diff --git a/scripts/collision_from_tiled.py b/scripts/collision_from_tiled.py
new file mode 100644
index 0000000..6832d91
--- /dev/null
+++ b/scripts/collision_from_tiled.py
@@ -0,0 +1,167 @@
+"""Convert a finite Tiled JSON map to the docs/13 collision contract.
+
+Usage: python scripts/collision_from_tiled.py export.tmj
+Set string map properties region (rusty-creek), chunk (rc-0-0) and state
+(clean/anomaly). Use an orthogonal 2160x720 map. Reference image layers are
+ignored; object layer names and shapes follow docs/13. Box layers require
+Tiled rectangles, not open polylines or polygons. Object properties supply
+kind/id/damage; an object's name can supply id. Additional custom properties
+(such as pickup item) are retained unchanged. No image data is read.
+"""
+from __future__ import annotations
+
+import argparse
+import json
+import math
+import re
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+SIZE = (2160, 720)
+LAYERS = {
+    'walk': 'walk', 'slide': 'slide', 'one-way': 'oneWay',
+    'climb': 'climb', 'solid': 'solid', 'no-go': 'noGo',
+    'hazard': 'hazard', 'interact': 'interact', 'spawn': 'spawn',
+    'ledge': 'ledge', 'glide-lift': 'glideLift',
+}
+LINES = {'walk', 'slide', 'one-way'}
+POINTS = {'spawn', 'ledge'}
+
+
+def require(condition, message):
+    if not condition:
+        raise ValueError(message)
+
+
+def integer(value, context):
+    require(type(value) in (int, float) and math.isfinite(value)
+            and value == int(value), f'{context}: expected integer stage pixels')
+    return int(value)
+
+
+def slug(value, context):
+    require(isinstance(value, str) and re.fullmatch(r'[a-z][a-z0-9-]*', value),
+            f'{context}: expected a lower-case name with dashes')
+    return value
+
+
+def properties(data):
+    result = {}
+    for prop in data.get('properties', []):
+        require(prop['name'] not in result, f'duplicate property {prop["name"]}')
+        result[prop['name']] = property_value(prop)
+    return result
+
+
+def property_value(prop):
+    # Tiled 1.12 list entries carry type/value wrappers, unlike plain JSON arrays.
+    if prop.get('type') == 'list':
+        return [property_value(entry) for entry in prop['value']]
+    return prop['value']
+
+
+def point(x, y, context):
+    x, y = integer(x, context), integer(y, context)
+    require(0 <= x <= SIZE[0] and 0 <= y <= SIZE[1],
+            f'{context}: point ({x}, {y}) outside 2160x720 chunk')
+    return [x, y]
+
+
+def convert(data):
+    """Return (region, collision); reject unsupported authoring, never infer it."""
+    require(data.get('type') == 'map' and data.get('orientation') == 'orthogonal'
+            and not data.get('infinite', False), 'expected a finite orthogonal Tiled map')
+    for axis, tile, expected in [('width', 'tilewidth', 2160), ('height', 'tileheight', 720)]:
+        count, pixels = integer(data[axis], axis), integer(data[tile], tile)
+        require(count > 0 and pixels > 0 and count * pixels == expected,
+                'map must cover exactly 2160x720 stage pixels')
+    meta = properties(data)
+    region = slug(meta.get('region'), 'map region')
+    chunk = slug(meta.get('chunk'), 'map chunk')
+    state = meta.get('state')
+    require(state in ('clean', 'anomaly'), 'map state must be clean or anomaly')
+    result = {'chunk': chunk, 'state': state, 'size': list(SIZE),
+              **{name: [] for name in LAYERS.values()}}
+    identifiers = set()
+    for layer in data['layers']:
+        if layer.get('type') == 'imagelayer':
+            continue  # The composed chunk is an authoring backdrop, never collision.
