diff --git a/src/celeste/constraints.py b/src/celeste/constraints.py
index 31befbb..eb5b3da 100644
--- a/src/celeste/constraints.py
+++ b/src/celeste/constraints.py
@@ -382,8 +382,11 @@ def __call__(self, value: list) -> list:
         """Validate tools list against supported tools."""
         for item in value:
             if isinstance(item, Tool) and type(item) not in self.tools:
-                supported = [t.__name__ for t in self.tools]
-                msg = f"Tool '{type(item).__name__}' not supported. Supported: {supported}"
+                if self.tools:
+                    supported = [t.__name__ for t in self.tools]
+                    msg = f"Tool '{type(item).__name__}' not supported. Supported: {supported}"
+                else:
+                    msg = f"Tool '{type(item).__name__}' is not supported by this model"
                 raise ConstraintViolationError(msg)
         return value
 
diff --git a/src/celeste/protocols/chatcompletions/parameters.py b/src/celeste/protocols/chatcompletions/parameters.py
index d6f2493..92b098d 100644
--- a/src/celeste/protocols/chatcompletions/parameters.py
+++ b/src/celeste/protocols/chatcompletions/parameters.py
@@ -99,7 +99,7 @@ def map(
             if isinstance(item, Tool):
                 mapper = dispatch.get(type(item))
                 if mapper is None:
-                    msg = f"Tool '{type(item).__name__}' is not supported by this provider"
+                    msg = f"Tool '{type(item).__name__}' is not supported by Chat Completions"
                     raise ValueError(msg)
                 tools.append(mapper.map_tool(item))
             elif isinstance(item, dict) and "name" in item: