# Show HN: A tiny shell agent in Rust

> Source: <https://github.com/skorotkiewicz/nano-agent>
> Published: 2026-06-11 21:28:11+00:00

A tiny shell agent in Rust. Talks to any OpenAI-compatible API, runs commands with your approval, and stays out of the way.

```
cargo install --path .
export OPENAI_API_KEY=sk-...

nano-agent "what's in this repo?"
```

That's it. Run `nano-agent`

with no arguments for an interactive REPL.

```
nano-agent "fix the failing test"   # one-shot prompt
nano-agent                          # REPL
nano-agent -c                       # continue last session here
nano-agent -s                       # pick a recent session
```

Every command the agent wants to run is shown first:

``` bash
$ cargo test
Approve? [y] Approve  [a] Approve All  [n] Deny:
```

In the REPL: `:q`

quits, `:reset`

starts over, end a line with `\`

for multiline.

Point it anywhere with an OpenAI-compatible API:

```
export OPENAI_BASE_URL=http://localhost:11434/v1   # e.g. Ollama
export OPENAI_MODEL=gemma4
```

Or keep providers in `~/.config/nano/config.json`

(or `./nano_config.json`

):

```
{
  "provider": "local",
  "custom_providers": {
    "local": {
      "provider_type": "openai",
      "base_url": "http://localhost:11434/v1",
      "api_key": "",
      "model": "gemma4"
    }
  }
}
```

See [example_config.json](/skorotkiewicz/nano-agent/blob/main/example_config.json) for the full format.

**MCP tools**— add servers under`mcp_servers`

in the config; their tools are exposed to the model automatically.**Planning mode**— prefix a message with`/mito`

to talk to a separate local planning agent that prepares a detailed handoff before the main model acts (enable`mito-mode`

in the config).**ACP**— build with`--features acp`

to run nano as an ACP stdio agent (`nano-agent --acp`

) or to delegate subtasks to child agents configured under`acp_agents`

. A child's`working_directory`

is its sandbox boundary; without one, its tools are disabled.

Useful environment variables: `OPENAI_API_KEY`

, `OPENAI_BASE_URL`

, `OPENAI_MODEL`

, `NANO_MAX_STEPS`

, `NANO_SANDBOX=0`

(disable bwrap sandboxing).

```
cargo test
cargo test --features acp
```