diff --git a/src/ipython_shell/transport.py b/src/ipython_shell/transport.py
new file mode 100644
index 0000000..f069d95
--- /dev/null
+++ b/src/ipython_shell/transport.py
@@ -0,0 +1,20 @@
+from dataclasses import dataclass
+
+
+@dataclass
+class KernelMessage:
+    """A decoded Jupyter message kept at the transport boundary."""
+
+    msg_type: str
+    parent_id: str | None
+    content: dict[str, object]
+    buffers: list[bytes]
+
+
+@dataclass
+class InputRequest:
+    """A request for user input emitted by a running kernel call."""
+
+    call_id: str
+    prompt: str
+    password: bool
diff --git a/tests/test_transport.py b/tests/test_transport.py
new file mode 100644
index 0000000..8c4b7f7
--- /dev/null
+++ b/tests/test_transport.py
@@ -0,0 +1,21 @@
+import unittest
+
+from ipython_shell.transport import KernelMessage
+
+
+class TransportTests(unittest.TestCase):
+    def test_kernel_message_keeps_content_and_buffers(self):
+        message = KernelMessage(
+            msg_type="display_data",
+            parent_id="call-1",
+            content={"data": {"text/plain": "42"}},
+            buffers=[b"binary"],
+        )
+
+        self.assertEqual(message.parent_id, "call-1")
+        self.assertEqual(message.content["data"], {"text/plain": "42"})
+        self.assertEqual(message.buffers, [b"binary"])
+
+
+if __name__ == "__main__":
+    unittest.main()