diff --git a/TODO_NEXT_STEPS.txt b/TODO_NEXT_STEPS.txt
index 52c171a..4415009 100644
--- a/TODO_NEXT_STEPS.txt
+++ b/TODO_NEXT_STEPS.txt
@@ -4,6 +4,7 @@
 ================================================================================
 
 【已完成】
+   - V10.514 新增 Webcrumbs MOMO/PChome host data read-only API：`/api/webcrumbs/marketplace-host-data` 回傳與 `/webcrumbs` inline seed 相同的登入後 JSON contract，提供 plugin / QA / 其他專案 proxy 驗證；API boundary 明確標示不寫 DB、不呼叫 LLM、不抓外站，只允許 exact / total_price / price_alert_exact 價差摘要。
    - V10.513 外部工具診斷頁 payload 模組化：新增 `services/external_tool_payload_service.py`，把 Metabase/Grist/Webcrumbs 的診斷 payload 與 Webcrumbs host data 組裝移出 `routes/system_public_routes.py`，讓 route 回到 HTTP glue，`system_public_routes.py` 從 600+ 行降至 500 行內。
    - V10.512 Webcrumbs live plugin 接上 MOMO/PChome 只讀 host data：新增 `services/webcrumbs_host_data_service.py`，復用 `competitor_intel_repository.fetch_top_competitor_risks()` / coverage，把 exact / total_price / price_alert_exact 價差摘要轉成 `StockPlatformSharedUI.marketSnapshot` / `aiCandidate`；不呼叫 LLM、不抓外站、不寫 DB，無風險或失敗時仍輸出安全空狀態。
    - V10.511 Webcrumbs live plugin 補 host data 安全空狀態：`/webcrumbs` 會注入 `StockPlatformSharedUI.marketSnapshot` / `aiCandidate` 的診斷空資料，避免 plugin fallback demo 數字被誤認成真實市場或 AI 建議。
diff --git a/config.py b/config.py
index f259a50..b80f5be 100644
--- a/config.py
+++ b/config.py
@@ -402,7 +402,7 @@ YOUTUBE_API_KEY = os.getenv('YOUTUBE_API_KEY', '')
 # ==========================================
 # 系統版本與路徑
 # ==========================================
-SYSTEM_VERSION = "V10.513"
+SYSTEM_VERSION = "V10.514"
 LOG_FILE_PATH = os.path.join(BASE_DIR, 'logs/system.log')
 public_url = PUBLIC_URL  # 用於模板顯示
 
diff --git a/docs/guides/webcrumbs_shared_runtime.md b/docs/guides/webcrumbs_shared_runtime.md
index 8be10a2..91d0ee0 100644
--- a/docs/guides/webcrumbs_shared_runtime.md
+++ b/docs/guides/webcrumbs_shared_runtime.md
@@ -64,6 +64,7 @@ style.css
 
 - `/webcrumbs` 顯示 runtime URL、版本與 plugin base。
 - `/webcrumbs` 會嵌入同源 `/webcrumbs-assets/plugins/...` 的 live plugin preview，並由 momo-pro 注入只讀 MOMO/PChome exact 價差摘要；若資料源不可用或無風險候選，改注入診斷空狀態，避免 plugin fallback demo 數字在正式頁面被誤認成真實市場或 AI 建議。
+- `/api/webcrumbs/marketplace-host-data` 會回傳同一份登入後只讀 host data contract，供 plugin / QA / 其他專案 proxy 驗證；boundary 必須標示 `writes_database=false`、`calls_llm=false`、`fetches_external=false`。
 - `/webcrumbs-assets/loader/webcrumbs-compatible-loader.js` 回 200 且 content type 是 JavaScript。
 - `ewoooc_base.html` 在 `WEBCRUMBS_ENABLED=true` 且 runtime URL 有效時輸出 `<script data-webcrumbs-runtime=...>`。
 - 任一試點頁嵌入 plugin 後，瀏覽器 console 不應有 `MISSING_URI`、`STYLE_LOAD_ERROR`、`SCRIPT_LOAD_ERROR`。
diff --git a/docs/memory/history_logs.md b/docs/memory/history_logs.md
index 6b3c662..705e1aa 100644
--- a/docs/memory/history_logs.md
+++ b/docs/memory/history_logs.md
@@ -13,6 +13,7 @@
 ## 📅 詳細更新日誌 (考古存檔)
 
