diff --git a/stagehand/main.py b/stagehand/main.py
index 45ee8c2..4f8b7c7 100644
--- a/stagehand/main.py
+++ b/stagehand/main.py
@@ -160,6 +160,17 @@ def __init__(
 
         # Handle non-config parameters
         self.api_url = self.config.api_url
+        if not self.api_url:
+            raise ValueError(
+                "api_url is not set. Please set StagehandConfig.api_url "
+                "or the STAGEHAND_API_URL environment variable."
+            )
+
+        if not self.api_url.startswith(("http://", "https://")):
+            raise ValueError(
+                f"Invalid api_url: {self.api_url}. Must start with http:// or https://"
+            )
+
         self.model_api_key = self.config.model_api_key or os.getenv("MODEL_API_KEY")
         self.model_name = self.config.model_name