diff --git a/script/odoo/migration/check_cow_views.py b/script/odoo/migration/check_cow_views.py
new file mode 100755
index 0000000..6255482
--- /dev/null
+++ b/script/odoo/migration/check_cow_views.py
@@ -0,0 +1,235 @@
+#!/usr/bin/env python3
+# © 2021-2026 TechnoLibre (http://www.technolibre.ca)
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl)
+
+"""Predict which website COW views will break on the next version bump.
+
+Background
+----------
+When a website view is customized, Odoo makes a copy-on-write (COW) copy tied
+to a website_id. That copy freezes the arch AND the structure of the module
+view it was copied from.
+
+A module view can change structure between two Odoo versions. Example measured
+on a real 12.0 database: ``portal.frontend_layout`` is declared ``primary`` in
+12.0 (a full QWeb template) and becomes an ``extension`` in 13.0
+(``inherit_id="web.frontend_layout"`` + xpath). During the upgrade the COW copy
+follows the module and becomes an extension, but keeps its 12.0 full-template
+arch. Odoo then applies the ``<t t-name=...>`` root as an inheritance spec,
+cannot find it in the parent, and the whole upgrade stops on::
+
+    ValueError: Element '<t ... t-name="portal.frontend_layout">'
+                cannot be located in parent view
+
+So the rule is:
+
+    a COW view breaks when its module counterpart changes ``mode``
+    between version N and version N+1.
+
+That is predictable *before* starting a multi-hour migration: the current mode
+is in the database, and the target mode is declared in the target version
+sources. This script compares the two and reports the views at risk.
+
+It only reads: no database write, no source modification.
+"""
+
+import argparse
+import glob
+import os
+import subprocess
+import sys
+import xml.etree.ElementTree as ET
+
+# A view whose module counterpart cannot be found is reported separately: it is
+# usually a view of a module that does not exist in the target version.
+MODE_UNKNOWN = "unknown"
+
+
+def query_cow_views(database):
+    """Return [(id, key, mode, website_id)] for every website COW view."""
+    sql = (
+        "SELECT id, COALESCE(key, ''), mode, website_id FROM ir_ui_view"
+        " WHERE website_id IS NOT NULL ORDER BY id;"
+    )
+    result = subprocess.run(
+        ["psql", "-d", database, "-tAF", "|", "-c", sql],
+        capture_output=True,
+        text=True,
+    )
+    if result.returncode:
+        raise RuntimeError(
+            f"Cannot read views from '{database}': {result.stderr.strip()}"
+        )
+    lst_view = []
+    for line in result.stdout.splitlines():
+        if not line.strip():
+            continue
+        view_id, key, mode, website_id = line.split("|")
+        lst_view.append((int(view_id), key, mode, website_id))
+    return lst_view
+
+
+def find_module_dir(odoo_version, module_name):
+    """Locate a module directory inside an odoo<version> tree."""
+    lst_pattern = [
+        os.path.join(odoo_version, "odoo", "addons", module_name),
+        os.path.join(odoo_version, "odoo", "odoo", "addons", module_name),
+        os.path.join(odoo_version, "addons", "*", module_name),
+    ]
+    for pattern in lst_pattern:
+        for path in sorted(glob.glob(pattern)):
+            if os.path.isdir(path):
+                return path
+    return None
+
+
+def declared_mode(module_dir, template_id):
+    """Return 'primary', 'extension' or None for a view declared in sources.
+
+    Handles both declaration styles: <template id="..."> and
+    <record model="ir.ui.view">. A view is an extension when it inherits and is
+    not explicitly flagged primary.
+    """
+    pattern = os.path.join(module_dir, "**", "*.xml")
+    for file_path in sorted(glob.glob(pattern, recursive=True)):
+        try:
+            root = ET.parse(file_path).getroot()
+        except ET.ParseError:
+            continue
+        for element in root.iter():
+            if element.get("id") != template_id:
+                continue
+            if element.tag == "template":
+                if str(element.get("primary", "")).lower() in ("true", "1"):
+                    return "primary"
+                return "extension" if element.get("inherit_id") else "primary"
+            if (
+                element.tag == "record"
+                and element.get("model") == "ir.ui.view"
+            ):
+                mode = None
+                inherit = None
+                for field in element.findall("field"):
+                    if field.get("name") == "mode":
+                        mode = (field.text or "").strip()
+                    elif field.get("name") == "inherit_id":
+                        inherit = field
+                if mode:
+                    return mode
+                return "extension" if inherit is not None else "primary"
+    return None
+
+
+def analyse(database, target_version):
+    """Sort COW views into three buckets by comparing with the target sources.
+
+    - at_risk        : the module view changes mode -> the copy will break
+    - module_absent  : the module itself is gone in the target version
+    - no_counterpart : no module view with that id, so it is a page or a record
+                       created from the editor. Normal, and not at risk.
+    """
+    lst_at_risk = []
+    lst_module_absent = []
+    lst_no_counterpart = []
+    cache_mode = {}
+
+    for view_id, key, mode, website_id in query_cow_views(database):
+        if not key or "." not in key:
+            continue
+        if key not in cache_mode:
+            module_name, _, template_id = key.partition(".")
+            module_dir = find_module_dir(target_version, module_name)
+            if module_dir is None:
+                cache_mode[key] = MODE_UNKNOWN
+            else:
+                cache_mode[key] = declared_mode(module_dir, template_id)
+        target_mode = cache_mode[key]
+        if target_mode == MODE_UNKNOWN:
+            lst_module_absent.append((view_id, key, mode, website_id))
+        elif target_mode is None:
+            lst_no_counterpart.append((view_id, key, mode, website_id))
+        elif target_mode != mode:
+            lst_at_risk.append((view_id, key, mode, target_mode, website_id))
+    return lst_at_risk, lst_module_absent, lst_no_counterpart
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description=(
+            "Report website COW views that will break on the next Odoo"
+            " version bump (read-only)."
+        )
+    )
+    parser.add_argument(
+        "-d", "--database", required=True, help="database to inspect"
+    )
+    parser.add_argument(
+        "-t",
+        "--target_version",
+        required=True,
+        help="target Odoo source directory, e.g. odoo13.0",
+    )
+    parser.add_argument(
+        "-v",
+        "--verbose",
+        action="store_true",
+        help="also list the editor-made pages, which are not at risk",
+    )
+    config = parser.parse_args()
+
+    if not os.path.isdir(config.target_version):
+        print(
+            f"❌ Target version directory '{config.target_version}' not found."
+        )
+        return 1
+
+    lst_at_risk, lst_module_absent, lst_no_counterpart = analyse(
+        config.database, config.target_version
+    )
+
+    if not lst_at_risk:
+        print(
+            "✅ -> No website COW view changes mode in"
+            f" {config.target_version}."
+        )
+    else:
+        print(
+            f"⚠️ {len(lst_at_risk)} website COW view(s) will break when moving"
+            f" to {config.target_version}: the module view changes mode, but"
+            " the copy keeps an arch written for the old mode."
+        )
+        for view_id, key, mode, target_mode, website_id in lst_at_risk:
+            print(
+                f"   - id={view_id} website={website_id} {key}"
+                f" : {mode} -> {target_mode}"
+            )
+        print(
+            "   Arbitrate BEFORE launching the migration: reset the copy on the"
+            " module view, deactivate it (active=False, reversible), or rewrite"
+            " the customization for the target version."
+        )
+
+    if lst_module_absent:
+        print(
+            f"ℹ {len(lst_module_absent)} COW view(s) belong to a module absent"
+            f" from {config.target_version}:"
+        )
+        for view_id, key, mode, website_id in lst_module_absent:
+            print(f"   - id={view_id} website={website_id} {key} ({mode})")
+
+    if lst_no_counterpart:
+        print(
+            f"ℹ {len(lst_no_counterpart)} COW view(s) are pages or records made"
+            " from the website editor (no module view of that name): not at"
+            " risk." + ("" if config.verbose else " Use -v to list them.")
+        )
+        if config.verbose:
+            for view_id, key, mode, website_id in lst_no_counterpart:
+                print(f"   - id={view_id} website={website_id} {key} ({mode})")
+
+    # Informative only: never fail the migration on a warning.
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/script/todo/todo_upgrade.py b/script/todo/todo_upgrade.py
index fd50ef6..34e51fc 100755
--- a/script/todo/todo_upgrade.py
+++ b/script/todo/todo_upgrade.py
@@ -845,7 +845,11 @@ class TodoUpgrade:
                 for name, reason, origin in lst_uninstall_reason:
                     print(
                         f"   - {name}"
-                        + (f" — {reason}" if reason else " — ⚠️ no reason given")
+                        + (
+                            f" — {reason}"
+                            if reason
+                            else " — ⚠️ no reason given"
+                        )
                         + f"  [{origin}]"
                     )
 
