How to Add a Custom Backend Override for a Channel in Agent-Reach

You can override the default backend for any Agent-Reach channel by setting the <channel>_backend key in ~/.agent-reach/config.yaml or the <CHANNEL>_BACKEND environment variable, which reorders the candidate list without removing fallback options.

Agent-Reach is a modular platform router that delegates read and search operations to external CLI tools called backends. Each channel (such as YouTube, Twitter, or Reddit) maintains an ordered list of compatible backends. To customize which backend is tried first for a specific channel, you can add a custom backend override for a channel in Agent-Reach through configuration files, environment variables, or the programmatic API.

Understanding Channel Backends in Agent-Reach

In the Agent-Reach architecture, every channel inherits from the base class defined in agent_reach/channels/base.py. Each channel implementation specifies a list attribute called backends that contains the names of compatible CLI tools in order of preference.

When a channel initializes or runs diagnostics, it calls the check() method, which iterates through the candidate backends and selects the first usable tool. This selected backend is stored in the instance attribute self.active_backend and handles all subsequent operations for that channel.

How Backend Override Works

The core logic for adding a custom backend override resides in the ordered_backends() method of agent_reach/channels/base.py (lines 45-59). This method accepts an optional config parameter and returns a reordered list of candidate backends:

# agent_reach/channels/base.py

def ordered_backends(self, config=None) -> List[str]:
    """Candidate backends in probe order, honoring the user override."""
    candidates = list(self.backends)
    override = config.get(f"{self.name}_backend") if config else None
    if override:
        for i, b in enumerate(candidates):
            if b == override or b.startswith(override):
                candidates.insert(0, candidates.pop(i))
                break
    return candidates

When you add a custom backend override, the method searches for a match (exact or prefix) in the candidate list. If found, it moves that backend to the front of the list (index 0) but preserves all other candidates as fallbacks. This ensures that if your specified backend is unavailable, the channel can still fall back to the default options rather than failing entirely.

Methods to Configure a Custom Backend Override

Agent-Reach provides three mechanisms to inject your override: YAML configuration files, environment variables, and direct programmatic access.

Using the YAML Configuration File

The most persistent method is to edit the user configuration file at ~/.agent-reach/config.yaml. Add a key using the format <channel>_backend followed by the desired tool name:

# ~/.agent-reach/config.yaml

youtube_backend: yt-dlp          # Prefer yt-dlp over the built-in extractor

twitter_backend: bird             # Use the 'bird' CLI instead of the default

After saving the file, any new AgentReach instance will load this configuration and apply the override when ordered_backends() is called during channel initialization.

Using Environment Variables

For temporary or session-specific overrides, set an environment variable using the uppercase format <CHANNEL>_BACKEND. According to agent_reach/config.py (lines 70-78), the Config.get() method automatically reads these variables and passes them to the channel configuration:

export TWITTER_BACKEND=bird
python -m agent_reach.cli read https://twitter.com/example/status/12345

This approach is ideal for CI/CD pipelines or one-off commands where you do not want to modify the persistent config file.

Programmatic Configuration

You can also add a custom backend override dynamically within a Python script using the Config class:

from agent_reach.config import Config
from agent_reach.core import AgentReach

cfg = Config()
cfg.set("twitter_backend", "bird")   # Persists the override in the config file

ar = AgentReach(cfg)
result = ar.read("https://twitter.com/example/status/12345")

The Config.set() method writes the value to the configuration store, making it available for subsequent calls to ordered_backends() without manually editing YAML files.

Verifying Your Backend Override

To confirm that your custom backend override is active, inspect the active_backend attribute after running the channel's diagnostic check:

from agent_reach.config import Config
from agent_reach.core import AgentReach

cfg = Config()
ar = AgentReach(cfg)
status, msg = ar.channels["twitter"].check(cfg.data)
print(f"Active backend: {ar.channels['twitter'].active_backend}")  # e.g., bird

This verification pattern is tested in tests/test_channel_contracts.py, which validates that the override logic correctly reorders the backend priority list while maintaining fallback candidates.

Summary

• Agent-Reach channels use an ordered backends list defined in agent_reach/channels/base.py to select external CLI tools.
• The ordered_backends() method (lines 45-59) implements the override logic by moving your specified backend to the front of the candidate list.
• You can add a custom backend override via the ~/.agent-reach/config.yaml file using the <channel>_backend key, or temporarily via the <CHANNEL>_BACKEND environment variable.
• The Config class in agent_reach/config.py (lines 70-78) handles the merging of file-based and environment-based configuration.
• Overrides are reordering operations, not replacements, ensuring fallback backends remain available if the specified tool is unavailable.

Frequently Asked Questions

What happens if I specify a backend that isn't installed?

If the backend you specify in your custom override is not found or is unusable, the channel falls back to the next available backend in the ordered_backends() list. The logic in agent_reach/channels/base.py only reorders the candidates; it does not remove them, so the channel will attempt the default backends if your specified tool fails the check() diagnostic.

Can I override multiple channels at once?

Yes. You can define multiple <channel>_backend entries in the same ~/.agent-reach/config.yaml file, such as youtube_backend, twitter_backend, and reddit_backend simultaneously. Each key is independent and only affects the channel matching that specific name.

Is the environment variable override permanent?

No. Environment variables provide a temporary override for the current session only. Once you close the terminal or unset the variable (e.g., unset TWITTER_BACKEND), Agent-Reach reverts to the priorities defined in the YAML config file or the channel's default backends list.

Does the backend name need to match exactly?

The ordered_backends() method uses either an exact match or a prefix match (b.startswith(override)). This means you can specify a short prefix if it uniquely identifies the backend, though using the full tool name (e.g., "yt-dlp") is recommended for clarity and to avoid ambiguity.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}