Privacy Policy — DownDouyin

1. Overview & Scope

This Privacy Policy explains what information DownDouyin (https://downdouyin.com) processes when you use our web application to parse and download publicly accessible media from Douyin (抖音), how that information is used, and the choices available to you.

2. Media Streaming & Link Processing

• Submitted Video & Note Links: When you click Fetch Video or initiate a download, the Douyin share text or URL you paste is sent to our backend API (/api/parse, /api/proxy, /api/download, or /api/zip) solely to resolve metadata and stream the requested media file back to your browser.
• No Public Archive of Downloaded Media: Standard browser downloads (/api/proxy, /api/download, and /api/zip) stream through memory in real time and are not stored on our server disk after the transfer completes.
• Contact & Feedback Submissions: If you voluntarily submit a message through our Contact Form (/api/contact), your provided Name, Email, Category, Platform selection, and Message are recorded in our private server inbox log (logs/contact-messages.jsonl, with workflow state in logs/contact-state.json and anonymized funnel counters in logs/contact-events.jsonl). When transactional email notifications are enabled via Resend, a copy is dispatched to the site administrator and logged in logs/email-deliveries.jsonl.

3. Operational Server Logs, IP Handling & Retention

To monitor upstream CDN reliability, diagnose parsing failures, and protect the server from automated abuse, our backend records operational events in private server-side files under logs/ (including download-stats.jsonl, visitor-events.jsonl, activity-events.jsonl, visitors-index.json, app-errors.jsonl, and audit-log.jsonl):

• Download Statistics (logs/download-stats.jsonl): Records timestamp, random request ID (req_...), operation type (parse_request, file_download, or zip_download), platform name, download method, status, HTTP status code, generic error category, and transfer duration in milliseconds. Raw submitted URLs and IP addresses are not stored in download-stats.jsonl.
• Visitor & Activity Telemetry (visitor-events.jsonl, activity-events.jsonl, visitors-index.json): Records anonymous visitor/session IDs (vid_..., sid_...), device category, summarized browser/OS User-Agent, normalized source hostname and path preview (up to two sanitized path segments without query strings), a salted SHA-256 hash of the client IP (ip_...), and the client IP address formatted according to the administrator's configured ip_logging_mode (full, masked, or hashed; set to full by default to support abuse rate-limiting and IP blocking).
• Token & URL Redaction: Query strings and sensitive parameters (such as bearer tokens or session cookies) are stripped before operational logs and error summaries (app-errors.jsonl) are written.
• Log Size Caps & Retention Policy: JSONL log files automatically rotate/truncate when they reach their configured file-size ceiling (2 MB to 12 MB per file). In addition, the Admin Control Center provides configurable age-based retention pruning (defaulting to 90 days for operational logs and 365 days for contact messages) when retention cleanup is executed by the administrator.

4. Google Analytics 4 (GA4) & Privacy Redaction

DownDouyin uses Google Analytics 4 (Measurement ID: G-S9BHCYX6EN) to measure aggregate traffic and feature usage. Our client-side GA4 wrapper enforces strict parameter sanitization:

• Only generic, non-personal parameters (platform, download_method, status, and generic error_category) are sent to Google Analytics.
• Submitted video URLs, query strings, and cookies are never transmitted to Google Analytics.

5. Cookies & Browser Storage (localStorage)

DownDouyin uses first-party cookies and browser storage (localStorage and sessionStorage) for the following functional purposes:

• dd_theme & dd_lang (localStorage): Remembers your selected Light/Dark theme and interface language (English or 简体中文).
• dd_history_v2 (localStorage): Stores your recent local download history inside your own browser so you can revisit recent items; you can clear it at any time with a single click.
• dd_vid & dd_sid (first-party SameSite=Lax cookies and localStorage/sessionStorage): Random anonymous visitor ID (180-day expiry) and session ID (30-minute expiry) used to correlate parse requests with download completion metrics and prevent automated abuse.

For questions regarding this Privacy Policy or data requests, please contact us via our Contact & Support Page.