Privacy Policy

1. Scope

Fu-Sen is a Chrome extension that helps users understand selected text on webpages and PDFs by providing AI-generated explanations.

Fu-Sen is designed so that much of your reading history, saved explanations, and notes remain on your own device rather than being stored in Fu-Sen’s servers.

This Privacy Policy applies to information processed through:

• the Fu-Sen Chrome extension;
• fu-sen.app and related webpages;
• Fu-Sen’s backend services; and
• third-party services used to provide Fu-Sen, such as Cloudflare, OpenAI, and Google.

2. Information We Process

The information processed by Fu-Sen falls into several categories depending on how you use the Service and where the information is stored.

2.1 Information Stored Locally on Your Device

The following information may be stored in your Chrome profile using storage available to the Fu-Sen extension:

• the webpage URL and page title associated with content you save;
• text you selected for explanation;
• surrounding text or context associated with the selected text;
• information used to locate the selected text again when you revisit the page;
• AI-generated explanations;
• follow-up questions and related conversation history;
• notes you create;
• display and feature settings, such as language, text size, auto-save, revisit behavior, Web Search settings, and PDF-related settings; and
• certain authentication and installation credentials stored in extension-only storage that is not exposed to the webpages you visit.

Saved explanations, notes, and related page information are not stored in Fu-Sen’s application database.

Local explanations and notes are not separated by Google account. If you log out of one Google account and later sign in with another Google account using the same Chrome profile, locally stored explanations and notes may still be visible.

Logging out of Fu-Sen does not automatically delete this local content.

You can delete locally stored explanations and notes through Fu-Sen’s interface. Local data may also be deleted as part of the account deletion process described below or when the extension is uninstalled.

2.2 Information Sent When You Use AI Features

Fu-Sen does not continuously transmit the contents of webpages you visit.

Information is transmitted for AI processing only when you take an action that requests an AI feature, such as requesting an explanation, regenerating an explanation, asking a follow-up question, or requesting a re-explanation.

Depending on the feature you use, the transmitted information may include:

• the text you selected;
• surrounding text necessary to understand the selected passage;
• the webpage URL;
• the webpage title;
• the requested explanation type or feature;
• your language setting;
• whether Web Search is enabled; and
• for follow-up questions or re-explanations, relevant portions of the existing explanation, quoted text, and related conversation history.

Notes you create in Fu-Sen are not included in AI requests.

Fu-Sen does not intentionally transmit the contents of unrelated portions of a webpage that you have not selected or otherwise used as part of an AI request.

Fu-Sen does not store the selected text, surrounding context, AI-generated explanation, or conversation content in its application database after the AI request has been processed.

2.3 Account and Authentication Information

If you choose to sign in with Google, Fu-Sen may process:

• your Google account email address; and
• a unique account identifier provided by Google.

Fu-Sen requests only the Google permissions needed to confirm your identity and obtain your email address, currently including openid and userinfo.email.

A Google access token may be used temporarily to verify your identity. Fu-Sen does not store the Google access token as a persistent account record.

Fu-Sen may also process:

• Fu-Sen account identifiers;
• installation identifiers;
• authentication status;
• hashed session identifiers;
• your Fu-Sen plan;
• usage limits;
• token usage;
• timestamps associated with account or usage activity; and
• information necessary to determine Guest eligibility or prevent repeated abuse of free usage.

Fu-Sen stores a hash of a session token rather than the session token itself on its servers.

2.4 Guest and Anti-Abuse Information

If you use Fu-Sen as a Guest or begin a Guest session, Fu-Sen may process:

• an installation identifier;
• information necessary to establish Guest eligibility;
• usage associated with that installation;
• verification results generated through Cloudflare Turnstile; and
• technical information reasonably necessary to prevent bots, automated abuse, excessive use, or circumvention of usage limits.

2.5 Technical and Log Information

When your browser communicates with Fu-Sen’s servers, certain technical information may be processed automatically, including:

• IP address;
• date and time of requests;
• browser information;
• extension version;
• request status;
• security-related metadata; and
• information necessary to diagnose errors or prevent abuse.

Fu-Sen is configured not to intentionally write AI prompt text, AI response text, authentication secrets, or other unnecessary sensitive content to its application logs.

2.6 PDF Content

Fu-Sen may detect and display PDFs through its dedicated PDF viewer.

The PDF file itself is processed locally on your device for viewing and text selection and is not uploaded in full to Fu-Sen’s servers.

If you select text within a PDF and request an AI explanation, only the information necessary for that AI request is transmitted as described in Section 2.2.

2.7 Support Information

If you contact us by email or another support channel, we may receive the information you choose to provide, such as:

• your email address;
• the content of your message;
• screenshots or diagnostic information you voluntarily provide; and
• other information necessary to respond to your request.

Please do not send passwords, authentication tokens, or unnecessary sensitive information in support requests.

