Are you a Claude "China user"?
One click scans your browser environment locally and scores how strongly it resembles a China-user profile.
Hit start scan to wake the mascot.
What gets scanned
Six locale fingerprints, weighted to a 0–100 risk score.
Intl.DateTimeFormat exposes the same OS timezone Claude Code reads; compared against Asia/Shanghai, Asia/Urumqi and other China zones.
Whether getTimezoneOffset() equals UTC+8.
navigator.languages — zh-CN / Simplified Chinese at the top of the list scores highest.
The locale your browser resolves for date and number formatting.
Canvas width-probing for Simplified / Traditional Chinese fonts such as Microsoft YaHei and PingFang SC.
OS vendor guessed from the user agent; a weak, loosely correlated signal.
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 five more browser-visible locale fingerprints — UI language, installed Chinese fonts, Intl locale, UTC+8 offset 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.
Privacy
Every check runs locally in your browser — your scan results never leave your device. None of the detected signals are ever sent.
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.
For reference only, based on public reverse-engineering reports. Not an official statement or advice. Original project on GitHub