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Are you a Claude “China user”?

One click scans the locale and browser signals visible on this page, then estimates whether Claude Code may see your environment as China-like.

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What gets scanned

Eight browser-visible fingerprints, weighted to a 0-100 risk score.

  1. System timezoneWeight 26Claude SameIntl.DateTimeFormat exposes the same OS timezone Claude Code reads; compared against Asia/Shanghai, Asia/Urumqi and other China zones.
  2. Browser languageWeight 20navigator.languages - zh-CN / Simplified Chinese at the top of the list scores highest.
  3. Installed Chinese fontsWeight 18Canvas width-probing for Chinese fonts including Microsoft YaHei, PingFang SC, MiSans, HarmonyOS Sans and OPPO Sans.
  4. Intl localeWeight 9The locale your browser resolves for date and number formatting.
  5. Timezone offsetWeight 7Whether getTimezoneOffset() equals UTC+8.
  6. Chinese browser / WebViewWeight 7Looks for browser and in-app WebView markers such as WeChat, QQ Browser, Quark, UC, Baidu, 360 and phone-vendor browsers.
  7. China-brand device hintsWeight 8Weak user-agent hints for HarmonyOS, Huawei, Honor, Xiaomi, OPPO, vivo, realme and related device families.
  8. Emoji rendering styleWeight 5OS vendor guessed from the user agent; a weak, loosely correlated signal.

Claude Code terminal check

A web page cannot read your shell, proxy or DNS settings. Run these commands locally before using Claude Code.

Proxy and endpoint

Look for non-official endpoints and proxy variables.

env | grep -E '^(ANTHROPIC_BASE_URL|HTTPS?_PROXY|ALL_PROXY|NO_PROXY)='

Shell locale and timezone

Compare terminal timezone and locale with the browser result.

date; node -e "console.log(Intl.DateTimeFormat().resolvedOptions())"; locale

DNS resolver

Check whether DNS resolution is routed through an unexpected network.

dig +short api.anthropic.com || nslookup api.anthropic.com

How the check works

When Claude Code is pointed at a proxy endpoint via ANTHROPIC_BASE_URL, public reverse-engineering reports found it reads your operating-system timezone and the proxy hostname, then hides the verdict inside the system prompt with Unicode steganography. The date separator and four look-alike apostrophes in the “Today’s date” line encode whether you look like a China user.

A web page cannot read everything Claude Code can, but the key browser signal is identical: this tool reads the same OS timezone, then adds seven more browser-visible locale fingerprints - UI language, installed Chinese fonts, Intl locale, UTC+8 offset, Chinese browser/WebView markers, device-brand hints and emoji style - into a weighted score. Signals scoring >=0.25 count as hits; bands are Low 0-30, Medium 31-60, High 61-100.

FAQ

Does Claude really check my timezone?

According to public reverse-engineering reports, when Claude Code talks to a non-official endpoint it reads the OS timezone and proxy hostname, and steganographically encodes the result into its system prompt. The timezone this page reads via Intl.DateTimeFormat is the very same OS timezone.

Is this score the exact check Claude runs?

No. Only the system timezone maps one-to-one onto Claude’s reported mechanism. The other seven signals are common Chinese-environment fingerprints that correlate with it, so treat the score as an estimate, not a verdict.

Why can I score high but still use Claude?

The score describes your browser environment. Reported Claude Code behavior is more specific: it matters whether the CLI is pointed at a non-official endpoint and what proxy hostname is visible. Browser risk and account enforcement are not the same thing.

How do I lower my score?

Switch your OS timezone away from China zones such as Asia/Shanghai, move zh-CN off the top of your browser language list, avoid Chinese in-app browsers for this check, and avoid routing Claude Code through proxies whose hostnames contain flagged domains or AI-lab keywords.

What should I check in Claude Code?

Check ANTHROPIC_BASE_URL, HTTPS_PROXY, HTTP_PROXY, ALL_PROXY, NO_PROXY, shell locale variables and DNS resolution in the same terminal where you run Claude Code.

What if my account was restricted?

This site cannot inspect or fix account status. Use Anthropic’s official warning and appeal flow, and keep this tool as a local environment diagnostic only.

Is any data uploaded?

No. Every check runs locally in your browser and none of the detected signals are ever sent anywhere. The site only loads Google Analytics for anonymous page-view stats.

Account restrictions

If Claude shows a safeguard warning or account restriction, use Anthropic’s official support and appeal process. This tool only explains local environment signals.

Open Anthropic appeal guide

Privacy

Every check runs locally in your browser - your scan results never leave your device. The site only loads Google Analytics for anonymous page-view stats; none of the detected signals are ever sent.