3. How We Use Information

We use information processed through the Service only as reasonably necessary to:

• provide AI-generated explanations and related features;
• provide Web Search-assisted explanations when you choose to use that functionality;
• authenticate users through Google;
• establish and manage Guest access;
• maintain accounts and sessions;
• enforce usage limits;
• display usage information;
• detect, investigate, and prevent fraud, bots, abuse, security incidents, and violations of our Terms;
• operate, maintain, secure, and troubleshoot the Service;
• respond to support requests;
• process account deletion and privacy requests;
• understand aggregated service performance and improve the Service; and
• comply with applicable law.

We do not use selected text, AI conversations, or your saved notes to build advertising profiles.

We do not use your information to determine creditworthiness.

We do not use your information for targeted advertising.

We do not sell personal information.

We do not share personal information for cross-context behavioral advertising.

We do not use content submitted through Fu-Sen to train our own general-purpose AI models.

4. AI Processing

Fu-Sen uses OpenAI services to generate AI explanations and, when enabled, provide Web Search-assisted responses.

AI requests are sent from the Fu-Sen extension to Fu-Sen’s backend infrastructure and then transmitted through Cloudflare infrastructure to OpenAI.

Fu-Sen does not store the text submitted for AI processing or the resulting AI response in its own application database after processing.

However, third-party AI providers may temporarily process or retain API data in accordance with their own applicable terms, privacy policies, security practices, and data retention rules. For example, an AI provider may temporarily retain limited API data for abuse monitoring, security, or legal compliance.

OpenAI states that data submitted through its API is not used to train or improve its models unless the API customer explicitly opts in to such data sharing.

Fu-Sen does not intentionally opt users’ AI content into model-training data sharing.

Because third-party provider practices may change over time, their current policies govern their own processing of information.

5. Service Providers

We use third-party service providers to operate the Service.

Cloudflare

Cloudflare may provide services including:

• Cloudflare Workers;
• Cloudflare D1;
• Cloudflare AI Gateway;
• Cloudflare Turnstile;
• security and anti-abuse services; and
• Cloudflare Web Analytics.

Cloudflare may process account information, usage information, request metadata, technical information, and information transmitted through Fu-Sen’s backend where necessary to provide these services.

OpenAI

OpenAI provides AI processing used to generate explanations and may provide Web Search functionality used as part of those explanations.

Information described in Section 2.2 may be transmitted to OpenAI when you request an AI feature.

Google

Google provides authentication services used when you choose to sign in with your Google account.

Fu-Sen receives only the account information necessary for authentication as described in Section 2.3.

We may also disclose information to a service provider that replaces one of the providers listed above, but only where reasonably necessary to provide the Service and subject to appropriate privacy and security protections.

6. Website Analytics and Cookies

We may use Cloudflare Web Analytics to understand aggregated traffic and performance information relating to the Fu-Sen website.

Cloudflare describes Web Analytics as a privacy-focused analytics service that does not collect or use visitors’ personal data and does not track individual users across customers’ websites.

Fu-Sen does not use website analytics for behavioral advertising.

Cloudflare Turnstile and other security or authentication mechanisms may use necessary browser technologies or signals to distinguish legitimate users from automated traffic and to protect the Service.

We do not use advertising cookies.

7. Data Retention

We retain personal information only for as long as reasonably necessary for the purpose for which it is processed, unless a longer period is required by law.

Our general retention practices are as follows:

• Locally stored explanations, notes, page information, and conversation history: stored in your Chrome profile until you delete them, delete your account where applicable, reset relevant extension data, or uninstall the extension.
• Account information, including email address, Google account identifier, plan information, and account usage information: retained while your Fu-Sen account exists and deleted when the account is deleted, except for information we are required or permitted to retain for security, fraud prevention, legal compliance, or other legitimate purposes.
• Fu-Sen sessions: valid for no longer than 30 days.
• Re-registration prevention record: a keyed or otherwise protected hash derived from the Google account identifier may be retained for up to 168 hours (7 days) after account deletion.
• Account deletion completion record: information necessary to confirm the result of an account deletion request may be retained for up to 168 hours (7 days), after which it is deleted through an automated process.
• Server and security logs: generally retained for up to 12 months, unless a shorter period is sufficient or a longer period is reasonably necessary for security, abuse investigation, or legal compliance.
• AI request and response content in Fu-Sen’s application database: not stored.
• Support communications: retained as reasonably necessary to respond to your request, maintain support records, resolve disputes, or protect the Service.

Third-party service providers may maintain their own retention periods under their respective policies.

We may retain aggregated or de-identified information that cannot reasonably be linked to an individual where permitted by law.

8. Account Deletion

You may delete your Fu-Sen account through the functionality provided by Fu-Sen, subject to identity verification where necessary.

When your account is deleted:

• account authentication information associated with that account is deleted from Fu-Sen’s servers;
• plan and usage information associated with the account is deleted, subject to any information that must be retained for security or legal purposes;
• locally stored explanations, notes, and conversation history in the Chrome profile from which you perform the deletion may be deleted;
• local content is not separated by Google account, so deleting local content from that Chrome profile may also remove content created while another Google account was signed in;
• a protected hash derived from your Google account identifier may be retained for up to 168 hours to enforce a temporary re-registration restriction; and
• certain installation-level Guest eligibility or anti-abuse information and extension settings may remain where necessary for service integrity or Guest eligibility management.

