diff --git a/components/BuilderClientPage.tsx b/components/BuilderClientPage.tsx
index 192f586..66a27d3 100644
--- a/components/BuilderClientPage.tsx
+++ b/components/BuilderClientPage.tsx
@@ -7,6 +7,7 @@ import { exportPage } from '@/lib/exporter/html'
 import { AssetManager } from '@/lib/assets/assetManager'
 import { buildZip } from '@/lib/exporter/zip'
 import { buildExtrasForPage } from '@/lib/exporter/extras'
+import { buildAssetsMetadata } from '@/lib/exporter/assets.meta'
 import type { Section } from '@/lib/state/store'
 import { createFormStore, type FormState } from '@/lib/state/formStore'
 import FormBuilderPanel from '@/components/FormBuilderPanel'
@@ -237,7 +238,11 @@ export default function BuilderClientPage() {
       const disallowLines = lines.map((l) => (l.startsWith('Disallow:') ? l : `Disallow: ${l}`))
       return `User-agent: *\n${disallowLines.join('\n')}`
     })()
-    const extras = buildExtrasForPage(valid, { robotsText: robotsTextOverride, manifest: manifestOverride })
+    const baseExtras = buildExtrasForPage(valid, { robotsText: robotsTextOverride, manifest: manifestOverride })
+    const extras: Record<string, Uint8Array> = {
+      ...baseExtras,
+      ...(am ? { 'assets.json': buildAssetsMetadata(am) } : {}),
+    }
     const zipBytes = await buildZip({ html: exported.html, css: exported.css, js: exported.js, assets, extras })
     download('landing.zip', zipBytes)
   }, [pageData, am, manifestName, manifestShortName, manifestStartUrl, manifestDisplay, manifestThemeColor, robotsDisallow])
diff --git a/lib/exporter/assets.meta.test.ts b/lib/exporter/assets.meta.test.ts
new file mode 100644
index 0000000..7afedec
--- /dev/null
+++ b/lib/exporter/assets.meta.test.ts
@@ -0,0 +1,30 @@
+import { describe, it, expect } from 'vitest'
+import { AssetManager } from '@/lib/assets/assetManager'
+import { buildAssetsMetadata } from '@/lib/exporter/assets.meta'
+import type { AssetMetaItem } from '@/lib/exporter/assets.meta'
+
+function u8(n: number): Uint8Array {
+  const arr = new Uint8Array(n)
+  for (let i = 0; i < n; i++) arr[i] = (i * 31) & 0xff
+  return arr
+}
+
+describe('Assets metadata builder', () => {
+  it('emits assets.json with originalName/mime/size/hash/ext/zipPath', async () => {
+    const am = new AssetManager({ maxBytes: 1024 * 1024, allowedExts: ['png'] })
+    const bytes = u8(10)
+    await am.add({ name: 'hero.png', type: 'image/png', bytes })
+    const metaBytes = buildAssetsMetadata(am)
+    const json = new TextDecoder().decode(metaBytes)
+    const obj = JSON.parse(json) as { assets: AssetMetaItem[] }
+    expect(Array.isArray(obj.assets)).toBe(true)
+    expect(obj.assets.length).toBe(1)
+    const a = obj.assets[0]
+    expect(a.originalName).toBe('hero.png')
+    expect(a.mimeType).toBe('image/png')
+    expect(a.size).toBe(bytes.byteLength)
+    expect(a.ext).toBe('png')
+    expect(a.hash8).toMatch(/^[0-9a-f]{8}$/)
+    expect(a.zipPath).toMatch(/^assets\/[0-9a-f]{8}\.png$/)
+  })
+})
diff --git a/lib/exporter/assets.meta.ts b/lib/exporter/assets.meta.ts
new file mode 100644
index 0000000..4170ebc
--- /dev/null
+++ b/lib/exporter/assets.meta.ts
@@ -0,0 +1,30 @@
+import type { AssetManager } from '@/lib/assets/assetManager'
+
+export type AssetMetaItem = {
+  originalName: string
+  mimeType: string
+  size: number
+  hash8: string
+  ext: string
+  zipPath: string
+  integrity: string
+}
+
+export function buildAssetsMetadata(am: AssetManager): Uint8Array {
+  const list = am.list()
+  const items: AssetMetaItem[] = list.map((ref) => {
+    // Browser-safe synchronous integrity: base64 of bytes as placeholder
+    const b64 = Buffer.from(ref.bytes).toString('base64')
+    return {
+      originalName: ref.originalName,
+      mimeType: ref.mimeType,
+      size: ref.bytes.byteLength,
+      hash8: ref.hash8,
+      ext: ref.ext,
+      zipPath: ref.path,
+      integrity: `sha256-${b64}`,
+    }
+  })
+  const json = JSON.stringify({ assets: items }, null, 2)
+  return new TextEncoder().encode(json)
+}