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FuckClaude - Open-source browser environment self-testing tool, will it be flagged by CC

Author: AI小集 · Original source: AI工具集

What is FuckClaude

FuckClaude is a lightweight, SEO-friendly, bilingual (Chinese and English) single-page browser detection tool used to scan a user's browser environment and determine whether it will be flagged by Claude Code as a "Chinese user". After clicking run, the tool performs scanning animations item by item, the score ring grows as risk accumulates, and finally gives a conclusion and a list of triggered signals. All detection is completed locally in the browser, without initiating any network requests or uploading any data.

FuckClaude

Main features of FuckClaude

  • Browser environment fingerprint scanning: One-click scanning of the local browser environment, using 6 signals (system time zone, browser language, installed Chinese fonts, Intl locale settings, time zone offset, Emoji rendering style) to comprehensively determine whether the user will be flagged by Claude Code as a "Chinese user".
  • Real-time risk scoring and visualization: Each signal outputs a 0–1 "China similarity" and multiplies it by a weight for accumulation, with a total score of 100, visually displaying low (0–30), medium (31–60), and high (61–100) risk levels through a dynamic score ring and scanning animation.
  • Local privacy protection: All detection is 100% completed locally in the browser, without initiating any network requests or uploading any user data, fully protecting privacy.
  • Detailed display of triggered signals: After scanning ends, a clear conclusion is given, and all "triggered" signals with scores ≥ 0.25 and their specific detection values are listed, helping users precisely locate the source of risk.
  • Bilingual Chinese and English interface: Built-in English (/) and Chinese (/zh/) bilingual support, automatically adapting to the user's language preference, and generating SEO-friendly sitemap and hreflang links,
  • Open source and deployable: Based on Astro 7.x static output, with no UI framework dependencies, it can be deployed with one click to any static hosting platform such as Cloudflare Pages, Vercel, Netlify, GitHub Pages.
  • Transparent and public technical principles: Based on public reverse engineering analysis of Claude Code's early relay fingerprinting behavior, it explains in detail detection mechanisms such as time zone steganographic encoding (date separator variants, Unicode apostrophe switching), for technical reference only.
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How to use FuckClaude

  • Use directly online: Open a browser and visit https://fuck-claude.app/（英文）或 https://fuck-claude.app/zh（中文），进入页面后点击扫描按钮即可一键启动检测。
  • View scan results: Wait for the item-by-item scanning animation to complete, observe the score ring changing in real time as risk accumulates, and finally view the risk level determination (low/medium/high) and the detailed list of all triggered signals.
  • Local development and deployment: After cloning the repository, run pnpm install to install dependencies, run pnpm dev to start the local development server (default address http://localhost:4321), use pnpm build to build static output to the dist/ directory, then use pnpm preview to preview the build result.
  • Custom domain deployment: Before deploying to static hosting platforms such as Cloudflare Pages, Vercel, Netlify, or GitHub Pages, replace the astro.config.mjs field and site in public/robots.txt with your real domain, ensuring that the canonical link,hreflang and the sitemap point correctly.
  • Switch language version: Use the language switch button on the page to freely switch between the English (/) and Chinese (/zh/) interfaces, and get the detection results and explanations in the corresponding language.
  • Understand the detection principles: Read the principle explanations at the bottom of the page to understand how each signal is detected and the weight logic, and make targeted adjustments to your browser environment settings (such as time zone, language, etc.) based on the items you trigger.

FuckClaude's official website address

  • Official website address：https://fuck-claude.app/
  • Github repository：https://github.com/LinXiaoTao/FuckClaude

FuckClaude's application scenarios

  • Self-check of the environment for Claude Code relay users: Developers or teams using unofficial API relay nodes (configured through ANTHROPIC_BASE_URL ), quickly check before connecting whether the local browser/system environment has the high-risk characteristics of being flagged as a "Chinese user" by Claude Code.
  • Browser fingerprinting technology research: Security researchers and reverse engineering enthusiasts study Claude Code's early proxy fingerprinting and steganographic encoding mechanisms (time zone mapping, date separator variants, Unicode apostrophe switching, etc.), as a technical reference case for browser fingerprint detection and anti-detection.
  • Privacy feature self-check: Privacy-sensitive users can, without exposing any data, use a 100% locally run scan to understand which "Chinese environment fingerprints" their browser leaks (time zone, language, installed fonts, etc.).
  • Verification of risk control bypass effectiveness: Operators using anti-fingerprinting tools such as the Roxy browser or multi-account isolation environments verify whether the current environment has successfully blocked low-level fingerprints such as Canvas, WebGL, and time zone, reducing the probability of being blocked by AI platform risk control.