diff --git a/masque/builder/__init__.py b/masque/builder/__init__.py
index 50ddcee..0c083b7 100644
--- a/masque/builder/__init__.py
+++ b/masque/builder/__init__.py
@@ -1,2 +1,3 @@
 from .devices import Port, Device
 from .utils import ell
+from .tools import Tool
diff --git a/masque/builder/devices.py b/masque/builder/devices.py
index e938ce5..1aebb56 100644
--- a/masque/builder/devices.py
+++ b/masque/builder/devices.py
@@ -15,6 +15,8 @@ from ..subpattern import SubPattern
 from ..traits import PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable
 from ..utils import AutoSlots, rotation_matrix_2d
 from ..error import DeviceError
+from .tools import Tool
+from .utils import ell
 
 
 logger = logging.getLogger(__name__)
@@ -157,7 +159,7 @@ class Device(Copyable, Mirrorable):
         renamed to 'gnd' so that further routing can use this signal or net name
         rather than the port name on the original `pad` device.
     """
-    __slots__ = ('pattern', 'ports', '_dead')
+    __slots__ = ('pattern', 'ports', 'tools', '_dead')
 
     pattern: Pattern
     """ Layout of this device """
@@ -165,6 +167,12 @@ class Device(Copyable, Mirrorable):
     ports: Dict[str, Port]
     """ Uniquely-named ports which can be used to snap to other Device instances"""
 
+    tools: Dict[Optional[str], Tool]
+    """
+    Tool objects are used to dynamically generate new single-use Devices
+    (e.g wires or waveguides) to be plugged into this device.
+    """
+
     _dead: bool
     """ If True, plug()/place() are skipped (for debugging)"""
 
@@ -173,6 +181,7 @@ class Device(Copyable, Mirrorable):
             pattern: Optional[Pattern] = None,
             ports: Optional[Dict[str, Port]] = None,
             *,
+            tools: Optional[Dict[Optional[str], Tool]] = None,
             name: Optional[str] = None,
             ) -> None:
         """
@@ -198,6 +207,11 @@ class Device(Copyable, Mirrorable):
         else:
             self.ports = copy.deepcopy(ports)
 
+        if tools is None:
+            self.tools = {}
+        else:
+            self.tools = tools
+
         self._dead = False
 
     @overload
@@ -205,7 +219,7 @@ class Device(Copyable, Mirrorable):
         pass
 
     @overload
-    def __getitem__(self, key: Union[List[str], Tuple[str], KeysView[str], ValuesView[str]]) -> Dict[str, Port]:
+    def __getitem__(self, key: Union[List[str], Tuple[str, ...], KeysView[str], ValuesView[str]]) -> Dict[str, Port]:
         pass
 
     def __getitem__(self, key: Union[str, Iterable[str]]) -> Union[Port, Dict[str, Port]]:
@@ -333,7 +347,7 @@ class Device(Copyable, Mirrorable):
         """
         pat = Pattern(name)
         pat.addsp(self.pattern)
-        new = Device(pat, ports=self.ports)
+        new = Device(pat, ports=self.ports, tools=self.tools)
         return new
 
     def as_interface(
@@ -408,7 +422,7 @@ class Device(Copyable, Mirrorable):
         if duplicates:
             raise DeviceError(f'Duplicate keys after prefixing, try a different prefix: {duplicates}')
 
-        new = Device(name=name, ports={**ports_in, **ports_out})
+        new = Device(name=name, ports={**ports_in, **ports_out}, tools=self.tools)
         return new
 
     def plug(
@@ -752,6 +766,99 @@ class Device(Copyable, Mirrorable):
         s += ']>'
         return s
 