+        name = layer.get('name')
+        require(name in LAYERS, f'unknown collision layer {name!r}')
+        require(layer.get('type') == 'objectgroup', f'{name}: expected an object layer')
+        offset_x = integer(layer.get('offsetx', 0), name)
+        offset_y = integer(layer.get('offsety', 0), name)
+        require(layer.get('x', 0) == 0 and layer.get('y', 0) == 0,
+                f'{name}: use pixel offsets, not tile offsets')
+        for obj in layer['objects']:
+            context = f'{name} object {obj.get("id", "?")}'
+            require(obj.get('rotation', 0) == 0, f'{context}: rotation is unsupported')
+            require(not any(key in obj for key in ('gid', 'template', 'text'))
+                    and not obj.get('ellipse') and not obj.get('capsule'),
+                    f'{context}: unsupported object shape')
+            x, y = point(integer(obj['x'], context) + offset_x,
+                         integer(obj['y'], context) + offset_y, context)
+            if name in LINES:
+                require('polyline' in obj and not obj.get('point') and 'polygon' not in obj,
+                        f'{context}: expected a polyline')
+                vertices = [point(x + p['x'], y + p['y'], context) for p in obj['polyline']]
+                require(len(vertices) >= 2, f'{context}: polyline needs at least two points')
+                require(all(a[0] < b[0] for a, b in zip(vertices, vertices[1:])),
+                        f'{context}: polyline must run strictly left to right')
+                result[LAYERS[name]].append(vertices)
+                continue
+            require('polyline' not in obj and 'polygon' not in obj,
+                    f'{context}: expected a closed rectangle or point, not an open box')
+            item = {'x': x, 'y': y}
+            if name in POINTS:
+                require(obj.get('point') is True and obj.get('width', 0) == 0
+                        and obj.get('height', 0) == 0, f'{context}: expected a Tiled point')
+            else:
+                w, h = integer(obj['width'], context), integer(obj['height'], context)
+                require(not obj.get('point') and w > 0 and h > 0,
+                        f'{context}: rectangle must have positive width and height')
+                point(x + w, y + h, context)
+                item.update(w=w, h=h)
+            props = properties(obj)
+            require(not {'x', 'y', 'w', 'h'} & props.keys(),
+                    f'{context}: custom properties cannot override geometry')
+            # Encounter metadata belongs to the level author, not this converter.
+            item.update({key: value for key, value in props.items() if key not in ('kind', 'id')})
+            for field in ('kind', 'id'):
+                value = props.get(field, obj.get('name') if field == 'id' else None)
+                if value:
+                    item[field] = slug(value, f'{context} {field}')
+            required = {'climb': ('kind',), 'interact': ('kind', 'id'), 'spawn': ('kind', 'id')}
+            for field in required.get(name, ()):
+                require(field in item, f'{context}: missing {field} property')
+            if 'id' in item:
+                require(item['id'] not in identifiers, f'{context}: duplicate id {item["id"]}')
+                identifiers.add(item['id'])
+            if name == 'hazard':
+                damage = integer(props.get('damage'), f'{context} damage')
+                require(damage > 0, f'{context}: damage must be positive')
+                item['damage'] = damage
+            result[LAYERS[name]].append(item)
+    return region, result
+
+
+def write_collision(source, root=ROOT):
+    region, collision = convert(json.loads(Path(source).read_text(encoding='utf-8-sig')))
+    output = Path(root) / 'art' / 'stages' / region / f'{collision["chunk"]}.{collision["state"]}.collision.json'
+    output.parent.mkdir(parents=True, exist_ok=True)
+    output.write_text(json.dumps(collision, indent=2) + '\n', encoding='utf-8')
+    return output
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('source', type=Path, help='Tiled JSON map (.tmj or .json)')
+    args = parser.parse_args()
+    try:
+        print(write_collision(args.source))
+    except (ValueError, KeyError, TypeError, OSError) as error:
+        parser.exit(1, f'Collision export failed: {error}\n')
+
+
+if __name__ == '__main__':
+    main()
diff --git a/scripts/test_collision_from_tiled.py b/scripts/test_collision_from_tiled.py
new file mode 100644
index 0000000..a82e0fc
--- /dev/null
+++ b/scripts/test_collision_from_tiled.py
@@ -0,0 +1,177 @@
+"""Small hand-authored Tiled export covering every docs/13 collision layer."""
