> ## Documentation Index
> Fetch the complete documentation index at: https://langchain-zh.cn/llms.txt
> Use this file to discover all available pages before exploring further.

# 概述

> 在每一步控制和自定义智能体执行流程

中间件提供了一种更精细控制智能体内部行为的方式。中间件适用于以下场景：

* 通过日志记录、分析和调试来追踪智能体行为。
* 转换提示、[工具选择](/oss/python/langchain/middleware/built-in#llm-tool-selector)和输出格式。
* 添加[重试机制](/oss/python/langchain/middleware/built-in#tool-retry)、[回退策略](/oss/python/langchain/middleware/built-in#model-fallback)和提前终止逻辑。
* 应用[速率限制](/oss/python/langchain/middleware/built-in#model-call-limit)、防护栏和[PII检测](/oss/python/langchain/middleware/built-in#pii-detection)。

通过将中间件传递给 [`create_agent`](https://reference.langchain.com/python/langchain/agents/factory/create_agent) 来添加：

```python theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
from langchain.agents import create_agent
from langchain.agents.middleware import SummarizationMiddleware, HumanInTheLoopMiddleware

agent = create_agent(
    model="gpt-4.1",
    tools=[...],
    middleware=[
        SummarizationMiddleware(...),
        HumanInTheLoopMiddleware(...)
    ],
)
```

## 智能体循环

核心智能体循环包括调用模型、让其选择要执行的工具，并在其不再调用工具时结束：

<img src="https://mintcdn.com/hhh-8c10bf0c/jRI9Uh24bT9O5tSI/oss/images/core_agent_loop.png?fit=max&auto=format&n=jRI9Uh24bT9O5tSI&q=85&s=92d697bbbf0448295354920392c65af9" alt="核心智能体循环示意图" style={{height: "200px", width: "auto", justifyContent: "center"}} className="rounded-lg block mx-auto" width="300" height="268" data-path="oss/images/core_agent_loop.png" />

中间件在每个步骤前后暴露了钩子函数：

<img src="https://mintcdn.com/hhh-8c10bf0c/nuzu1mnzaCcJfRiZ/oss/images/middleware_final.png?fit=max&auto=format&n=nuzu1mnzaCcJfRiZ&q=85&s=30e8729fd3bce0b5c6f9195910e80620" alt="中间件流程示意图" style={{height: "300px", width: "auto", justifyContent: "center"}} className="rounded-lg mx-auto" width="500" height="560" data-path="oss/images/middleware_final.png" />

## 更多资源

<CardGroup cols={2}>
  <Card title="内置中间件" icon="box" href="/oss/python/langchain/middleware/built-in">
    探索常见用例的内置中间件。
  </Card>

  <Card title="自定义中间件" icon="code" href="/oss/python/langchain/middleware/custom">
    使用钩子和装饰器构建自定义中间件。
  </Card>

  <Card title="中间件 API 参考" icon="book" href="https://reference.langchain.com/python/langchain/middleware/">
    完整的中间件 API 参考。
  </Card>

  <Card title="测试智能体" icon="scale" href="/oss/python/langchain/test/">
    使用 LangSmith 测试您的智能体。
  </Card>
</CardGroup>

***

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