@@ -891,7 +895,10 @@ class TodoUpgrade:
         print(f"🔷 {msg}")
         self.add_comment_progression(msg)
 
-        if not self.dct_progression.get("state_2_update_all") and not already_update_state_1:
+        if (
+            not self.dct_progression.get("state_2_update_all")
+            and not already_update_state_1
+        ):
             status, cmd_executed = self.todo_upgrade_execute(
                 f"./script/addons/update_addons_all.sh {database_name}",
                 single_source_odoo=True,
@@ -900,6 +907,20 @@ class TodoUpgrade:
                 self.dct_progression["state_2_update_all"] = True
                 self.write_config()
 
+        # Predict the website COW views that the NEXT version bump will break.
+        # A copy-on-write view freezes the structure of the module view it was
+        # copied from; when that module view changes mode between two versions,
+        # the copy keeps an arch written for the old mode and the upgrade dies
+        # on « Element ... cannot be located in parent view ». Reporting it here
+        # -- before hours of migration -- leaves time to arbitrate.
+        # Only the next bump can be predicted: the modes in database describe
+        # the current version.
+        self.todo_upgrade_execute(
+            f"{PYTHON_BIN} ./script/odoo/migration/check_cow_views.py"
+            f" -d {database_name} -t odoo{start_version + 1}.0",
+            wait_at_error=False,
+        )
+
         msg = "3 - Clean up database before data migration"
         print(f"🔷 {msg}")
         self.add_comment_progression(msg)