, response)
-      assert "Received invalid JSON:" <> _ = error_string
+      assert {:error, %LangChainError{} = error} = ChatGoogleAI.do_process_response(model, response)
+      assert error.type == "invalid_json"
+      assert "Received invalid JSON:" <> _ = error.message
     end
 
     test "handles unexpected response with error", %{model: model} do
       response = %{}
-      assert {:error, "Unexpected response"} = ChatGoogleAI.do_process_response(model, response)
+      assert {:error, %LangChainError{} = error} = ChatGoogleAI.do_process_response(model, response)
+      assert error.type == "unexpected_response"
+      assert error.message == "Unexpected response"
     end
   end
 
diff --git a/test/chat_models/chat_mistral_ai_test.exs b/test/chat_models/chat_mistral_ai_test.exs
index ce0483c7..deb24c89 100644
--- a/test/chat_models/chat_mistral_ai_test.exs
+++ b/test/chat_models/chat_mistral_ai_test.exs
@@ -4,6 +4,7 @@ defmodule LangChain.ChatModels.ChatMistralAITest do
   alias LangChain.ChatModels.ChatMistralAI
   alias LangChain.Message
   alias LangChain.MessageDelta
+  alias LangChain.LangChainError
 
   setup do
     model = ChatMistralAI.new!(%{"model" => "mistral-tiny"})
@@ -125,7 +126,10 @@ defmodule LangChain.ChatModels.ChatMistralAITest do
         ]
       }
 
-      assert [{:error, "role: is invalid"}] = ChatMistralAI.do_process_response(model, response)
+      assert [{:error, %LangChainError{} = error}] =
+               ChatMistralAI.do_process_response(model, response)
+
+      assert error.message == "role: is invalid"
     end
 
     test "handles receiving MessageDeltas as well", %{model: model} do
@@ -159,20 +163,29 @@ defmodule LangChain.ChatModels.ChatMistralAITest do
         }
       }
 
-      assert {:error, error_string} = ChatMistralAI.do_process_response(model, response)
-      assert error_string == "Invalid request"
+      assert {:error, %LangChainError{} = error} = ChatMistralAI.do_process_response(model, response)
+
+      assert error.type == nil
+      assert error.message == "Invalid request"
     end
 
     test "handles Jason.DecodeError", %{model: model} do
       response = {:error, %Jason.DecodeError{}}
 
-      assert {:error, error_string} = ChatMistralAI.do_process_response(model, response)
-      assert "Received invalid JSON:" <> _ = error_string
+      assert {:error, %LangChainError{} = error} = ChatMistralAI.do_process_response(model, response)
+
+      assert error.type == "invalid_json"
+      assert "Received invalid JSON:" <> _ = error.message
     end
 
     test "handles unexpected response with error", %{model: model} do
       response = %{}
-      assert {:error, "Unexpected response"} = ChatMistralAI.do_process_response(model, response)
+
+      assert {:error, %LangChainError{} = error} =
+               ChatMistralAI.do_process_response(model, response)
+
+      assert error.type == "unexpected_response"
+      assert error.message == "Unexpected response"
     end
   end
 
diff --git a/test/chat_models/chat_open_ai_test.exs b/test/chat_models/chat_open_ai_test.exs
index ba40f6f2..acd5a22f 100644
--- a/test/chat_models/chat_open_ai_test.exs
+++ b/test/chat_models/chat_open_ai_test.exs
@@ -7,6 +7,7 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
   alias LangChain.Function
   alias LangChain.FunctionParam
   alias LangChain.TokenUsage
+  alias LangChain.LangChainError
   alias LangChain.Message
   alias LangChain.Message.ContentPart
   alias LangChain.Message.ToolCall
@@ -83,11 +84,12 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
         }
       }
 
-      {:ok, openai} = ChatOpenAI.new(%{
-        "model" => @test_model,
-        "json_response" => true,
-        "json_schema" => json_schema
-      })
+      {:ok, openai} =
+        ChatOpenAI.new(%{
+          "model" => @test_model,
+          "json_response" => true,
+          "json_schema" => json_schema
+        })
 
       assert openai.json_response == true
       assert openai.json_schema == json_schema
@@ -149,10 +151,11 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
       assert data.model == @test_model
       assert data.temperature == 1
       assert data.frequency_penalty == 0.5
+
       assert data.response_format == %{
-        "type" => "json_schema",
-        "json_schema" => json_schema
-      }
+               "type" => "json_schema",
+               "json_schema" => json_schema
+             }
     end
 
     test "generates a map for an API call with max_tokens set" do
@@ -490,7 +493,7 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
             "description" => nil,
             "enum" => ["yellow", "red", "green"],
             "type" => "string"
-        }
+          }
         },
         "required" => ["p1"]
       }
@@ -910,8 +913,9 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
       {:ok, chat} =
         ChatOpenAI.new(%{model: "gpt-4-0613", seed: 0, stream: false, temperature: 1})
 
