diff --git a/apps/twnlua/docgen.py b/apps/twnlua/docgen.py
new file mode 100755
index 0000000..a57aba1
--- /dev/null
+++ b/apps/twnlua/docgen.py
@@ -0,0 +1,53 @@
+#!/bin/env python3
+
+import sys, json
+
+with open(sys.argv[1], 'r') if sys.argv[1] != "-" else sys.stdin as f:
+    api_source = f.read()
+
+api = json.loads(api_source)
+
+def to_lua_type_annot(typename):
+    basetype = typename.rsplit(' *', 1)[0]
+    if typename == "char *":
+        return "string"
+    elif basetype == "float":
+        return "number"
+    elif basetype == "bool":
+        return "boolean"
+    elif basetype == "Control":
+        return "Control"
+    elif basetype == "Vec2":
+        return r"{ x: number, y: number }"
+    elif basetype == "Vec3":
+        return r"{ x: number, y: number, z: number }"
+    elif basetype == "Color":
+        return r"{ r: number, g: number, b: number, a: number }"
+    elif basetype == "Rect":
+        return r"{ x: number, y: number, w: number, h: number }"
+    else:
+        return "unknown"
+        # raise BaseException("Unhandled type for annotation: %s" % typename)
+
+type_annotations, enum_annotations = {}, {}
+type_annotations["ctx"] = r"{ %s, udata: table }" % \
+    ', '.join("%s: %s" % (f["name"], to_lua_type_annot(f["type"])) for f in api["types"]["Context"]["fields"])
+
+for annot in type_annotations:
+    print("---@type " + type_annotations[annot])
+    print(r"%s = nil" % annot)
+
+enum_annotations["Control"] = \
+    '|'.join('\'"%s"\'' % e for e in api["types"]["Control"]["enums"])
+
+for annot in enum_annotations:
+    print("---@alias %s %s" % (annot, enum_annotations[annot]))
+
+procedure_annotations = {}
+for procedure, procedure_desc in api["procedures"].items():
+    procedure_annotations[procedure] = r"{ %s }" % \
+        ', '.join("%s: %s" % (p["name"], to_lua_type_annot(p["type"]) + '?' * ("default" in p)) for p in procedure_desc["params"])
+
+for annot in procedure_annotations:
+    print("---@param args " + procedure_annotations[annot])
+    print("function %s(args) end" % annot)