diff --git a/README.md b/README.md
index e3c3ab3..38b4eb9 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,7 @@ npm run dev
 
 Data files in `static/data/` are tracked in git. The only gitignored output is `scripts/output/minei.json` (33MB Chetyi-Minei source).
 
-**Data version**: `DATA_VERSION` in `src/ui/app.ts` controls cache invalidation. Bump it when restructuring data (new fields, reorganized bundles, updated sources) to force users to re-fetch cached data on next app load.
+**Data version**: derived automatically at build time from a content hash of `static/data/`, embedded as a `version` field in the preload manifest. Any data change (including edits to existing files) auto-invalidates cached data on the next app load — no manual bump required. Regenerate with `npm run generate-manifest` and commit the manifest with the data changes.
 
 **Preload manifest**: After adding or removing data files, regenerate the preload manifest:
 ```bash
diff --git a/README_RUS.md b/README_RUS.md
index ce484ba..cd36bfe 100644
--- a/README_RUS.md
+++ b/README_RUS.md
@@ -34,7 +34,7 @@ npm run dev
 
 Файлы данных в `static/data/` отслеживаются в git. Единственный игнорируемый файл вывода — `scripts/output/minei.json` (33МБ источник Четьи-Миней).
 
-**Версия данных**: `DATA_VERSION` в `src/ui/app.ts` управляет инвалидацией кэша. Увеличивайте её при реструктуризации данных (новые поля, перегруппированные пачки, обновлённые источники), чтобы пользователи получили свежие данные при следующей загрузке приложения.
+**Версия данных**: вычисляется автоматически при сборке как хеш содержимого `static/data/` и записывается в поле `version` манифеста предзагрузки. Любое изменение данных (включая правку существующих файлов) автоматически инвалидирует кэш при следующей загрузке приложения — ручное увеличение версии не требуется. Перегенерируйте через `npm run generate-manifest` и закоммитьте манифест вместе с изменениями данных.
 
 **Манифест предзагрузки**: После добавления или удаления файлов данных перегенерируйте манифест:
 ```bash
diff --git a/scripts/generate-preload-manifest.ts b/scripts/generate-preload-manifest.ts
index 3944de9..d088dab 100644
--- a/scripts/generate-preload-manifest.ts
+++ b/scripts/generate-preload-manifest.ts
@@ -7,19 +7,20 @@
 
 import * as fs from 'fs';
 import * as path from 'path';
+import { createHash } from 'crypto';
 import { fileURLToPath } from 'url';
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
 const DATA_DIR = path.resolve(__dirname, '../static/data');
-const LANGUAGES = ['en', 'ru', 'cu'];
+const LANGUAGES = ['en', 'ru', 'cu'] as const;
 const dom = [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
 
 interface Manifest {
-  [lang: string]: {
-    calendar: string[];
-    bible: string[];
-  };
+  version?: string;
+  en?: { calendar: string[]; bible: string[] };
+  ru?: { calendar: string[]; bible: string[] };
+  cu?: { calendar: string[]; bible: string[] };
 }
 
 function exists(p: string): boolean {
@@ -208,16 +209,53 @@ function calendarFiles(lang: string): string[] {
   return files;
 }
 
-const manifest: Manifest = {} as Manifest;
+const manifest: Manifest = {};
 
 for (const lang of LANGUAGES) {
   manifest[lang] = {
     calendar: calendarFiles(lang),
     bible: ['/data/bible/versions.json'],
   };
-  console.log(`${lang}: ${manifest[lang].calendar.length} calendar files`);
+  console.log(`${lang}: ${manifest[lang]!.calendar.length} calendar files`);
 }
 