-      {:error, reason} = ChatOpenAI.call(chat, [too_large_user_request()])
-      assert reason =~ "maximum context length"
+      {:error, %LangChainError{} = reason} = ChatOpenAI.call(chat, [too_large_user_request()])
+      assert reason.type == nil
+      assert reason.message =~ "maximum context length"
     end
   end
 
@@ -1066,8 +1070,11 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
         }
       }
 
-      assert {:error, reason} = ChatOpenAI.do_process_response(model, response)
-      assert reason == "tool_calls: arguments: invalid json"
+      assert {:error, %LangChainError{} = reason} =
+               ChatOpenAI.do_process_response(model, response)
+
+      assert reason.type == "changeset"
+      assert reason.message == "tool_calls: arguments: invalid json"
     end
 
     test "handles a single tool_call from list", %{model: model} do
@@ -1098,9 +1105,10 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
         "type" => "function"
       }
 
-      assert {:error, message} = ChatOpenAI.do_process_response(model, call)
+      assert {:error, %LangChainError{} = error} = ChatOpenAI.do_process_response(model, call)
 
-      assert message == "arguments: invalid json"
+      assert error.type == "changeset"
+      assert error.message == "arguments: invalid json"
     end
 
     test "handles streamed deltas for multiple tool calls", %{model: model} do
@@ -1210,13 +1218,19 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
     end
 
     test "handles json parse error from server", %{model: model} do
-      {:error, "Received invalid JSON: " <> _} =
+      {:error, %LangChainError{} = error} =
         ChatOpenAI.do_process_response(model, Jason.decode("invalid json"))
+
+      assert error.type == "invalid_json"
+      assert "Received invalid JSON: " <> _ = error.message
     end
 
     test "handles unexpected response", %{model: model} do
-      {:error, "Unexpected response"} =
+      {:error, %LangChainError{} = error} =
         ChatOpenAI.do_process_response(model, "unexpected")
+
+      assert error.type == nil
+      assert error.message == "Unexpected response"
     end
 
     test "return multiple responses when given multiple choices", %{model: model} do
@@ -1274,9 +1288,10 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
     test "STREAMING handles receiving an error when no messages sent" do
       chat = ChatOpenAI.new!(%{seed: 0, stream: true})
 
-      {:error, reason} = ChatOpenAI.call(chat, [], [])
+      {:error, %LangChainError{} = reason} = ChatOpenAI.call(chat, [], [])
 
-      assert reason ==
+      assert reason.type == nil
+      assert reason.message ==
                "Invalid 'messages': empty array. Expected an array with minimum length 1, but got an empty array instead."
     end
 
@@ -1291,10 +1306,11 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
       {:ok, chat} =
         ChatOpenAI.new(%{seed: 0, stream: true, receive_timeout: 50, callbacks: [handler]})
 
-      {:error, reason} =
+      {:error, %LangChainError{} = reason} =
         ChatOpenAI.call(chat, [Message.new_user!("Why is the sky blue?")], [])
 
-      assert reason == "Request timed out"
+      assert reason.type == "timeout"
+      assert reason.message == "Request timed out"
     end
   end
 
@@ -2018,20 +2034,24 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
 
   describe "set_response_format/1" do
     test "generates a map for an API call with text format when json_response is false" do
-      {:ok, openai} = ChatOpenAI.new(%{
-        model: @test_model,
-        json_response: false
-      })
+      {:ok, openai} =
+        ChatOpenAI.new(%{
+          model: @test_model,
+          json_response: false
+        })
+
       data = ChatOpenAI.for_api(openai, [], [])
 
       assert data.response_format == %{"type" => "text"}
     end
 
     test "generates a map for an API call with json_object format when json_response is true and no schema" do
-      {:ok, openai} = ChatOpenAI.new(%{
-        model: @test_model,
-        json_response: true
-      })
+      {:ok, openai} =
+        ChatOpenAI.new(%{
+          model: @test_model,
+          json_response: true
+        })
+
       data = ChatOpenAI.for_api(openai, [], [])
 
       assert data.response_format == %{"type" => "json_object"}
@@ -2046,17 +2066,19 @@ defmodule LangChain.ChatModels.ChatOpenAITest do
         }
       }
 
-      {:ok, openai} = ChatOpenAI.new(%{
-        model: @test_model,
-        json_response: true,
-        json_schema: json_schema
-      })
+      {:ok, openai} =
+        ChatOpenAI.new(%{
+          model: @test_model,
+          json_response: true,
+          json_schema: json_schema
+        })
+
       data = ChatOpenAI.for_api(openai, [], [])
 
       assert data.response_format == %{
-        "type" => "json_schema",
-        "json_schema" => json_schema
-      }
+               "type" => "json_schema",
+               "json_schema" => json_schema
+             }
     end
   end
 end
diff --git a/test/chat_models/chat_vertex_ai_test.exs b/test/chat_models/chat_vertex_ai_test.exs
index 1157a1c5..4c6bf6f6 100644
--- a/test/chat_models/chat_vertex_ai_test.exs
+++ b/test/chat_models/chat_vertex_ai_test.exs
@@ -10,6 +10,7 @@ defmodule ChatModels.ChatVertexAITest do
   alias LangChain.Message.ToolResult
   alias LangChain.MessageDelta
   alias LangChain.Function
+  alias LangChain.LangChainError
 
   setup do
     {:ok, hello_world} =
@@ -189,8 +190,9 @@ defmodule ChatModels.ChatVertexAITest do
         ]
       }
 
