重定向检查
我们请求该 URL 及其指向的每个 Location，最多 10 跳。每一跳在连接前都会重新解析和检查，并且从不读取响应正文。
此内容尚无中文（中国）版本。在发布译文之前以英语显示。
A link often passes through several addresses before a page appears: http to https, the bare domain to www, a tracking or short link to its target. Each step is an HTTP redirect, a 3xx status code with a Location header.
This tool follows the chain one hop at a time and shows each status code and destination. It marks HTTPS upgrades and downgrades, moves to another host, permanent (301, 308) and temporary (302, 303, 307) redirects, and stops on a loop or after ten hops.
Every hop is resolved and checked again before we connect, so a public URL cannot redirect our server into a private network, and the connection is pinned to the checked address. Only ports 80 and 443 are allowed, and response bodies are never read.
常见问题
301 or 302?
301 and 308 are permanent: search engines move the old address's standing to the new one, and browsers may cache the redirect. 302, 303 and 307 are temporary.
Why does the chain stop at a private address?
A redirect into a private or reserved network is exactly what a server-side request forgery attack uses. We never follow those.
How many redirects are too many?
Each hop costs at least one round trip. One redirect (http to https, or apex to www) is normal; chains of three or more are worth shortening.