diff --git a/README.md b/README.md
index 9b6de4060d90f8b41e3bea580d53360c2fb62c1b..e37aa8a21136c96703e44b1f9183eb69e2ccf285 100644
--- a/README.md
+++ b/README.md
@@ -44,7 +44,11 @@ cuteDogTool := fantasy.NewAgentTool(
 )
 
 // Equip your agent.
-agent := fantasy.NewAgent(model, fantasy.WithTools(cuteDogTool))
+agent := fantasy.NewAgent(
+  model,
+  fantasy.WithSystemPrompt("You are a moderately helpful, dog-centric assistant."),
+  fantasy.WithTools(cuteDogTool),
+)
 
 // Put that agent to work!
 const prompt = "Find all the cute dogs in Silver Lake, Los Angeles."
diff --git a/examples/simple/main.go b/examples/simple/main.go
index 67ffd64abf486ff4fbc49350ea7ee7ffed6624de..cc6b0f583b9dbaefe9c334138019263a30396445 100644
--- a/examples/simple/main.go
+++ b/examples/simple/main.go
@@ -47,7 +47,10 @@ func main() {
 	cuteDogTool := fantasy.NewAgentTool("cute_dog_tool", "Provide up-to-date info on cute dogs.", fetchCuteDogInfo)
 
 	// Equip your agent.
-	agent := fantasy.NewAgent(model, fantasy.WithTools(cuteDogTool))
+	agent := fantasy.NewAgent(model,
+		fantasy.WithSystemPrompt("You are a moderately helpful, dog-centric assistant."),
+		fantasy.WithTools(cuteDogTool),
+	)
 
 	// Put that agent to work!
 	const prompt = "Find all the cute dogs in Silver Lake, Los Angeles."