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Comment by aerzen | Hacker News Reader

Ok, what about having tools be discoverable from the environment, similar to how $PATH works in POSIX?

There could be an env var $AGENT_TOOLS, a string of paths delimited by `:` and tools would be discovered as some specific format of file. Maybe a JSON that contains tool name, list of parameters and the command to run it.

This is essentially decoupling tools from the agent, allowing more customization and per-project environments. It does require shipping and installing more binaries, one for each tool probably.

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This is one of the approaches im considering for my own, Roder.

The approach mostly being communicating over json rpc which has become the standard for MCP so it makes it more approachable to agent developers.

Obviously its very much NOT mcp, its a low level events based rpc system for registering capabilities and extending low level primitives of the agnet itself not the model

The Hermes agent (Python) follows something similar; it defines a HOME dir and enumerates plugins and memory extensions present there.

https://github.com/nousresearch/hermes-agent

Functionally, it fits more in the openclaw space than pi-agent.

I understand the concept, but I don't get what's the advantage over adding in the prompt instructions to use a specific bash command for a specific task, acting as a "custom tool".

The harness clamps what the agent can do. `bash` allows full code execution; a dedicated `mvn` tool might only allow `mvn compile` but not `mvn spring-boot:run`. You could probably implement this with an `allow` list attached to your `bash` tool, but by doing it this way, you can enhance the outputs or perform mandatory checks too.

For instance, Claude likes to run little Python scripts; reviewing them is tedious. Removing `bash` and adding a `python` tool would allow the harness to pre-review and grep for common harmful patterns, or run the `python` script in a `krunvm` or `muvm` to isolate it, etc. This review/isolation would be handled programatically as it's part of the harness; leaving the agent to choose what to do as a skill means the agent can conveniently forget to enforce its own checks.

Good point. There might be a small advantage if one does not want to give bash access. But general answer to "how do add custom tools like we can in pi" is "you don't". Keep it simple.

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