+    def retool(
+            self: D,
+            tool: Tool,
+            keys: Union[Optional[str], Sequence[Optional[str]]] = None,
+            ) -> D:
+        if keys is None or isinstance(keys, str):
+            self.tools[keys] = tool
+        else:
+            for key in keys:
+                self.tools[key] = tool
+        return self
+
+    def path(
+            self: D,
+            portspec: str,
+            ccw: Optional[bool],
+            length: float,
+            *,
+            tool_port_names: Sequence[str] = ('A', 'B'),
+            **kwargs,
+            ) -> D:
+        if self._dead:
+            logger.error('Skipping path() since device is dead')
+            return self
+
+        tool = self.tools.get(portspec, self.tools[None])
+        in_ptype = self.ports[portspec].ptype
+        dev = tool.path(ccw, length, in_ptype=in_ptype, port_names=tool_port_names, **kwargs)
+        return self.plug(dev, {portspec: tool_port_names[0]})
+
+    def path_to(
+            self: D,
+            portspec: str,
+            ccw: Optional[bool],
+            position: float,
+            *,
+            tool_port_names: Sequence[str] = ('A', 'B'),
+            **kwargs,
+            ) -> D:
+        if self._dead:
+            logger.error('Skipping path_to() since device is dead')
+            return self
+
+        port = self.ports[portspec]
+        x, y = port.offset
+        if port.rotation is None:
+            raise DeviceError(f'Port {portspec} has no rotation and cannot be used for path_to()')
+
+        if not numpy.isclose(port.rotation % (pi / 2), 0):
+            raise DeviceError('path_to was asked to route from non-manhattan port')
+
+        is_horizontal = numpy.isclose(port.rotation % pi, 0)
+        if is_horizontal:
+            if numpy.sign(numpy.cos(port.rotation)) == numpy.sign(position - x):
+                raise DeviceError(f'path_to routing to behind source port: x={x:g} to {position:g}')
+            length = numpy.abs(position - x)
+        else:
+            if numpy.sign(numpy.sin(port.rotation)) == numpy.sign(position - y):
+                raise DeviceError(f'path_to routing to behind source port: y={y:g} to {position:g}')
+            length = numpy.abs(position - y)
+
+        return self.path(portspec, ccw, length, tool_port_names=tool_port_names, **kwargs)
+
+    def busL(
+            self: D,
+            portspec: Union[str, Sequence[str]],
+            ccw: Optional[bool],
+            bound_type: str,
+            bound: Union[float, ArrayLike],
+            *,
+            spacing: Optional[Union[float, ArrayLike]] = None,
+            set_rotation: Optional[float] = None,
+            tool_port_names: Sequence[str] = ('A', 'B'),
+            name: str = '_busL',
+            ) -> D:
+        if self._dead:
+            logger.error('Skipping busL() since device is dead')
+            return self
+
+        if isinstance(portspec, str):
+            portspec = [portspec]
+        ports = self[tuple(portspec)]
+
+        extensions = ell(ports, ccw, spacing=spacing, bound=bound, bound_type=bound_type, set_rotation=set_rotation)
+
+        dev = Device(name='', ports=ports, tools=self.tools).as_interface(name)
+        for name, length in extensions.items():
+            dev.path(name, ccw, length, tool_port_names=tool_port_names)
+
+        return self.plug(dev, {sp: 'in_' + sp for sp in ports.keys()})       # TODO safe to use 'in_'?
+
+    # TODO def path_join() and def bus_join()?
+
 
 def rotate_offsets_around(
         offsets: NDArray[numpy.float64],
diff --git a/masque/builder/tools.py b/masque/builder/tools.py
new file mode 100644
index 0000000..bd93f0c
--- /dev/null
+++ b/masque/builder/tools.py
@@ -0,0 +1,22 @@
+"""
+Tools are objects which dynamically generate simple single-use devices (e.g. wires or waveguides)
+"""
+from typing import TYPE_CHECKING, Optional, Sequence
+
+if TYPE_CHECKING:
+    from .devices import Device
+
+
+class Tool:
+    def path(
+            self,
+            ccw: Optional[bool],
+            length: float,
+            *,
+            in_ptype: Optional[str] = None,
+            out_ptype: Optional[str] = None,
+            port_names: Sequence[str] = ('A', 'B'),
+            **kwargs,
+            ) -> 'Device':
+        raise NotImplementedError(f'path() not implemented for {type(self)}')
+