 ### 2026-05-31：Webcrumbs 共用 UI Runtime 與市場情報 writer approval
+- **V10.514 Webcrumbs host data read-only API**: 新增登入後 `/api/webcrumbs/marketplace-host-data`，回傳與 `/webcrumbs` inline seed 相同的 MOMO/PChome exact 價差 host data contract，供 plugin、QA 與其他專案 proxy 驗證；API boundary 明確標示 `writes_database=false`、`calls_llm=false`、`fetches_external=false`，且只允許 exact / total_price / price_alert_exact 摘要。
 - **V10.513 外部工具診斷 payload 模組化**: 新增 `services/external_tool_payload_service.py`，把 Metabase/Grist/Webcrumbs 診斷頁 payload 與 Webcrumbs host data 組裝從 `routes/system_public_routes.py` 移出；route 保持 HTTP glue 與 asset proxy，避免 Webcrumbs live plugin 與比價 host data 持續把公開系統 route 撐成大檔。
 - **V10.512 Webcrumbs MOMO/PChome host data**: 新增 `services/webcrumbs_host_data_service.py`，讓 `/webcrumbs` live plugin preview 復用 `competitor_intel_repository.fetch_top_competitor_risks()` 與 coverage，將 exact / total_price / price_alert_exact 的只讀價差摘要轉成 `StockPlatformSharedUI.marketSnapshot` / `aiCandidate`；不呼叫 LLM、不抓外站、不寫 DB，無風險或讀取失敗時仍輸出安全空狀態。
 - **V10.511 Webcrumbs host data 安全空狀態**: `/webcrumbs` 會注入 `StockPlatformSharedUI.marketSnapshot` / `aiCandidate` 的診斷空資料，避免 Shared UI Hub plugin 因資料源未接入而 fallback 顯示假市場數字、假 AI 候選或假信心分數。
diff --git a/routes/system_public_routes.py b/routes/system_public_routes.py
index f3bbe58..be7348b 100644
--- a/routes/system_public_routes.py
+++ b/routes/system_public_routes.py
@@ -12,7 +12,7 @@ import zipfile
 from datetime import datetime, timezone, timedelta
 from urllib.parse import quote
 
-from flask import Blueprint, Response, jsonify, render_template, send_from_directory, url_for
+from flask import Blueprint, Response, jsonify, render_template, request, send_from_directory, url_for
 import requests
 from sqlalchemy import text
 
@@ -26,7 +26,7 @@ from config import (
 )
 from database.manager import DatabaseManager
 from database.models import Product, PriceRecord
-from services.external_tool_payload_service import build_external_tool_payload
+from services.external_tool_payload_service import build_external_tool_payload, build_webcrumbs_seed_data
 from services.json_storage import load_categories
 from services.logger_manager import SystemLogger
 from utils.security import safe_join
@@ -108,6 +108,27 @@ def webcrumbs_status():
     )
 
 
+@system_public_bp.route('/api/webcrumbs/marketplace-host-data')
+@login_required
+def webcrumbs_marketplace_host_data_api():
+    """Read-only host data contract for Webcrumbs shared-ui plugins."""
+    limit = request.args.get('limit', 5, type=int) or 5
+    limit = max(1, min(limit, 8))
+    payload = build_webcrumbs_seed_data(limit=limit)
+    return jsonify({
+        'success': True,
+        'data': payload,
+        'metadata': payload.get('metadata') or {},
+        'boundary': {
+            'auth_required': True,
+            'writes_database': False,
+            'calls_llm': False,
+            'fetches_external': False,
+            'allowed_match_contract': 'exact/total_price/price_alert_exact',
+        },
+    })
+
+
 def _normalize_webcrumbs_asset_path(asset_path):
     candidate = (asset_path or '').strip().replace('\\', '/')
     normalized = posixpath.normpath(candidate).lstrip('/')
diff --git a/services/external_tool_payload_service.py b/services/external_tool_payload_service.py
index a682229..3aab9eb 100644
--- a/services/external_tool_payload_service.py
+++ b/services/external_tool_payload_service.py
@@ -62,9 +62,10 @@ def _is_blocked_external_url(configured_url):
     return parsed.scheme in {"http", "https"} and parsed.hostname != "mo.wooo.work"
 
