China AI Arbitrage

Are you a Claude “China user”?

One-click check of your browser timezone, language, Chinese fonts and locale to estimate whether Claude Code would flag you as a China user.

100% local scanResults never uploaded
0/ 100
Ready to scan
System timezoneWeight 26Claude SameReady to scan
Browser languageWeight 20Ready to scan
Installed Chinese fontsWeight 16Ready to scan
Chinese vendor fontsWeight 10Ready to scan
Chinese browser / WebViewWeight 8Ready to scan
Chinese-brand deviceWeight 6Ready to scan
Intl localeWeight 6Ready to scan
Timezone offsetWeight 4Ready to scan
Emoji rendering styleWeight 4Ready to scan

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 eight more browser-visible fingerprints — UI language, Chinese fonts, Chinese vendor fonts, Chinese browsers, device brand, 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.

Detection engine based on LinXiaoTao/FuckClaude (MIT)

For reference only, based on public reverse-engineering reports. Not an official statement or advice.