Uwarp

Are you a Claude “China user”?

  • 100% local scan
  • Results never uploaded
  • Open source inspired
Claude China user check mascot sleeping, waiting for scan to start
0/ 100

Ready to scan

What gets scanned

Six locale fingerprints, weighted to a 0–100 risk score.

  • System timezoneClaude sameWeight 30

    Intl.DateTimeFormat exposes the same OS timezone Claude Code reads; compared against Asia/Shanghai, Asia/Urumqi and other China zones.

  • Browser languageWeight 24

    navigator.languages — zh-CN / Simplified Chinese at the top of the list scores highest.

  • Installed Chinese fontsWeight 20

    Canvas width-probing for Simplified / Traditional Chinese fonts such as Microsoft YaHei and PingFang SC.

  • Intl localeWeight 10

    The locale your browser resolves for date and number formatting.

  • Timezone offsetWeight 8

    Whether getTimezoneOffset() equals UTC+8.

  • Emoji rendering styleWeight 8

    OS vendor guessed from the user agent; a weak, loosely correlated signal.

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Are you a Claude "China user"?

One-click check of your browser timezone, language, Chinese fonts and locale to see if Claude Code would flag you as a China user. 100% local, nothing uploaded.

What is the Claude China user check?

This hosted scanner replicates the Fuck Claude browser tool: it reads six locale fingerprints in your browser—system timezone, UI language, installed Chinese fonts, Intl locale, UTC+8 offset, and emoji style—and weights them into a 0–100 risk score. Only the system timezone maps directly onto Claude Code's reported proxy fingerprinting; the rest are broader Chinese-environment signals. Everything runs locally in your browser with no uploads.

What gets scanned

Six weighted signals that mirror the open-source Fuck Claude detector.

  1. System timezone (weight 30): Intl.DateTimeFormat exposes the same OS timezone Claude Code reads. Compared against Asia/Shanghai, Asia/Urumqi and other China zones. This is the strongest signal and the only one with a direct one-to-one mapping to Claude Code's reported mechanism—when Claude Code uses a non-official ANTHROPIC_BASE_URL endpoint, public reverse-engineering reports say it reads OS timezone and encodes results into the system prompt via Unicode steganography.

  2. Browser language (weight 24): navigator.languages reveals your browser's preferred language list. If zh-CN or Simplified Chinese sits at the top, this is one of the strongest non-timezone indicators of a Chinese-localized environment.

  3. Installed Chinese fonts (weight 20): Canvas width-probing detects whether fonts like Microsoft YaHei, PingFang SC, or other Simplified and Traditional Chinese typefaces are installed on your system. Font availability is a notoriously stable fingerprinting vector because it rarely changes between sessions.

  4. Intl locale (weight 10): The locale your browser resolves for date and number formatting. While a weaker signal on its own, it reinforces the picture when combined with language and timezone data.

  5. Timezone offset (weight 8): A quick sanity gate: does getTimezoneOffset() equal UTC+8? This catches cases where the system timezone name might differ from the actual offset.

  6. Emoji rendering style (weight 8): The scanner guesses your OS vendor from the user agent string and maps it to common emoji rendering styles. A weak, loosely correlated signal that acts as a tiebreaker rather than a primary indicator.

How the check works

Understanding the score bands and what Claude Code reportedly reads.

  1. Start scan: Click Start scan to run an animated pass over all six signals. The gauge climbs as contributions add up to a 0–100 risk score.

  2. Low risk (0–30): Your environment shows few or no Chinese locale fingerprints. Claude Code would likely not flag you based on timezone alone.

  3. Medium risk (31–60): One or two signals (e.g., browser language or fonts) suggest a Chinese-localized setup. The timezone may or may not match.

  4. High risk (61–100): Multiple signals align: your timezone, language, fonts, and locale all point toward a China-based environment. Claude Code's check would likely return a positive match.

  5. Focus on timezone: When Claude Code uses a non-official ANTHROPIC_BASE_URL endpoint, public reverse-engineering reports say it reads OS timezone and proxy hostname, encoding results into the system prompt via Unicode steganography. Signals scoring 0.25 or above (relative to their weight) count as individual "hits."

  6. Treat as an estimate: The score is an estimate, not a verdict. Only the system timezone maps directly onto Claude Code's reported check. The other five signals—language, fonts, locale, offset, and emoji style—are probabilistic. A developer running macOS in English with fonts from a previous Chinese-language install might see a medium score even though Claude Code would only flag the timezone.

Is the score accurate?

The score is an estimate, not a verdict. Only the system timezone maps directly onto Claude Code's reported check. The other five signals—language, fonts, locale, offset, and emoji style—are probabilistic. A developer running macOS in English with fonts from a previous Chinese-language install might see a medium score even though Claude Code would only flag the timezone. To lower your score: switch your OS timezone away from China zones like Asia/Shanghai, move zh-CN off the top of your browser language preference list, and avoid Claude Code proxies whose hostnames contain flagged domains or AI-lab keywords.

Sources & References

Authoritative references on browser fingerprinting techniques, timezone-based detection, and the open-source Fuck Claude project that inspired this scanner.
  • “Fuck Claude is an open-source browser tool that reads OS timezone, browser language, installed fonts, and other locale signals to estimate whether a user would be flagged as a "China user" by Claude Code.”
    — Fuck Claude on GitHub

    Fuck Claude — open-source browser fingerprinting tool: This scanner replicates the six-signal detection approach from the open-source Fuck Claude project: timezone, language, fonts, Intl locale, UTC+8 offset, and emoji style, weighted into a 0–100 risk score. github.com/LinXiaoTao/FuckClaude

  • “Canvas-based font probing measures character widths to detect installed fonts without enumerating the system font list. Font availability is a stable fingerprinting vector because it rarely changes between sessions.”
    — MDN Web Docs — Canvas API / Font fingerprinting

    Browser fingerprinting via canvas font detection: The Chinese font check uses canvas width-probing to determine whether fonts like Microsoft YaHei and PingFang SC are installed. This technique is commonly used in browser fingerprinting research. developer.mozilla.org/en-US/docs/Web/API/Canvas_API

  • “The IANA timezone database associates system timezone settings with geographic regions. `Intl.DateTimeFormat` exposes the OS timezone, which can be compared against known regional zones for location inference.”
    — IANA Time Zone Database

    Timezone-based geolocation inference: The strongest signal in this scanner is the system timezone, read via `Intl.DateTimeFormat` and compared against China-standard zones (Asia/Shanghai, Asia/Urumqi). Public reverse-engineering reports indicate Claude Code reads the same OS timezone. iana.org/time-zones

Frequently Asked Questions

Quick answers about this tool—open a question to read more.

Inspired by the open-source Fuck Claude project. For reference only, based on public reverse-engineering reports — not an official statement or advice.