+import copy
+import json
+import shutil
+import subprocess
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+from collision_from_tiled import LAYERS, convert, write_collision
+
+
+def props(**values):
+    def typed(value):
+        if isinstance(value, list):
+            return {'type': 'list', 'value': [typed(item) for item in value]}
+        return {'type': {int: 'int', bool: 'bool', str: 'string'}[type(value)], 'value': value}
+    return [{'name': key, **typed(value)} for key, value in values.items()]
+
+
+def fixture():
+    layers = []
+    for index, name in enumerate(LAYERS):
+        obj = {'id': index + 1, 'x': 100, 'y': 200, 'width': 30, 'height': 40, 'rotation': 0}
+        if name in ('walk', 'slide', 'one-way'):
+            obj.update(width=0, height=0, polyline=[{'x': 0, 'y': 0}, {'x': 80, 'y': -20}])
+        elif name in ('spawn', 'ledge'):
+            obj.update(width=0, height=0, point=True)
+        if name in ('climb', 'interact', 'spawn'):
+            kind = {'climb': 'ladder', 'interact': 'coffee-machine', 'spawn': 'player'}[name]
+            obj['properties'] = props(kind=kind, id=f'{name}-one')
+        if name == 'hazard':
+            obj['properties'] = props(damage=1)
+        layers.append({'type': 'objectgroup', 'name': name, 'objects': [obj]})
+    return {'type': 'map', 'orientation': 'orthogonal', 'infinite': False,
+            'width': 135, 'height': 45, 'tilewidth': 16, 'tileheight': 16,
+            'properties': props(region='rusty-creek', chunk='rc-0-0', state='anomaly'),
+            'layers': layers}
+
+
+class CollisionFromTiledTests(unittest.TestCase):
+    def setUp(self):
+        self.data = fixture()
+
+    def object(self, name):
+        return next(layer['objects'][0] for layer in self.data['layers'] if layer['name'] == name)
+
+    def test_exports_all_contract_shapes_and_destination(self):
+        with tempfile.TemporaryDirectory() as folder:
+            source = Path(folder) / 'example.tmj'
+            source.write_text(json.dumps(self.data), encoding='utf-8')
+            output = write_collision(source, folder)
+            self.assertEqual(output.relative_to(folder).as_posix(),
+                             'art/stages/rusty-creek/rc-0-0.anomaly.collision.json')
+            actual = json.loads(output.read_text())
+        self.assertEqual(actual['size'], [2160, 720])
+        self.assertEqual(actual['walk'], [[[100, 200], [180, 180]]])
+        self.assertEqual(actual['oneWay'], actual['walk'])
+        self.assertEqual(actual['climb'], [dict(x=100, y=200, w=30, h=40, kind='ladder', id='climb-one')])
+        self.assertEqual(actual['spawn'], [dict(x=100, y=200, kind='player', id='spawn-one')])
+        self.assertEqual(actual['hazard'], [dict(x=100, y=200, w=30, h=40, damage=1)])
+        self.assertTrue(all(len(actual[key]) == 1 for key in LAYERS.values()))
+
+    def test_layer_offset_and_image_backdrop(self):
+        self.data['layers'][0].update(offsetx=10, offsety=-20)
+        self.data['layers'].append({'type': 'imagelayer', 'name': 'composed chunk', 'image': 'chunk.png'})
+        self.assertEqual(convert(self.data)[1]['walk'], [[[110, 180], [190, 160]]])
+
+    def test_unknown_layer_and_wrong_layer_type(self):
+        for changes in ({'name': 'typo'}, {'type': 'tilelayer'}):
+            with self.subTest(changes=changes):
+                data = copy.deepcopy(self.data)
+                data['layers'][0].update(changes)
+                with self.assertRaises(ValueError):
+                    convert(data)
+
+    def test_open_and_degenerate_boxes_fail(self):
+        for changes in ({'polyline': [{'x': 0, 'y': 0}, {'x': 30, 'y': 40}]},
+                        {'polygon': []}, {'width': 0}, {'height': -1}, {'rotation': 45}):
+            with self.subTest(changes=changes):
+                data = copy.deepcopy(self.data)
+                data['layers'][3]['objects'][0].update(changes)
+                with self.assertRaises(ValueError):
+                    convert(data)
+
+    def test_out_of_bounds_points_lines_and_boxes_fail(self):
+        for name, changes in [('spawn', {'x': 2161}), ('ledge', {'y': -1}),
+                              ('solid', {'x': 2150}), ('walk', {'x': 2150})]:
+            with self.subTest(name=name):
+                data = copy.deepcopy(self.data)
+                obj = next(layer['objects'][0] for layer in data['layers'] if layer['name'] == name)
+                obj.update(changes)
