Show HN: Lunar, a coding harness extensible via Lua

A terminal coding harness. You open lunar

and code.

Simple and fast like Pi <3, 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 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.