diff --git a/masque/builder/pather.py b/masque/builder/pather.py
index 5fbd746..b115f65 100644
--- a/masque/builder/pather.py
+++ b/masque/builder/pather.py
@@ -324,10 +324,10 @@ class Pather(Builder):
 
         tool = self.tools.get(portspec, self.tools[None])
         in_ptype = self.pattern[portspec].ptype
-        pat = tool.path(ccw, length, in_ptype=in_ptype, port_names=tool_port_names, **kwargs)
+        tree = tool.path(ccw, length, in_ptype=in_ptype, port_names=tool_port_names, **kwargs)
         name = self.library.get_name(base_name)
-        self.library[name] = pat
-        return self.plug(Abstract(name, pat.ports), {portspec: tool_port_names[0]})
+        abstract = self.library << tree.rename_top(name)
+        return self.plug(abstract, {portspec: tool_port_names[0]})
 
     def path_to(
             self,
diff --git a/masque/builder/tools.py b/masque/builder/tools.py
index 6ff9366..2ed56d6 100644
--- a/masque/builder/tools.py
+++ b/masque/builder/tools.py
@@ -65,7 +65,7 @@ class Tool:
             out_ptype: str | None = None,
             port_names: tuple[str, str] = ('A', 'B'),
             **kwargs,
-            ) -> Pattern:
+            ) -> Library:
         """
         Create a wire or waveguide that travels exactly `length` distance along the axis
         of its input port.
@@ -246,7 +246,7 @@ class BasicTool(Tool, metaclass=ABCMeta):
             out_ptype: str | None = None,
             port_names: tuple[str, str] = ('A', 'B'),
             **kwargs,
-            ) -> Pattern:
+            ) -> Library:
         _out_port, data = self.planL(
             ccw,
             length,
@@ -270,7 +270,7 @@ class BasicTool(Tool, metaclass=ABCMeta):
             opat, oport_theirs, oport_ours = data.out_transition
             bb.plug(opat, {port_names[1]: oport_ours})
 
-        return bb.pattern
+        return tree
 
     def planL(
             self,
@@ -422,7 +422,7 @@ class PathTool(Tool, metaclass=ABCMeta):
             out_ptype: str | None = None,
             port_names: tuple[str, str] = ('A', 'B'),
             **kwargs,
-            ) -> Pattern:
+            ) -> Library:
         out_port, dxy = self.planL(
             ccw,
             length,
@@ -430,7 +430,7 @@ class PathTool(Tool, metaclass=ABCMeta):
             out_ptype=out_ptype,
             )
 
-        pat = Pattern()
+        tree, pat = Library.mktree('_path')
         pat.path(layer=self.layer, width=self.width, vertices=[(0, 0), (length, 0)])
 
         if ccw is None:
@@ -445,7 +445,7 @@ class PathTool(Tool, metaclass=ABCMeta):
             port_names[1]: Port(dxy, rotation=out_rot, ptype=self.ptype),
             }
 
-        return pat
+        return tree
 
     def planL(
             self,