diff --git a/package-lock.json b/package-lock.json
index e13a3f0..9ff7891 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1714,9 +1714,9 @@
       "license": "MIT"
     },
     "node_modules/fast-uri": {
-      "version": "3.1.5",
-      "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.5.tgz",
-      "integrity": "sha512-gHwA1O9LDIcKunMKhObS/HimwtehO1nPUECKAu5TpKgaO19fcWEl4bliWe1jWxVFvIXztJjjQ4L8XQ1EU9f7Jw==",
+      "version": "3.1.7",
+      "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.7.tgz",
+      "integrity": "sha512-dOvZVzjdZdz7phd9v6jCbwxrBW3fK6n8Rc0CtdmM4bumzMnxywBYhuph6J819RRw/ku+rLbelwfMunktuzVVHg==",
       "dev": true,
       "funding": [
         {
diff --git a/package.json b/package.json
index dabe983..bb8c9f3 100644
--- a/package.json
+++ b/package.json
@@ -16,8 +16,9 @@
     "build:mac": "electron-builder --mac",
     "build:linux": "electron-builder --linux",
     "check-version": "node build-version.js",
-    "update-elemco-options": "node scripts/parse-elemco-options.js",
-    "update-elemco-macros": "node scripts/parse-elemco-macros.js",
+    "update-elemco-options": "node scripts/parse-elemco-options.js && node scripts/check-elemco-sync.js",
+    "update-elemco-macros": "node scripts/parse-elemco-macros.js && node scripts/check-elemco-sync.js",
+    "check-elemco-sync": "node scripts/check-elemco-sync.js",
     "smoke": "electron . --smoke --disable-gpu",
     "start-debug:win": "node_modules/electron/dist/electron.exe . --enable-logging=file --log-file=jlmol-debug.log --log-level=0"
   },
diff --git a/scripts/check-elemco-sync.js b/scripts/check-elemco-sync.js
new file mode 100644
index 0000000..caa800e
--- /dev/null
+++ b/scripts/check-elemco-sync.js
@@ -0,0 +1,122 @@
+#!/usr/bin/env node
+
+/**
+ * Cross-check the hand-curated method registry (js/elemco-methods.js) against
+ * the generated ElemCo.jl catalogs (js/elemco-macros.js, js/elemco-options.js).
+ *
+ * The registry is deliberately hand-maintained, so it can silently drift from
+ * the backend: a registry entry can point at a macro or option group that no
+ * longer exists in the pinned ElemCo version, and new backend macros can stay
+ * unreachable from the UI without anyone noticing. This script makes the drift
+ * loud:
+ *
+ *   errors (exit 1):
+ *     - a registry macro missing from ELEMCO_MACROS
+ *     - a referenced option group (per-method `groups`, ELEMCO_GLOBAL_GROUPS,
+ *       ELEMCO_GLOBAL_EXCLUDE) missing from ELEMCO_OPTIONS
+ *     - an ELEMCO_GLOBAL_EXCLUDE field missing from its group
+ *     - the two generated catalogs pinned to different ElemCo versions
+ *
+ *   warnings (informational):
+ *     - catalog macros not covered by any registry entry (curation candidates)
+ *
+ * Usage:
+ *   node scripts/check-elemco-sync.js
+ *   npm run check-elemco-sync
+ */
+
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const vm = require('vm');
+
+const JS_DIR = path.join(__dirname, '..', 'js');
+
+// The catalog files assign to `window.*`; elemco-methods.js declares consts and
+// copies them onto `window` when present. Run all three in one sandboxed
+// context whose only global is a fake `window`, and read everything back from
+// it -- nothing here needs this process's globals, so nothing gets them.