-      assert [{:error, error_string}] = ChatVertexAI.do_process_response(response)
-      assert error_string == "role: is invalid"
+      assert [{:error, %LangChainError{} = error}] = ChatVertexAI.do_process_response(response)
+      assert error.type == "changeset"
+      assert error.message == "role: is invalid"
     end
 
     test "handles receiving function calls" do
@@ -254,13 +256,17 @@ defmodule ChatModels.ChatVertexAITest do
     test "handles Jason.DecodeError" do
       response = {:error, %Jason.DecodeError{}}
 
-      assert {:error, error_string} = ChatVertexAI.do_process_response(response)
-      assert "Received invalid JSON:" <> _ = error_string
+      assert {:error, %LangChainError{} = error} = ChatVertexAI.do_process_response(response)
+
+      assert error.type == "invalid_json"
+      assert "Received invalid JSON:" <> _ = error.message
     end
 
     test "handles unexpected response with error" do
       response = %{}
-      assert {:error, "Unexpected response"} = ChatVertexAI.do_process_response(response)
+      assert {:error, %LangChainError{} = error} = ChatVertexAI.do_process_response(response)
+      assert error.type == "unexpected_response"
+      assert error.message == "Unexpected response"
     end
   end
 
diff --git a/test/langchain_error_test.exs b/test/langchain_error_test.exs
new file mode 100644
index 00000000..1df2a5aa
--- /dev/null
+++ b/test/langchain_error_test.exs
@@ -0,0 +1,18 @@
+defmodule LangChain.LangChainErrorTest do
+  use ExUnit.Case
+  doctest LangChain.LangChainError
+
+  alias LangChain.LangChainError
+
+  describe "exception/1" do
+    test "supports creating with keyword list" do
+      original = RuntimeError.exception("testing")
+
+      error = LangChainError.exception(type: "test", message: "A test error", original: original)
+
+      assert error.type == "test"
+      assert error.message == "A test error"
+      assert error.original == original
+    end
+  end
+end
diff --git a/test/utils/chain_result_test.exs b/test/utils/chain_result_test.exs
index 2b3a7136..7c363dbf 100644
--- a/test/utils/chain_result_test.exs
+++ b/test/utils/chain_result_test.exs
@@ -11,8 +11,10 @@ defmodule LangChain.Utils.ChainResultTest do
 
   describe "to_string/1" do
     test "passes an error tuple through" do
-      assert {:error, %LLMChain{}, "original error"} ==
-               ChainResult.to_string({:error, %LLMChain{}, "original error"})
+      an_error = LangChainError.exception("original error")
+
+      assert {:error, %LLMChain{}, an_error} ==
+               ChainResult.to_string({:error, %LLMChain{}, an_error})
     end
 
     test "returns {:ok, answer} when valid" do
@@ -30,7 +32,10 @@ defmodule LangChain.Utils.ChainResultTest do
 
     test "returns error when no last message" do
       chain = %LLMChain{last_message: nil}
-      assert {:error, chain, "No last message"} == ChainResult.to_string(chain)
+      assert {:error, _chain, %LangChainError{} = error} = ChainResult.to_string(chain)
+
+      assert error.type == "to_string"
+      assert error.message == "No last message"
     end
 
     test "returns error when incomplete last message" do
@@ -38,7 +43,10 @@ defmodule LangChain.Utils.ChainResultTest do
         last_message: Message.new!(%{role: :assistant, content: "Incomplete", status: :length})
       }
 
-      assert {:error, chain, "Message is incomplete"} == ChainResult.to_string(chain)
+      assert {:error, _chain, %LangChainError{} = error} = ChainResult.to_string(chain)
+
+      assert error.type == "to_string"
+      assert error.message == "Message is incomplete"
     end
 
     test "returns error when last message is not from assistant" do
@@ -46,7 +54,10 @@ defmodule LangChain.Utils.ChainResultTest do
         last_message: Message.new_user!("The question")
       }
 
-      assert {:error, chain, "Message is not from assistant"} == ChainResult.to_string(chain)
+      assert {:error, _chain, %LangChainError{} = error} = ChainResult.to_string(chain)
+
+      assert error.type == "to_string"
+      assert error.message == "Message is not from assistant"
     end
 
     test "handles an LLMChain.run/2 success result" do
@@ -82,7 +93,12 @@ defmodule LangChain.Utils.ChainResultTest do
     test "returns error tuple with reason when invalid" do
       data = %{thing: "one"}
       chain = %LLMChain{last_message: nil}
-      assert {:error, _chain, "No last message"} = ChainResult.to_map(chain, data, :answer)
+
+      assert {:error, _chain, %LangChainError{} = error} =
+               ChainResult.to_map(chain, data, :answer)
+
+      assert error.type == "to_string"
+      assert error.message == "No last message"
     end
   end