diff --git a/key_decoder.py b/key_decoder.py
new file mode 100644
index 0000000..a92bde4
--- /dev/null
+++ b/key_decoder.py
@@ -0,0 +1,61 @@
+import cadquery as cq
+from cadquery import exporters
+
+import key_bittings
+from key_bittings import BittingSpecification
+
+kerf = .11
+
+bitting_width = 5
+
+text_size = 5
+text_gap = 2
+
+margins = 5
+margin_radius = 2
+
+
+def bitting(loc: cq.Location, name: str, depth: float):
+    # can only make text in a 3D workplane, so make it in 3D and extract the face
+    text = (
+        cq.Workplane()
+        .text(name, fontsize=text_size, distance=1, valign="top", halign="center")
+        .edges("<Z")
+    )
+
+    return (
+        cq.Sketch()
+        .push([(0, depth/2)]).rect(bitting_width, depth - kerf)
+        .push([(0, -text_gap)]).face(text.vals())
+        .moved(loc)
+    )
+
+
+def decoder_card(spec: BittingSpecification):
+    result = (
+        cq.Sketch()
+        .rect(margins * 2 + bitting_width * len(spec.depths),
+              margins * 2 + text_size + text_gap + max(*spec.depths.values()))
+        .vertices().fillet(margin_radius).reset()
+    )
+
+    depths = iter(spec.depths.items())
+
+    result = (
+        result
+        .rarray(bitting_width, 0, len(spec.depths), 1)
+        .each(lambda loc: bitting(loc, *next(depths)), mode="s")
+    )
+
+    return result
+
+
+sketch = decoder_card(key_bittings.national_disc_tumbler)
+
+# for preview/export purposes, a 3D object is more convenient
+result = cq.Workplane("front").workplane().placeSketch(sketch).extrude(1)
+exporters.export(result, "national_disc_tumbler_decoder.svg", opt={
+    "showAxes": False,
+    "projectionDir": (0, 0, 1),
+    "strokeColor": (255, 0, 0),
+})