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Are you a Claude “China user”?

One click scans the locale signals in your browser and tells you whether Claude Code would flag — and ban — you as a China user.

0/ 100
Ready to scan

A browser can’t read your real DNS or proxy. Copy this prompt into your own coding agent (Claude Code, Cursor…) and it runs the real local checks.

What gets scanned

Local fingerprints plus live network probes — including a proxy-transit check — weighted into one 0–100 score.

The network rows below reach out to third parties (Google / Baidu reachability, an IP-geo API, a STUN server) to see where your traffic actually exits — your score itself is never uploaded.

  1. System timezoneWeight 19Claude SameIntl.DateTimeFormat exposes the same OS timezone Claude Code reads; compared against Asia/Shanghai, Asia/Urumqi and other China zones.
  2. Browser languageWeight 15navigator.languages — zh-CN / Simplified Chinese at the top of the list scores highest.
  3. Chinese browser / domestic OSWeight 13User-agent tokens for WeChat, QQ, Quark, 360 and Sogou, plus domestic systems like HarmonyOS and Kylin. UCBrowser is excluded as a false-positive trap.
  4. Installed Chinese fontsWeight 11Canvas width-probing for Simplified / Traditional Chinese fonts such as Microsoft YaHei and PingFang SC.
  5. Intl localeWeight 4The locale your browser resolves for date and number formatting.
  6. Domestic GPUWeight 3WebGL renderer string matching a Chinese GPU (Moore Threads, Zhaoxin, JingJia, Loongson) — rare, but a near-certain mainland tell when present.
  7. Chinese speech voicesWeight 3Whether the OS ships a Simplified-Chinese (zh-CN) text-to-speech voice; suppressed on macOS, which bundles one worldwide.
  8. Timezone offsetWeight 2Whether getTimezoneOffset() equals UTC+8.
  9. Emoji rendering styleWeight 2OS vendor guessed from the user agent; a weak, loosely correlated signal.
  10. Firewall reachabilityWeight 7networkRaces Google / YouTube against Baidu — the first blocked while the second loads means you are behind the Great Firewall.
  11. Exit IP countryWeight 6networkLooks up the country of your exit IP through a public endpoint — is it CN?
  12. DNS routingWeight 5networkResolves transnational domains (Apple, Microsoft…) over DoH to see whether your DNS points them at Chinese CDNs or overseas.
  13. WebRTC public IPWeight 3networkReads your real public IP via STUN; a mismatch with the exit IP exposes a proxy / VPN.
  14. Proxy transit (中转)Weight 12The cross-check: a Chinese local environment whose traffic exits abroad — the mainland-dev-behind-a-proxy signature. Scores when caught.

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 signal is identical: this tool reads the same OS timezone, then adds more browser-visible fingerprints — UI language, Chinese-browser / domestic-OS tokens, installed Chinese fonts, a domestic-GPU check, Intl locale and Chinese speech voices — into a weighted 0–100 score (Low 0–30, Medium 31–60, High 61–100; a signal scoring ≥0.25 is a hit). Because a mainland user on an overseas proxy — the Claude Code case — can spoof all of those, an opt-in “deep scan” then probes the network (firewall reachability, exit-IP country, WebRTC) and flags the tell-tale mismatch: a Chinese local environment whose traffic exits abroad.

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 signals are common Chinese-environment fingerprints and network checks that correlate with it, so treat the score as an estimate, not a verdict.

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, and avoid routing Claude Code through proxies whose hostnames contain flagged domains or AI-lab keywords.

Is any data uploaded?

Your score is not. The local fingerprints are computed entirely in your browser. The network probes do contact third parties (Google / Baidu, an IP-geo API, a STUN server) to check where your traffic exits — that is inherent to measuring your network — but the computed score and signals are never uploaded. The site also loads Google Analytics for anonymous page-view stats.

Privacy

The local fingerprints are computed entirely in your browser. The network probes do reach out to third parties (Google / Baidu reachability, an IP-geo lookup, a STUN server) to see where your traffic exits, but your computed score and signals are never uploaded. The site also loads Google Analytics for anonymous page-view stats.