diff --git a/src/schema/schema.py b/src/schema/schema.py
index f6c7206..c9fb8c0 100644
--- a/src/schema/schema.py
+++ b/src/schema/schema.py
@@ -9,6 +9,9 @@
     message_to_dict,
     messages_from_dict,
 )
+from langchain_core.messages import (
+    ChatMessage as LangchainChatMessage,
+)
 from pydantic import BaseModel, Field
 
 
@@ -56,9 +59,9 @@ class StreamInput(UserInput):
 class ChatMessage(BaseModel):
     """Message in a chat."""
 
-    type: Literal["human", "ai", "tool"] = Field(
+    type: Literal["human", "ai", "tool", "custom"] = Field(
         description="Role of the message.",
-        examples=["human", "ai", "tool"],
+        examples=["human", "ai", "tool", "custom"],
     )
     content: str = Field(
         description="Content of the message.",
@@ -82,6 +85,10 @@ class ChatMessage(BaseModel):
         description="Original LangChain message in serialized form.",
         default={},
     )
+    custom_data: dict[str, Any] = Field(
+        description="Custom message data.",
+        default={},
+    )
 
     @classmethod
     def from_langchain(cls, message: BaseMessage) -> "ChatMessage":
@@ -112,9 +119,28 @@ def from_langchain(cls, message: BaseMessage) -> "ChatMessage":
                     original=original,
                 )
                 return tool_message
+            case LangchainChatMessage():
+                if message.role == "custom":
+                    custom_message = cls(
+                        type="custom",
+                        content="",
+                        custom_data=message.content[0],
+                        original=original,
+                    )
+                    return custom_message
+                else:
+                    raise ValueError(f"Unsupported chat message role: {message.role}")
             case _:
                 raise ValueError(f"Unsupported message type: {message.__class__.__name__}")
 
+    @classmethod
+    def from_custom_data(cls, data: dict[str, Any]) -> "ChatMessage":
+        return cls(
+            type="custom",
+            content="",
+            custom_data=data,
+        )
+
     def to_langchain(self) -> BaseMessage:
         """Convert the ChatMessage to a LangChain message."""
         if self.original:
@@ -124,6 +150,11 @@ def to_langchain(self) -> BaseMessage:
         match self.type:
             case "human":
                 return HumanMessage(content=self.content)
+            case "custom":
+                return LangchainChatMessage(
+                    content=[self.custom_data],
+                    role="custom",
+                )
             case _:
                 raise NotImplementedError(f"Unsupported message type: {self.type}")