# 关于 User Agent 规则

Surge 的规则系统中有提供依据 User-Agent 进行判别的规则。使用该规则时请注意：

1. 该规则仅对 HTTP/HTTPS 请求有效。如果是一个 raw TCP 请求中提取的 HTTP header，规则无法生效，需配置 `force-http-engine` 参数，详见[《Surge 官方中文指引：理解 Surge 原理 》](https://manual.nssurge.com/book/understanding-surge/cn/#%25E5%25A4%2584%25E7%2590%2586)。
2. 对于 HTTPS 请求，存在发给 HTTP 代理的 CONNECT 请求 User-Agent 和真实的 HTTP 请求 User-Agent ，两者的内容可能相同也可能不同。前者的内容通常是由系统生成，不可被 app 调整。在未开启 MITM 的情况下，匹配时仅对前者生效。开启 MITM 后仅对后者生效。
3. 在 iOS 15 系统后，系统出于隐私保护考虑，不再于 CONNECT 请求中提供 User-Agent，这意味着对于所有 HTTPS 请求，在未开启 MITM 时，User-Agent 均不可见且规则无法生效。


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://kb.nssurge.com/surge-knowledge-base/zh/technotes/user-agent.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.