+                with self.assertRaisesRegex(ValueError, 'outside'):
+                    convert(data)
+
+    def test_fractional_nonfinite_and_bool_coordinates_fail(self):
+        for value in (0.5, float('nan'), float('inf'), True):
+            with self.subTest(value=value):
+                self.object('spawn')['x'] = value
+                with self.assertRaises(ValueError):
+                    convert(self.data)
+
+    def test_leftward_or_vertical_ground_fails(self):
+        for x in (-1, 0):
+            self.object('walk')['polyline'][1]['x'] = x
+            with self.assertRaisesRegex(ValueError, 'left to right'):
+                convert(self.data)
+
+    def test_missing_metadata_or_traversal_never_writes(self):
+        for metadata in (props(), props(region='../escape', chunk='rc-0-0', state='clean'),
+                         props(region='rusty-creek', chunk='rc-0-0', state='wrong')):
+            self.data['properties'] = metadata
+            with self.assertRaises(ValueError):
+                convert(self.data)
+
+    def test_required_object_properties_and_unique_ids(self):
+        self.object('spawn')['properties'] = props(kind='player')
+        with self.assertRaisesRegex(ValueError, 'missing id'):
+            convert(self.data)
+        self.object('spawn')['properties'] = props(kind='player', id='climb-one')
+        with self.assertRaisesRegex(ValueError, 'duplicate id'):
+            convert(self.data)
+
+    def test_encounter_properties_survive_export_without_losing_types(self):
+        self.object('interact')['properties'] = props(kind='pickup', id='chair', item='chair',
+                                                     note='First weapon', enabled=True)
+        self.object('spawn')['properties'] = props(kind='rover', id='rover-1', patrol=[640, 880])
+        actual = convert(self.data)[1]
+        self.assertEqual(actual['interact'][0], dict(x=100, y=200, w=30, h=40,
+                         kind='pickup', id='chair', item='chair', note='First weapon', enabled=True))
+        self.assertEqual(actual['spawn'][0]['patrol'], [640, 880])
+
+    def test_tiled_nested_list_entries_are_decoded(self):
+        self.object('spawn')['properties'] = props(kind='rover', id='rover-1', route=[[100, 200], [300, 400]])
+        self.assertEqual(convert(self.data)[1]['spawn'][0]['route'], [[100, 200], [300, 400]])
+
+    def test_custom_properties_cannot_replace_geometry(self):
+        for key in ('x', 'y', 'w', 'h'):
+            with self.subTest(key=key):
+                self.object('interact')['properties'] = props(kind='pickup', id='chair', **{key: -1})
+                with self.assertRaisesRegex(ValueError, 'override geometry'):
+                    convert(self.data)
+
+    def test_failed_conversion_does_not_overwrite_existing_output(self):
+        with tempfile.TemporaryDirectory() as folder:
+            source = Path(folder) / 'example.tmj'
+            source.write_text(json.dumps(self.data))
+            output = write_collision(source, folder)
+            original = output.read_bytes()
+            self.object('solid')['width'] = 0
+            source.write_text(json.dumps(self.data))
+            with self.assertRaises(ValueError):
+                write_collision(source, folder)
+            self.assertEqual(output.read_bytes(), original)
+
+    def test_cli_writes_contract_and_exits_loudly_on_bad_input(self):
+        with tempfile.TemporaryDirectory() as folder:
+            root = Path(folder)
+            (root / 'scripts').mkdir()
+            script = root / 'scripts' / 'collision_from_tiled.py'
+            shutil.copy(Path(__file__).with_name('collision_from_tiled.py'), script)
+            source = root / 'export.tmj'
+            source.write_text(json.dumps(self.data))
+            command = [sys.executable, str(script), str(source)]
+            good = subprocess.run(command, capture_output=True, text=True)
+            self.assertEqual(good.returncode, 0, good.stderr)
+            self.assertTrue((root / 'art/stages/rusty-creek/rc-0-0.anomaly.collision.json').exists())
+            self.data['layers'][0]['name'] = 'typo'
+            source.write_text(json.dumps(self.data))
+            bad = subprocess.run(command, capture_output=True, text=True)
+            self.assertEqual(bad.returncode, 1)
+            self.assertIn('unknown collision layer', bad.stderr)
+
+
+if __name__ == '__main__':
+    unittest.main()