diff --git a/alignai/client.py b/alignai/client.py
index 43d93cf..1f9d6c7 100644
--- a/alignai/client.py
+++ b/alignai/client.py
@@ -19,6 +19,12 @@
 from alignai.ingestion.v1alpha.event_pb2 import Event, EventProperties
 from alignai.logger import get_logger
 from alignai.utils import CustomProperties, datetime_to_timestamp, serialize_custom_properties
+from alignai.validate import (
+    ValidationError,
+    validate_custom_properties_or_raise,
+    validate_session_id_or_raise,
+    validate_user_id_or_raise,
+)
 from alignai.worker import Worker
 
 
@@ -76,6 +82,13 @@ def open_session(
             assistant_id (str, optional): Assistant ID. Defaults to "DEFAULT".
             custom_properties (dict[str, str] | None, optional): Custom properties associated with the session. Defaults to None.
         """
+        validate_session_id_or_raise(session_id)
+        validate_user_id_or_raise(user_id)
+        if len(assistant_id) > 64:
+            raise ValidationError("assistant_id must be at most 64 characters")
+        if custom_properties:
+            validate_custom_properties_or_raise(custom_properties)
+
         session_properties_args = {"session_id": session_id, "user_id": user_id, "assistant_id": assistant_id}
         open_session_event = Event(
             id=uuid.uuid4().hex,
@@ -95,6 +108,8 @@ def close_session(self, session_id: str) -> None:
         Args:
             session_id (str): Session ID.
         """
+        validate_session_id_or_raise(session_id)
+
         close_session_event = Event(
             id=uuid.uuid4().hex,
             type=EventTypes.SESSION_CLOSE,
@@ -125,6 +140,16 @@ def identify_user(
             create_time (datetime | None, optional): User creation time. Defaults to None.
             custom_properties (dict[str, str] | None, optional): Custom properties associated with the user. Defaults to None.
         """  # noqa: E501
+        validate_user_id_or_raise(user_id)
+        if display_name and len(display_name) > 64:
+            raise ValidationError("display_name must be at most 64 characters")
+        if email and len(email) > 256:
+            raise ValidationError("email must be at most 256 characters")
+        if country_code and len(country_code) != 2:
+            raise ValidationError("country_code must be ISO Alpha-2 code")
+        if custom_properties:
+            validate_custom_properties_or_raise(custom_properties)
+
         user_properties_args = {"user_id": user_id}
         if display_name is not None:
             user_properties_args["user_display_name"] = display_name
@@ -166,6 +191,14 @@ def create_message(
             content (str): Content of the message.
             custom_properties (dict[str, str] | None, optional): Custom properties associated with the message. Defaults to None.
         """  # noqa: E501
+        validate_session_id_or_raise(session_id)
+        if message_index <= 0:
+            raise ValidationError("message_index must be greater than 0")
+        if not content:
+            raise ValidationError("content is required")
+        if custom_properties:
+            validate_custom_properties_or_raise(custom_properties)
+
         if message_index <= 0:
             self.logger.error(f"Invalid message index '{message_index}': Message index must be a positive integer")
             return
diff --git a/alignai/validate.py b/alignai/validate.py
new file mode 100644
index 0000000..0ff3993
--- /dev/null
+++ b/alignai/validate.py
@@ -0,0 +1,32 @@
+class ValidationError(ValueError):
+    def __init__(self, message: str):
+        self.message = message
+
+    def __str__(self):
+        return f"ValidationError: {self.message}"
+
+
+def validate_session_id_or_raise(session_id: str):
+    if not session_id:
+        raise ValidationError("session_id is required")
+    if len(session_id) > 64:
+        raise ValidationError("session_id must be at most 64 characters")
+
+
+def validate_user_id_or_raise(user_id: str):
+    if not user_id:
+        raise ValidationError("user_id is required")
+    if len(user_id) > 64:
+        raise ValidationError("user_id must be at most 64 characters")
+
+
+def validate_custom_properties_or_raise(custom_properties: dict[str, str]):
+    if len(custom_properties) > 10:
+        raise ValidationError("custom_properties must have at most 10 keys")
+    for key, value in custom_properties.items():
+        if not key:
+            raise ValidationError("key of custom_property is required")
+        if len(key) > 64:
+            raise ValidationError("key of custom_property must be at most 64 characters")
+        if len(value) > 256:
+            raise ValidationError("value of custom_property must be at most 256 characters")