diff --git a/app/schemas/api.py b/app/schemas/api.py
index 42c0c0c..b87ddef 100644
--- a/app/schemas/api.py
+++ b/app/schemas/api.py
@@ -1,7 +1,7 @@
 import datetime
 import uuid
 from collections.abc import Iterable
-from typing import Any, Self
+from typing import Annotated, Any, Self
 
 import pydantic
 from pydantic import BaseModel, PositiveInt
@@ -9,6 +9,9 @@
 from app.database import tables
 
 
+MessageText = Annotated[str, pydantic.Field(min_length=1, max_length=4000)]
+
+
 class Base(BaseModel):
     model_config = pydantic.ConfigDict(from_attributes=True)
 
@@ -66,11 +69,11 @@ class ChatDetail(Chat):
 
 class SendMessageRequest(Base):
     idempotency_key: uuid.UUID
-    text: str = pydantic.Field(min_length=1, max_length=4000)
+    text: MessageText
 
 
 class EditMessageRequest(Base):
-    text: str = pydantic.Field(min_length=1, max_length=4000)
+    text: MessageText
 
 
 class Message(Base):
diff --git a/tests/test_schemas.py b/tests/test_schemas.py
index cfb6b81..67c2a82 100644
--- a/tests/test_schemas.py
+++ b/tests/test_schemas.py
@@ -1,4 +1,9 @@
-from app.schemas.api import Collection, User
+import uuid
+
+import pydantic
+import pytest
+
+from app.schemas.api import Collection, EditMessageRequest, SendMessageRequest, User
 from tests.factories import UserFactory
 
 
@@ -6,3 +11,26 @@ def test_collection_builds_from_models() -> None:
     user = UserFactory.build(id=1, username="alice", display_name="Alice")
     collection = Collection[User].from_models([user])
     assert collection.items == [User(id=1, username="alice", display_name="Alice")]
+
+
+def _build_message_request(
+    model: type[SendMessageRequest | EditMessageRequest], text: str
+) -> SendMessageRequest | EditMessageRequest:
+    if model is SendMessageRequest:
+        return SendMessageRequest(idempotency_key=uuid.uuid4(), text=text)
+    return EditMessageRequest(text=text)
+
+
+@pytest.mark.parametrize("model", [SendMessageRequest, EditMessageRequest])
+@pytest.mark.parametrize("text", ["", "x" * 4001], ids=["empty", "over_max"])
+def test_message_request_rejects_out_of_bounds_text(
+    model: type[SendMessageRequest | EditMessageRequest], text: str
+) -> None:
+    with pytest.raises(pydantic.ValidationError):
+        _build_message_request(model, text)
+
+
+@pytest.mark.parametrize("model", [SendMessageRequest, EditMessageRequest])
+def test_message_request_accepts_max_length_text(model: type[SendMessageRequest | EditMessageRequest]) -> None:
+    text = "x" * 4000
+    assert _build_message_request(model, text).text == text