# How the `doctor` Command in Agent Reach Checks Channel Availability and Detects Active Backends

> Explore the Agent Reach doctor command. Learn how it checks channel availability and detects active backends by invoking channel check methods and reading the active backend attribute.

- Repository: [Pnant/Agent-Reach](https://github.com/Panniantong/Agent-Reach)
- Tags: how-to-guide
- Published: 2026-06-27

---

**The `doctor` command iterates through all registered channels in [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py), invokes each channel's `check()` method to probe availability, and reads the `active_backend` attribute to identify which backend tool is currently serving the channel.**

The `doctor` command in the **Agent Reach** repository provides a comprehensive health check system that verifies which platforms are ready for use and identifies the specific backend tools powering each channel. This diagnostic tool orchestrates availability checks across all registered channels by leveraging the extensible channel architecture defined in the codebase.

## Core Health Check Implementation in doctor.py

### The check_all Entry Point

The `check_all` function in [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py) serves as the central orchestrator for the health check process. It retrieves all registered channels via `agent_reach.channels.get_all_channels()` and iterates over each channel to collect status information.

### Channel Availability Verification

For every channel, the code invokes the channel's `check(config)` method, which returns a tuple of `(status, message)`. This method performs the actual health probe, whether it's checking for a CLI tool's presence or verifying API connectivity.

The core iteration logic captures the returned status and active backend:

```python
for ch in get_all_channels():
    try:
        status, message = ch.check(config)          # ← channel‑specific health probe

        active = getattr(ch, "active_backend", None) # ← backend actually serving the channel

    except Exception as e:
        status, message, active = "error", f"体检异常：{e}", None
    results[ch.name] = {
        "status": status,
        "name": ch.description,
        "message": message,
        "tier": ch.tier,
        "backends": ch.backends,
        "active_backend": active,
    }

```

## Backend Detection and Active Backend Resolution

### The Base Channel Implementation

In [`agent_reach/channels/base.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/base.py), the abstract `Channel` class defines the default `check` method. This implementation automatically marks the first declared backend as active:

```python
def check(self, config=None) -> Tuple[str, str]:
    """Check if this channel's upstream tool is available."""
    self.active_backend = self.backends[0] if self.backends else "内置"
    return "ok", f"{'、'.join(self.backends) if self.backends else '内置'}"

```

### Platform-Specific Backend Probing

Concrete channel subclasses override this method to perform real verification. These implementations typically:

- Use `ordered_backends(config)` to respect user-provided backend overrides
- Execute lightweight commands via `agent_reach.probe.probe_command` to verify binary functionality
- Set `self.active_backend` to the successfully verified backend, or `None` if no backends are usable

## Report Generation and CLI Output

### Data Aggregation

The `check_all` function captures results in a dictionary containing `status`, `message`, `tier`, `backends`, and the critical `active_backend` field for each channel.

### Human-Readable Formatting

The `format_report` function in [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py) transforms the raw data into a Rich-styled report for terminal display, showing availability status and active backends for each channel.

## Practical Usage Examples

### Running the Doctor Command

Execute the health check from your terminal:

```bash
python -m agent_reach.cli doctor

```

The above command prints a report such as:

```

Agent Reach 状态
========================================
图例：✅ 可用  [! ] 已装但需配置/登录  [X] 未安装

✅ 装好即用：
  ✅ GitHub — 已安装
  ✅ YouTube — 已安装（当前后端：yt-dlp）
...
状态：[green]7/9[/green] 个渠道可用

```

### Programmatic Access

Access diagnostic data programmatically:

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

cfg = Config()
status = check_all(cfg)
print(status["youtube"]["active_backend"])   # e.g. "yt-dlp"

```

## Summary

- The `doctor` command is implemented in [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py) with the `check_all` function orchestrating health checks
- Channel availability is determined by calling `check(config)` on each registered channel from `agent_reach.channels.get_all_channels()`
- Active backend detection relies on the `active_backend` attribute set during the check process
- The base implementation in [`agent_reach/channels/base.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/base.py) defaults to the first backend, while concrete subclasses perform real tool verification
- Results are formatted via `format_report` for CLI display or accessible programmatically as dictionaries

## Frequently Asked Questions

### How does the doctor command handle channels with multiple backend options?

The `check` method in concrete channel implementations uses `ordered_backends(config)` to iterate through available backends in priority order. It probes each backend using `agent_reach.probe.probe_command` and sets `active_backend` to the first working backend, or leaves it as `None` if none respond successfully.

### What happens if a channel check throws an exception?

In [`agent_reach/doctor.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/doctor.py), the `check_all` function wraps each channel check in a try-except block. If an exception occurs, it captures the error, sets the status to "error", and continues processing remaining channels rather than failing the entire diagnostic run.

### Can I customize which backends the doctor command checks?

Yes, the `check` methods accept a `config` parameter that allows user overrides via `ordered_backends(config)`. You can specify preferred backends in your Agent Reach configuration, and the health check will prioritize those backends when determining availability.

### Where does the doctor command get the list of channels to check?

The command retrieves all registered channels from `agent_reach.channels.get_all_channels()`, which is defined in [`agent_reach/channels/__init__.py`](https://github.com/Panniantong/Agent-Reach/blob/main/agent_reach/channels/__init__.py). This function returns all channel classes registered in the system, ensuring the doctor command checks every available platform.