wtf is cn-check?

China Access Check is a browser tool that tells you whether your current network setup would be flagged as coming from mainland China by sites like ChatGPT, Claude, or LinkedIn. It reproduces the detection tricks those sites commonly use, scores each one, and gives you a combined verdict about which signals your connection is leaking. It runs on Cloudflare Workers as static pages plus a small edge API, and it stores no data about you. The tool checks a long list of signals and weights each one by how reliable it is. These include where your IP address is geographically registered, whether commonly blocked sites like Google or YouTube are reachable, how fast your connection reaches mainland Chinese sites versus international ones, your browser's timezone and language settings, which DNS resolver you are using, whether your device blocks the Taiwan flag emoji the way mainland Chinese devices often do, and whether WebRTC leaks your real IP address. Physical network delay in particular is hard to hide with a VPN, since it reflects your actual distance from a server rather than what your IP claims. Each check produces a confidence score that gets multiplied by its weight and added up, and the tool also cross-checks signals against each other. For example, if your IP looks foreign but your connection to mainland Chinese sites is unusually fast while connections to US sites are unusually slow, that combination raises suspicion that you are using a proxy that only routes some of your traffic. The final score from 0 to 100 sorts results into rough categories, from very likely to be identified as mainland Chinese to basically undetectable. The project is a Cloudflare Worker with a native JavaScript frontend and no external dependencies for its scoring logic. Setup is npm install followed by a local dev server or a Cloudflare deploy command, with a one-time wrangler login the first time you deploy. One detection check, the DNS resolver check, is optional and requires deploying a small companion service on your own VPS, if it is not configured, that check is simply skipped and does not affect the rest of the score.