+const context = vm.createContext({ window: {} });
+for (const f of ['elemco-macros.js', 'elemco-options.js', 'elemco-methods.js']) {
+  vm.runInContext(fs.readFileSync(path.join(JS_DIR, f), 'utf8'), context, { filename: f });
+}
+const w = context.window;
+
+const errors = [];
+const warnings = [];
+
+// ---- catalog version pins must agree -----------------------------------------
+if (w.ELEMCO_MACROS.sourceRef !== w.ELEMCO_OPTIONS.sourceRef) {
+  errors.push(
+    `catalog version mismatch: elemco-macros.js @ ${w.ELEMCO_MACROS.sourceRef}, ` +
+    `elemco-options.js @ ${w.ELEMCO_OPTIONS.sourceRef} — regenerate both with the same --ref`
+  );
+}
+
+// ---- every registry macro must exist in the macros catalog -------------------
+const catalogMacros = new Set(w.ELEMCO_MACROS.macros.map((m) => m.name));
+const registryEntries = [
+  ...(w.ELEMCO_METHODS.reference || []).map((m) => ({ where: `reference/${m.id}`, macro: m.macro, groups: m.groups })),
+  ...w.ELEMCO_CORRELATION_GROUPS.flatMap((g) =>
+    g.methods.map((m) => ({ where: `${g.group}/${m.id}`, macro: m.macro, groups: m.groups }))),
+];
+const usedMacros = new Set();
+for (const e of registryEntries) {
+  const name = (e.macro || '').replace(/^@/, '');
+  usedMacros.add(name);
+  if (!catalogMacros.has(name)) {
+    errors.push(`${e.where}: macro ${e.macro} not in elemco-macros.js (${w.ELEMCO_MACROS.sourceRef})`);
+  }
+}
+
+// ---- every referenced option group must exist in the options catalog ---------
+const catalogGroups = w.ELEMCO_OPTIONS.groups;
+const checkGroup = (where, gid) => {
+  if (!catalogGroups[gid]) {
+    errors.push(`${where}: option group '${gid}' not in elemco-options.js (${w.ELEMCO_OPTIONS.sourceRef})`);
+  }
+};
+for (const e of registryEntries) (e.groups || []).forEach((gid) => checkGroup(e.where, gid));
+(w.ELEMCO_GLOBAL_GROUPS || []).forEach((gid) => checkGroup('ELEMCO_GLOBAL_GROUPS', gid));
+for (const [gid, fields] of Object.entries(w.ELEMCO_GLOBAL_EXCLUDE || {})) {
+  checkGroup('ELEMCO_GLOBAL_EXCLUDE', gid);
+  // Catalog groups keep their options under `fields` (see parse-elemco-options.js).
+  const known = catalogGroups[gid] ? catalogGroups[gid].fields : null;
+  for (const f of fields) {
+    if (known && !known[f]) {
+      errors.push(`ELEMCO_GLOBAL_EXCLUDE: field '${gid}.${f}' not in elemco-options.js (${w.ELEMCO_OPTIONS.sourceRef})`);
+    }
+  }
+}
+
+// ---- reverse direction: catalog macros the registry does not surface ---------
+// Utility/IO macros are legitimately absent from the method registry; list the
+// rest as curation candidates so a new backend method cannot stay invisible.
+const UTILITY = new Set([
+  'check_molproinfo', 'copyfile', 'copywf', 'deletefile', 'dummy', 'export_molden',
+  'dfints', 'ints', 'moints', 'transform_ints', 'write_ints', 'import_matrix',
+  'freeze_orbs', 'rotate_orbs', 'show_orbs', 'localize', 'region', 'loadfile',
+  'loadwf', 'savefile', 'savewf', 'usewf', 'molpro_input', 'molpro_output',
+  'opt', 'reset', 'run', 'set', 'set_default_eltype',
+]);
+for (const m of w.ELEMCO_MACROS.macros) {
+  if (usedMacros.has(m.name) || UTILITY.has(m.name)) continue;
+  // Documented aliases of a surfaced macro are covered by the original.
+  const alias = /^Alias for @(\S+?)\.?(?:\s|$)/.exec(m.doc || '');
+  if (alias && usedMacros.has(alias[1])) continue;
+  warnings.push(`macro @${m.name} is in elemco-macros.js but not surfaced by the method registry`);
+}
+
+// ---- report ------------------------------------------------------------------
+for (const m of warnings) console.warn(`warning: ${m}`);
+if (errors.length) {
+  for (const m of errors) console.error(`ERROR: ${m}`);
+  console.error(`\ncheck-elemco-sync: ${errors.length} error(s), ${warnings.length} warning(s)`);
+  process.exit(1);
+}
+console.log(
+  `check-elemco-sync: OK — ${registryEntries.length} registry entries against ` +
+  `${catalogMacros.size} macros / ${Object.keys(catalogGroups).length} option groups ` +
+  `@ ${w.ELEMCO_OPTIONS.sourceRef}${warnings.length ? `, ${warnings.length} warning(s)` : ''}`
+);