 const outPath = path.join(DATA_DIR, 'shared', 'preload-manifest.json');
+
+/**
+ * SHA-256 content hash over the data tree (relative path + bytes, sorted),
+ * truncated to 12 hex chars. The manifest itself is excluded so regenerating
+ * it cannot change its own version. Used by the runtime to invalidate the
+ * IndexedDB cache whenever any data file changes.
+ */
+function computeDataVersion(dataDir: string, excludePath: string): string {
+  const hash = createHash('sha256');
+  const files: string[] = [];
+  const walk = (dir: string): void => {
+    const entries = fs.readdirSync(dir, { withFileTypes: true })
+      .filter((e) => !e.name.startsWith('.'))
+      .sort((a, b) => (a.name < b.name ? -1 : a.name > b.name ? 1 : 0));
+    for (const entry of entries) {
+      const full = path.join(dir, entry.name);
+      if (entry.isDirectory()) walk(full);
+      else if (entry.isFile()) files.push(full);
+    }
+  };
+  walk(dataDir);
+  files.sort((a, b) => (a < b ? -1 : a > b ? 1 : 0));
+  const excludeAbs = path.resolve(excludePath);
+  for (const file of files) {
+    if (path.resolve(file) === excludeAbs) continue; // exclude the manifest itself (avoids self-reference)
+    const rel = path.relative(dataDir, file).split(path.sep).join('/');
+    hash.update(rel);
+    hash.update('\0');
+    hash.update(fs.readFileSync(file));
+    hash.update('\0');
+  }
+  return hash.digest('hex').slice(0, 12);
+}
+
+const version = computeDataVersion(DATA_DIR, outPath);
+manifest.version = version;
+console.log(`\nData version: ${version}`);
 fs.writeFileSync(outPath, JSON.stringify(manifest, null, 2));
-console.log(`\nManifest written to ${outPath}`);
\ No newline at end of file
+console.log(`\nManifest written to ${outPath}`);
diff --git a/src/ui/app.ts b/src/ui/app.ts
index a048345..de820cd 100644
--- a/src/ui/app.ts
+++ b/src/ui/app.ts
@@ -76,8 +76,19 @@ export class App {
   }
 
   private async checkDataVersion() {
-    const DATA_VERSION = '2026-08-04'; // bump when data structure changes
     try {
+      // Data version is derived at build time from a content hash of the data
+      // tree, embedded in the preload manifest (scripts/generate-preload-manifest.ts).
+      // Reading it here means any data change auto-invalidates cached data —
+      // no hand-maintained constant to forget to bump.
+      const manifest = await DataCache.fetchWithFallback<{ version?: string }>('/data/shared/preload-manifest.json');
+      const dataVersion = manifest?.version;
+      if (typeof dataVersion !== 'string' || dataVersion.length === 0) {
+        // No manifest/version (offline first run, or a stale deployment) —
+        // can't determine staleness; never wipe the cache on an unreadable signal.
+        diagLog('version-check', { result: 'no-version', action: 'skip' });
+        return;
+      }
       const present = await DataCache.has('__data_version__');
       if (present === null) {
         // Unreadable IDB — never wipe the cache on a flaky read
@@ -85,15 +96,15 @@ export class App {
         return;
       }
       if (!present) {
-        await DataCache.set('__data_version__', DATA_VERSION);
-        diagLog('version-init');
+        await DataCache.set('__data_version__', dataVersion);
+        diagLog('version-init', { version: dataVersion });
         return;
       }
       const cachedVer = await DataCache.get('__data_version__') as string | null;
-      if (cachedVer !== DATA_VERSION) {
+      if (cachedVer !== dataVersion) {
         await DataCache.clear();
-        await DataCache.set('__data_version__', DATA_VERSION);
-        diagLog('version-clear', { old: cachedVer });
+        await DataCache.set('__data_version__', dataVersion);
+        diagLog('version-clear', { old: cachedVer, version: dataVersion });
       }
     } catch (err) {
       diagLog('idb-error', { where: 'checkDataVersion', msg: String(err) });
@@ -106,7 +117,7 @@ export class App {
     this.handleRoute();
     window.addEventListener('hashchange', () => this.handleRoute());
 
-    // Data version check — bump DATA_VERSION when static data structure changes
+    // Data version check — the version comes from the preload manifest's content hash; run `npm run generate-manifest` after data changes
     this.checkDataVersion();
 
     // Close dropdown menus on click/touch outside
diff --git a/static/data/shared/preload-manifest.json b/static/data/shared/preload-manifest.json
index 10ac975..5cbbe1d 100644
--- a/static/data/shared/preload-manifest.json
+++ b/static/data/shared/preload-manifest.json
@@ -5260,5 +5260,6 @@
     "bible": [
       "/data/bible/versions.json"
     ]
-  }
+  },
+  "version": "7631e35da99e"
 }
\ No newline at end of file