 
-def _webcrumbs_seed_data():
+def build_webcrumbs_seed_data(limit: int = 5):
+    """Build safe Webcrumbs host data for page seed and read-only API."""
     try:
-        return build_webcrumbs_marketplace_host_data(limit=5)
+        return build_webcrumbs_marketplace_host_data(limit=limit)
     except Exception as exc:
         sys_log.warning(f"[Webcrumbs] host data build skipped: {exc}")
         return {
@@ -170,7 +171,7 @@ def _webcrumbs_payload():
         ],
         "plugin_previews": plugin_previews,
         "plugin_preview_uris": [preview["uri"] for preview in plugin_previews],
-        "plugin_seed_data": _webcrumbs_seed_data(),
+        "plugin_seed_data": build_webcrumbs_seed_data(limit=5),
     }
 
 
diff --git a/tests/test_external_tool_entrypoints.py b/tests/test_external_tool_entrypoints.py
index 23b0198..a2a78fb 100644
--- a/tests/test_external_tool_entrypoints.py
+++ b/tests/test_external_tool_entrypoints.py
@@ -39,9 +39,14 @@ def test_external_tool_bridge_pages_are_diagnostic_not_blank():
     assert "external-tool-diagnostics" in template
     assert "external-tool-action-grid" in template
     assert "def webcrumbs_status()" in route_source
+    assert "@system_public_bp.route('/api/webcrumbs/marketplace-host-data')" in route_source
+    assert "def webcrumbs_marketplace_host_data_api()" in route_source
+    assert "build_webcrumbs_seed_data(limit=limit)" in route_source
+    assert "'allowed_match_contract': 'exact/total_price/price_alert_exact'" in route_source
     assert "def webcrumbs_asset_proxy(asset_path)" in route_source
     assert "WEBCRUMBS_ASSET_ALLOWED_PREFIXES" in route_source
     assert "Webcrumbs 共用 UI Runtime" in service_source
+    assert "def build_webcrumbs_seed_data(limit: int = 5)" in service_source
     assert "build_webcrumbs_marketplace_host_data" in service_source
     assert "plugin_previews" in service_source
     assert "finance.market-ticker-strip/0.1.0" in service_source
diff --git a/tests/test_webcrumbs_host_data_service.py b/tests/test_webcrumbs_host_data_service.py
index 669a893..9d30abf 100644
--- a/tests/test_webcrumbs_host_data_service.py
+++ b/tests/test_webcrumbs_host_data_service.py
@@ -65,3 +65,19 @@ def test_webcrumbs_host_data_uses_empty_state_without_risks(monkeypatch):
     assert payload["marketSnapshot"][0]["freshness_status"] == "no_current_exact_risk"
     assert payload["aiCandidate"]["release_status"] == "blocked"
     assert "非同款、單位價或變體候選" in payload["aiCandidate"]["thesis"]
+
+
+def test_webcrumbs_seed_data_fallback_does_not_expose_demo_values(monkeypatch):
+    from services import external_tool_payload_service as payload_service
+
+    def boom(limit):
+        raise RuntimeError("db unavailable")
+
+    monkeypatch.setattr(payload_service, "build_webcrumbs_marketplace_host_data", boom)
+
+    payload = payload_service.build_webcrumbs_seed_data(limit=5)
+
+    assert payload["marketSnapshot"][0]["freshness_status"] == "diagnostic_unavailable"
+    assert payload["aiCandidate"]["release_status"] == "blocked"
+    assert "fallback demo" in payload["aiCandidate"]["thesis"]
+    assert "TAIEX" not in str(payload)