# How the Agent Reach Doctor Command Detects and Reports Active Backend Status

> Discover how the Agent Reach doctor command detects and reports active backend status. Learn about per-channel health probes and backend attribute capture for a clear report.

- Repository: [Pnant/Agent-Reach](https://github.com/Panniantong/Agent-Reach)
- Tags: how-to-guide
- Published: 2026-06-14

---

**The `doctor` command executes per-channel health probes via the `check()` method, captures the `active_backend` attribute from each channel instance, and renders a Rich-formatted report showing which backend is currently active for each supported platform.**

Agent Reach is an open-source automation framework that abstracts multiple platform APIs behind a unified channel interface. The `doctor` command serves as the built-in health checker, verifying that upstream tools are installed, configured, and executable. Understanding how it detects and reports the active backend status is essential for debugging connectivity issues and validating your local environment.

## How the Doctor Command Orchestrates Backend Detection

Channel discovery starts in [`agent_reach/channels/__init__.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/__init__.py), which maintains an `ALL_CHANNELS` list containing instantiated channel classes. The `get_all_channels()` function returns this registry, providing the doctor with a complete inventory of platforms to validate.

When [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py) runs, it iterates over this registry and invokes the health-check protocol defined in the abstract base class.

### Channel Registry and Discovery

The [`agent_reach/channels/__init__.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/__init__.py) file automatically registers every available channel implementation. It exposes `get_all_channels()`, which the doctor command calls to obtain the list of channel objects that require health validation.

### Per-Channel Health Probing

Each concrete channel inherits from [`agent_reach/channels/base.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/base.py). The abstract `Channel` class defines an `active_backend` attribute and a `check()` method that subclasses must override.

During the probe, a channel executes a lightweight command—typically via `agent_reach.probe.probe_command`—to verify that a candidate backend binary exists and responds correctly. When successful, the channel assigns the working backend name to `self.active_backend`.

### Aggregating the Active Backend Status

Inside [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py), the orchestration logic captures the results:

```python
status, message = ch.check(config)            # channel does its own probing

active = getattr(ch, "active_backend", None) # whatever the channel set

```

The resulting dictionary stores `status`, `message`, and `active_backend` for each channel. The `format_report()` function then constructs a human-readable summary using Rich styling.

## Reading the Active Backend from Source Code

The detection mechanism relies on the `check()` method setting the `active_backend` instance variable. In [`doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/doctor.py), the code explicitly retrieves this attribute using `getattr` with a fallback to `None` when no backend is detected.

The `format_report()` function uses the `_name_msg` helper to append the active backend information to the status line. When a channel supports multiple backends and one is active, the report displays "（当前后端： <backend> ）" next to the channel name.

## Running the Doctor Command

Execute the health check from your terminal to see active backend detection in action:

```bash
python -m agent_reach.cli doctor

```

Typical output shows the backend name in dim text:

```

[bold cyan]Agent Reach 状态[/bold cyan]
...
✅ 装好即用：
  ✅  YouTube — YouTube 视频和字幕 [dim]（当前后端：yt-dlp）[/dim]
...
状态：[green]9/12[/green] 个渠道可用

```

In this example, the YouTube channel reports `yt-dlp` as the active backend because its `check()` method successfully probed that executable.

## Programmatically Accessing Backend Status

You can invoke the health check programmatically without using the CLI:

```python
from agent_reach.doctor import check_all
from agent_reach.config import Config

cfg = Config()
health = check_all(cfg)

# Access the active backend for a specific channel

print(health["youtube"]["active_backend"])   # Output: "yt-dlp"

```

This returns a dictionary mapping channel names to their health status, including the detected `active_backend`.

## Summary

- **Channel Registry**: [`agent_reach/channels/__init__.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/__init__.py) provides `get_all_channels()` to enumerate all platforms.
- **Health Probing**: Each channel's `check()` method in [`agent_reach/channels/base.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/base.py) sets `active_backend` after verifying the backend executable.
- **Orchestration**: [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py) loops through channels, captures the `active_backend` attribute, and aggregates results.
- **Reporting**: The `format_report()` function renders active backend information using Rich text formatting.

## Frequently Asked Questions

### What happens if no backend is detected for a channel?

If the `check()` method fails to find a working backend, the `active_backend` attribute remains unset. The doctor report displays the channel status as unavailable or degraded, and the formatted output omits the backend name annotation.

### How does a channel determine which backend is active?

Concrete channel implementations in `agent_reach/channels/<platform>.py` override the `check()` method to test candidate backends sequentially. They typically call `agent_reach.probe.probe_command` to verify binary existence and basic functionality, then assign the first successful candidate to `self.active_backend`.

### Can I use the doctor command in CI/CD pipelines?

Yes. Run `python -m agent_reach.cli doctor` as a validation step. The command returns a non-zero exit code if critical channels are unhealthy, and the JSON-compatible output from `check_all()` can be parsed to verify specific backend availability before deployment.

### Where is the active backend information stored after detection?

The `active_backend` string is stored as an instance attribute on the channel object during the `check()` execution. [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py) extracts this value via `getattr(ch, "active_backend", None)` and persists it in the results dictionary passed to the formatting functions.