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.
- 100% local scan
- Results never uploaded
- Open source
What gets scanned
Nine local fingerprints weighted to a 0–100 score, plus an opt-in network deep scan.
- System timezoneWeight 26Claude SameIntl.DateTimeFormat exposes the same OS timezone Claude Code reads; compared against Asia/Shanghai, Asia/Urumqi and other China zones.
- Browser languageWeight 22navigator.languages — zh-CN / Simplified Chinese at the top of the list scores highest.
- Chinese browser / domestic OSWeight 18User-agent tokens for WeChat, QQ, Quark, 360 and Sogou, plus domestic systems like HarmonyOS and Kylin. UCBrowser is excluded as a false-positive trap.
- Installed Chinese fontsWeight 16Canvas width-probing for Simplified / Traditional Chinese fonts such as Microsoft YaHei and PingFang SC.
- Intl localeWeight 6The locale your browser resolves for date and number formatting.
- Domestic GPUWeight 4WebGL renderer string matching a Chinese GPU (Moore Threads, Zhaoxin, JingJia, Loongson) — rare, but a near-certain mainland tell when present.
- Chinese speech voicesWeight 4Whether the OS ships a Simplified-Chinese (zh-CN) text-to-speech voice; suppressed on macOS, which bundles one worldwide.
- Timezone offsetWeight 2Whether getTimezoneOffset() equals UTC+8.
- Emoji rendering styleWeight 2OS vendor guessed from the user agent; a weak, loosely correlated signal.
Deep scan (network)
Unlike the local scan, this tier sends requests to third parties (Google, Baidu, an IP-geo API, STUN) to see where your traffic actually exits. Runs only when you click.
- Firewall reachabilitynetworkRaces Google / YouTube against Baidu — the first blocked while the second loads means you are behind the Great Firewall.
- Exit IP countrynetworkLooks up the country of your exit IP through a public endpoint — is it CN?
- WebRTC public IPnetworkReads your real public IP via STUN; a mismatch with the exit IP exposes a proxy / VPN.
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 five signals are common Chinese-environment fingerprints 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?
No. Every check runs locally in your browser and none of the detected signals are ever sent anywhere. The site only loads standard Google Analytics for anonymous page-view stats.
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.