Account deletion cannot be undone.

Uninstalling the Fu-Sen extension removes extension data stored by Chrome in accordance with Chrome’s extension storage behavior, but it does not by itself constitute a request to delete server-side account data.

9. Your U.S. Privacy Rights

Depending on your state of residence and whether applicable privacy law applies to Fu-Sen, you may have rights regarding your personal information, including the right to:

• request information about the personal information we collect, use, or disclose;
• request access to personal information we maintain about you;
• request correction of inaccurate personal information;
• request deletion of personal information;
• obtain a portable copy of certain personal information;
• opt out of certain sales, sharing, targeted advertising, or profiling where applicable;
• appeal a decision regarding a privacy request where required by applicable law; and
• exercise applicable privacy rights without unlawful discrimination.

Fu-Sen does not sell personal information or share personal information for cross-context behavioral advertising or targeted advertising.

To exercise an applicable privacy right, email:

hello@fu-sen.app

Please describe your request and provide enough information for us to identify the relevant account or data.

We may ask you to verify your identity before acting on a request.

Privacy requests are provided without charge except where applicable law permits a fee for requests that are manifestly unfounded, excessive, or repetitive.

Information stored only on your device may not be accessible to us. Where applicable, you can view or delete that information directly through Fu-Sen or your Chrome extension data.

10. Sensitive and Confidential Information

Fu-Sen is designed as a general reading and learning tool and is not intended to process highly sensitive or regulated information.

Please do not submit sensitive or confidential information for AI processing unless you understand and accept that the information will be transmitted to the service providers described in this Privacy Policy.

In particular, you should avoid submitting:

• passwords or authentication credentials;
• financial account credentials;
• payment card numbers;
• Social Security numbers or other government identifiers;
• medical records or protected health information;
• highly sensitive employment or legal records;
• private communications belonging to another person; or
• confidential business or trade-secret information.

Fu-Sen is not a healthcare service and is not intended to be used as a system for processing protected health information.

11. Children’s Privacy

Fu-Sen is not directed to children under 13 years of age, and we do not knowingly collect personal information from children under 13.

If you are between 13 and 16 years old, you should use Fu-Sen only with the consent of your parent or legal guardian where such consent is required by applicable law.

If we learn that we have collected personal information from a child in violation of applicable law, we will take reasonable steps to delete the information.

A parent or legal guardian who believes that a child has provided personal information to Fu-Sen may contact us at:

hello@fu-sen.app

12. Data Security

We use reasonable technical and organizational safeguards designed to protect information processed through Fu-Sen.

These measures include, as applicable:

• encrypted HTTPS/TLS connections;
• keeping OpenAI API keys and other backend credentials on server-side infrastructure rather than distributing them in the extension;
• storing authentication credentials in extension-only storage that is not made available to webpages;
• storing server-side session identifiers as hashes rather than storing raw session tokens;
• limiting the information stored in Fu-Sen’s backend database;
• avoiding intentional storage of AI prompt and response content in Fu-Sen’s application database;
• avoiding intentional logging of AI prompt and response content in Fu-Sen application logs; and
• limiting access to infrastructure and credentials according to operational need.

No method of transmission, processing, or storage is completely secure, and we cannot guarantee absolute security.

13. International Processing

Fu-Sen is operated from Japan.

Some of the service providers we use, including Cloudflare, OpenAI, and Google, are based in or operate infrastructure in the United States and other countries.

As a result, information may be processed in Japan, the United States, or another country in which a service provider operates.

Privacy and data protection laws may differ between countries.

We use third-party providers only where reasonably necessary to provide, secure, or operate the Service.

14. Google API Data

Fu-Sen uses Google account information only for authentication and account management as described in this Privacy Policy.

Fu-Sen’s use and transfer of information received from Google APIs will adhere to the applicable Google API Services User Data Policy, including applicable Limited Use requirements.

Fu-Sen does not use information obtained from Google APIs for advertising, advertising profiles, credit decisions, or training generalized AI models.

15. Disclosure Required by Law and Business Transfers

We may disclose information where reasonably necessary to:

• comply with applicable law, regulation, legal process, or enforceable governmental request;
• protect the rights, safety, and security of Fu-Sen, our users, or others;
• investigate fraud, abuse, or security incidents; or
• establish, exercise, or defend legal claims.

If Fu-Sen or substantially all of its assets are transferred as part of a merger, acquisition, reorganization, or similar transaction, information may be transferred as part of that transaction subject to applicable law and appropriate privacy protections.

16. Changes to This Privacy Policy

We may update this Privacy Policy from time to time.

When we make changes, we will update the Effective Date shown at the top of this page.

If a change materially affects how we collect, use, or disclose personal information, we will provide reasonable notice where required by applicable law or where we determine that advance notice is appropriate.

Your continued use of the Service after an updated Privacy Policy becomes effective is subject to the updated Policy.

17. Contact Us

If you have questions, concerns, requests, or complaints regarding this Privacy Policy or the processing of your personal information, please contact:

Email: hello@fu-sen.app