diff --git a/fusion_accounting/tools/README.md b/fusion_accounting/tools/README.md
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+# Fusion Accounting Tooling
+
+## check_odoo_diff.sh
+
+Diff a single Odoo Enterprise accounting module across two pinned snapshots
+in `RePackaged-Odoo/` and produce a categorized change report (markdown).
+
+### Usage
+
+    tools/check_odoo_diff.sh <module> <from_version> <to_version> [<output_md>]
+
+### Example
+
+    # When Odoo 20 ships, get a full report on what changed in account_accountant
+    tools/check_odoo_diff.sh account_accountant v19 v20 > reports/v20_accountant.md
+
+### Classification tags
+
+- `[MIRROR]` — mechanical port required (view XML, OWL component, PDF template, wizard view)
+- `[ABSTRACT]` — verify our adapter still aligns; update if Odoo's public API surface changed
+- `[MANIFEST]` — manifest changes (deps, asset bundles, version, hooks)
+- `[TEST]` — Odoo's tests changed; check if our equivalents need updates
+- `[REVIEW]` — uncategorized; manual review needed
+
+### Snapshot conventions
+
+Snapshots live at `$REPACKAGED_ODOO_ROOT/accounting-<version>/<module>` (default
+root: `/Users/gurpreet/Github/RePackaged-Odoo`). Override the root with the
+`REPACKAGED_ODOO_ROOT` env var.
+
+The current workspace has only the V19 snapshot at
+`/Users/gurpreet/Github/RePackaged-Odoo/accounting/` (unversioned). When
+Odoo 20 ships:
+
+1. Rename the current snapshot: `mv accounting accounting-v19`
+2. Drop the new V20 source at `accounting-v20/`
+3. Run `tools/check_odoo_diff.sh account_accountant v19 v20` per sub-module
diff --git a/fusion_accounting/tools/check_odoo_diff.sh b/fusion_accounting/tools/check_odoo_diff.sh
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+#!/usr/bin/env bash
+# check_odoo_diff.sh
+#
+# Diff a single Odoo Enterprise accounting module across two pinned snapshots
+# and produce a categorized change report.
+#
+# Usage:
+#   tools/check_odoo_diff.sh <module> <from_version> <to_version> [<output_md>]
+#
+# Example:
+#   tools/check_odoo_diff.sh account_accountant v19 v20 reports/v20_accountant_diff.md
+
+set -euo pipefail
+
+MODULE="${1:?Usage: check_odoo_diff.sh <module> <from_version> <to_version> [<output_md>]}"
+FROM="${2:?from_version required (e.g. v19)}"
+TO="${3:?to_version required (e.g. v20)}"
+OUT="${4:-/dev/stdout}"
+
+ROOT="${REPACKAGED_ODOO_ROOT:-/Users/gurpreet/Github/RePackaged-Odoo}"
+FROM_DIR="$ROOT/accounting-$FROM/$MODULE"
+TO_DIR="$ROOT/accounting-$TO/$MODULE"
+
+if [ ! -d "$FROM_DIR" ]; then
+    echo "ERROR: $FROM_DIR does not exist. Snapshot $FROM not yet present?" >&2
+    exit 1
+fi
+if [ ! -d "$TO_DIR" ]; then
+    echo "ERROR: $TO_DIR does not exist. Snapshot $TO not yet present?" >&2
+    exit 1
+fi
+
+classify() {
+    local f="$1"
+    case "$f" in
+        */views/*|*/static/src/components/*|*/report/*|*/wizard/*_views.xml|*/wizards/*_views.xml)
+            echo "[MIRROR]" ;;
+        */models/*_engine.py|*/services/*)
+            echo "[ABSTRACT]" ;;
+        */__manifest__.py)
+            echo "[MANIFEST]" ;;
+        */tests/*)
+            echo "[TEST]" ;;
+        *)
+            echo "[REVIEW]" ;;
+    esac
+}
+
+{
+    echo "# Diff Report: $MODULE ($FROM -> $TO)"
+    echo ""
+    echo "Generated: $(date '+%Y-%m-%d %H:%M:%S')"
+    echo ""
+    echo "## Changed Files (with classification suggestion)"
+    echo ""
+    diff -ruN --brief "$FROM_DIR" "$TO_DIR" | while read -r line; do
+        case "$line" in
+            "Files "*" and "*" differ")
+                file=$(echo "$line" | sed -E 's/^Files (.+) and .+ differ$/\1/' | sed "s|$FROM_DIR/||")
+                tag=$(classify "$file")
+                echo "- $tag \`$file\`"
+                ;;
+            "Only in $TO_DIR"*)
+                file=$(echo "$line" | sed -E "s|Only in $TO_DIR(.*): (.+)|\1/\2|" | sed "s|^/||")
+                tag=$(classify "$file")
+                echo "- $tag NEW: \`$file\`"
+                ;;
+            "Only in $FROM_DIR"*)
+                file=$(echo "$line" | sed -E "s|Only in $FROM_DIR(.*): (.+)|\1/\2|" | sed "s|^/||")
+                tag=$(classify "$file")
+                echo "- $tag REMOVED: \`$file\`"
+                ;;
+        esac
+    done
+    echo ""
+    echo "## Full Diff (truncated to first 2000 lines)"
+    echo ""
+    echo '```diff'
+    diff -ruN "$FROM_DIR" "$TO_DIR" | head -2000
+    echo '```'
+} > "$OUT"
+
+echo "Diff report written to: $OUT" >&2