# Show HN: Lunar, a coding harness extensible via Lua

> Source: <https://github.com/gszr/lunar>
> Published: 2026-08-21 11:07:19+00:00

A terminal coding harness. You open `lunar`

and code.

Simple and fast like [Pi <3](https://github.com/earendil-works/pi), but using Lua for extensions.

Lunar gives the model four tools—`read`

, `write`

, `edit`

, and `bash`

—without imposing a workflow.

```
brew install --HEAD gszr/taps/lunar
```

Or with Cargo:

```
cargo install --git https://github.com/gszr/lunar
```

With no `~/.lunar/init.lua`

, set an API key, an OpenAI Chat Completions base URL, and a model:

```
export LUNAR_API_KEY=...
export LUNAR_BASE_URL=https://api.x.ai/v1
export LUNAR_MODEL=grok-4.6
```

Any OpenAI Chat Completions-compatible endpoint should work.

For lasting configuration, create `~/.lunar/init.lua`

. From Lunar, `/config`

opens this file with `$VISUAL`

or `$EDITOR`

, then reloads it when the editor exits. Read the key from the environment:

```
lunar.models {
  grok46 = {
    id = "grok-4.6",
    window = 500000,
  },
}

lunar.providers {
  xai = {
    base_url = "https://api.x.ai/v1",
    key_name = "XAI_API_KEY",
    models = {
      "grok46"
    },
  },
}

lunar.defaults {
  provider = "xai",
  model = "grok46",
}
export XAI_API_KEY=...
```

Or let Lunar store the credential. Use `/login`

in the TUI (xAI subscription via device code, or a masked API key). `/logout`

removes it.

```
lunar.models {
  grok46 = {
    id = "grok-4.6",
    window = 500000,
  },
}

lunar.providers {
  xai = {
    base_url = "https://api.x.ai/v1",
    key_in = "auth",
    auth_provider = "xai",
    models = {
      "grok46"
    },
  },
}

lunar.defaults {
  provider = "xai",
  model = "grok46",
}
lunar
```

Type a prompt and press Enter. Run `/help`

to see the available commands. Use `/config`

to edit and reload `init.lua`

, or `lunar -c`

to continue the latest mission for the current directory.

Lunar includes `AGENTS.md`

, `CONTEXT.md`

, and summaries from `.agents/skills/*/SKILL.md`

in its context.

Lua extensions are planned. For example, you will be able to replace local `bash`

with execution in a [Runta](https://runta.ai) runtime:

```
-- Planned API; not implemented yet.
lunar.tools.bash = function(cmd)
  local runtime = os.getenv("LUNAR_RUNTIME") or "demo"
  return lunar.sh { "runta", "exec", runtime, "--", "sh", "-lc", cmd }
end
```

Lunar is early software for macOS and Linux. It currently supports OpenAI Chat Completions endpoints. Lua extensions and the Responses API are not implemented yet.