diff --git a/paperqa/types.py b/paperqa/types.py
index fd203589..d0255aca 100644
--- a/paperqa/types.py
+++ b/paperqa/types.py
@@ -34,14 +34,21 @@ class LLMResult(BaseModel):
     id: UUID = Field(default_factory=uuid4)
     answer_id: UUID | None = None
     name: str | None = None
-    prompt: str | list[dict] | None = None
+    prompt: str | list[dict] | None = Field(
+        default=None,
+        description="Optional prompt (str) or list of serialized prompts (list[dict]).",
+    )
     text: str = ""
     prompt_count: int = 0
     completion_count: int = 0
     model: str
     date: str
-    seconds_to_first_token: float = 0
-    seconds_to_last_token: float = 0
+    seconds_to_first_token: float = Field(
+        default=0.0, description="Delta time (sec) to first response token's arrival."
+    )
+    seconds_to_last_token: float = Field(
+        default=0.0, description="Delta time (sec) to last response token's arrival."
+    )
 
     def __str__(self):
         return self.text