# Human‑in‑the‑Loop Agent via Middleware

This repository contains a minimal example of an **LLM agent** that pauses every time it wants to call an external tool and asks the user for confirmation (`approve` or `reject`).  
The pause is implemented with LangChain’s built‑in `HumanInTheLoopMiddleware`, which automatically generates the prompt, captures the user input, and resumes execution via a `Command`.

> **Why use middleware?**  
> Unlike the `interrupt_before=['tools']` approach that requires manual handling of interruptions, the middleware handles everything internally: it creates the confirmation request, processes the response, and resumes the agent with the chosen decision.

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## 📦 Installation

```bash
# Create a virtual environment (optional but recommended)
python -m venv .venv
source .venv/bin/activate   # Windows: .venv\Scripts\activate

# Install required packages
pip install langchain langgraph openai rich
```

> **OpenAI API key**  
> The example uses an OpenAI model. Set your key in the environment:

```bash
export OPENAI_API_KEY="sk-…"
```

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## 📁 Project Structure

| File | Purpose |
|------|---------|
| `solution.py` | Main script that creates the agent, defines a simple tool (`get_weather`), and runs an interactive loop. |

> The repository contains only one Python file for clarity.

---

## 🚀 Running the Example

```bash
python solution.py
```

You will see something like:

```
User: What's the weather in London?
Agent: (pauses) Подтвердите вызов инструмента get_weather
  - approve
  - reject
Your choice: 
```

Type `approve` to let the agent call the tool, or `reject` to skip it.  
After your decision, the agent continues its reasoning and eventually returns a final answer.

---

## 🛠️ Customizing

### Changing the Tool

Replace the `get_weather` function with any other LangChain tool:

```python
@tool
def get_time() -> str:
    """Return current UTC time."""
    return datetime.utcnow().isoformat()
```

Add it to the `tools` list when creating the agent.

### Adjusting Middleware Settings

- **Interrupt on specific decisions**  
  ```python
  interrupt_on={
      "get_weather": {"allowed_decisions": ["approve", "reject"]}  # no edit option
  }
  ```

- **Custom prompt prefix**  
  ```python
  description_prefix="Please confirm the tool call:"
  ```

### Using a Different LLM

Swap `llm` for any LangChain-compatible model (e.g., GPT‑4o, Claude, etc.):

```python
from langchain_openai import ChatOpenAI
llm = ChatOpenAI(model_name="gpt-4o-mini")
```

---

## 📖 Example Interaction

```
User: Tell me the weather in Paris.
Agent: (pauses) Подтвердите вызов инструмента get_weather
  - approve
  - reject
Your choice: approve
Agent: The current temperature in Paris is 18°C with clear skies.
Final answer: It’s sunny and mild in Paris today.
```

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## 📜 License

This project is provided under the MIT license. Feel free to adapt it for your own experiments.

---