Costook Privacy Policy
Last updated: October 8, 2026
Costook is a local-first bookkeeping application. This policy explains how information is handled when you use Costook.
1. Developer and scope
Costook is provided by Shanghai Mangzhu Information Technology Co., Ltd. (“we”, “us”, or “our”).
For privacy questions, contact us at mangzhutech@gmail.com. This policy applies to the Costook Android application and its related support pages.
2. Information stored on your device
Costook stores the information you enter or import, including books, transactions, accounts, assets, categories, budgets, notes, attachments, and preferences. This information is stored locally on your device.
Costook does not upload this local bookkeeping content to our servers. We do not operate an account system, cloud synchronization service, or remote backup service for this application.
3. Advertising, crash diagnostics, and remote configuration
Costook uses Google AdMob to display ads after you accept this policy. Google Mobile Ads may process device and advertising identifiers, IP address, diagnostic information, and ad interaction data to deliver, secure, measure, and personalize ads as permitted by your choices and applicable law. Google acts under its own privacy terms.
Google may process information through the Google Mobile Ads SDK as an independent provider. See Google's Advertising Privacy & Terms and Google's Privacy Policy. The exact data handling can depend on your device, region, consent choices, and the SDK version included in the released application.
After you accept this policy, Costook also initializes the following Firebase services on Android:
- Firebase Crashlytics helps us diagnose crashes and improve application stability. Crash reports may include exception messages, stack traces, relevant application state, application and operating-system versions, device metadata, and installation or session identifiers used by Firebase. Reports may be stored temporarily on your device and sent to Firebase when a network connection is available. We can view diagnostic reports in the Firebase console to investigate failures.
- Firebase Remote Config retrieves runtime configuration, including whether advertising is enabled. Requests may include a Firebase installation identifier and technical information about the application and device. Configuration is cached on your device for use on a later application start. The advertisement enablement setting is disabled by default when no configuration is available. Remote configuration does not provide cloud storage or synchronization of your bookkeeping data.
Costook does not use these services to upload your books, transactions, accounts, assets, budgets, notes, or attachments. We do not intentionally attach bookkeeping content, images, business logs, or a personal account identifier to crash reports. We do not integrate the Firebase Analytics SDK or report bookkeeping activities for advertising or behavioral analytics. Technical diagnostic information described above is still sent to Firebase.
Google processes Firebase service data as described in Firebase Privacy and Security and Google's Privacy Policy. The data processed may vary with the SDK version and service configuration. Advertising and Firebase data may be processed outside your country or region under Google's applicable terms and safeguards.
Costook does not provide accounts, cloud sync, remote backup, membership, payments, automatic bookkeeping, or online feedback. Advertising, crash diagnostics, and remote configuration do not upload your local bookkeeping content to our servers. If an advertisement or Firebase service is unavailable, bookkeeping features remain available.
4. Permissions
Costook requests a system permission only when you use the related local feature, such as selecting files or photos, or adding a system shortcut. The selected content is processed locally.
Permissions are not, by themselves, evidence that Costook uploads the selected files or photos. Costook does not receive your local bookkeeping content through the advertising SDK.
5. Your control, retention, and deletion
You can edit, export, or delete local data from within the app. Local data remains on your device until you delete it, clear the app's data, or uninstall the app. Uninstalling the app or clearing its data may permanently remove data that has not been exported.
Ad-related data handled by Google is retained and deleted according to Google's policies and controls. We do not have access to delete data held by Google; use Google's privacy controls or contact Google for those requests.
Crash diagnostics and Firebase installation or session data are retained according to the applicable Firebase service policies. Uninstalling Costook does not automatically delete reports already sent to Firebase. For privacy requests concerning Firebase data used by Costook, contact us at the address in this policy. Remote configuration cached on your device is removed when you clear the app's data or uninstall the app.
Keep exported files secure. If you contact us, we retain the message and contact details only as long as needed to respond, handle a legal request, or maintain support records, unless a longer period is required by law.
6. Security
Protect your device, operating-system account, application lock, and exported files. No storage method is completely risk-free, and you are responsible for maintaining backups of important data.
7. Children
Costook is not directed to children under the age required by applicable law. We do not knowingly collect personal information directly from children. If you believe a child has provided personal information to us, contact us at mangzhutech@gmail.com.
8. Policy changes
We may update this policy when Costook changes. The updated version will be included in a future app release and will show its effective date.
9. Contact
For privacy questions, contact mangzhutech@gmail.com. Please do not include sensitive bookkeeping data in a support request.