This is a submission for the Hacktoberfest Open-Source AI Challenge Week 4: Ghost in the Machine

What I Built

I built Command Casper, a tiny hand-drawn ghost that floats on your screen and haunts your PowerShell terminal.

You type a command but don't press Enter. You press Alt+G. Casper looks at what you typed and turns green, yellow or red:

• 🟢 Green: it only reads things.
• 🟡 Yellow: it changes something, but you can usually undo it (installs, copies, a git commit).
• 🔴 Red: it destroys something or is hard to undo (deletes, overwrites, --force, download-and-run).

This is how casperr reacts when you ask it to evaluate a command !

Click the ghost and a speech bubble opens with a plain-English explanation, plus real facts about your actual folder: "this folder has 7 files, all edited today."

The theme gave me a perfect starting point. One of the example ideas on the challenge page was a haunted terminal that "possesses your shell." I wanted a friendly haunting, though. Casper isn't there to scare you. He's the ghost that says "hold up, human bean, think this through" right before you wipe a folder.

I'm fairly new to all of this, so I kept two rules:

1. It never blocks Enter and never runs your command. It only looks.
2. The AI never decides the colour. More on that below, because it's the most important design choice in the project.

Fun detail: the ghost is original pixel art i took from a template and enhanced myself (the rosy cheeks , the pink bow and ofcourse the signs !)

Demo

Below is the video where you will catch casperr shaking cause of a delete command !

Summon him and release him like this:

. D:\ghost\ghost.ps1
casperr summon     # "Casperr has been summoned!"
casperr release    # "Casperr has returned to the ghost realm!"

When summoned, he drops in from above and settles. When released, he does the same thing in reverse and fades away. Green bobs slowly, yellow a bit quicker, and red is frantic, because red should feel a little panicky.

Code

How I Built It

The model: Gemma 4 26B (gemma-4-26b-a4b-it), an open-weight model, served through Google AI Studio's free tier. No credit card, no cost.

The most important decision: rules pick the colour, the AI only explains.

My first instinct was "let the model judge the command." But a model that can be talked into a different answer is a bad safety guard. So the colour comes from a plain, editable rules.json and a small rule engine: aliases, && chains (the worst command in the chain wins), quotes, > vs >>, and -WhatIf making a command green. Anything unknown defaults to yellow. It's deterministic: same input, same colour, every time.

I tested the engine on 114 commands (37 green, 33 yellow, 44 red) and all pass. The tests also run automatically on every push with GitHub Actions.

The AI arrives afterwards. The bubble opens instantly with template text, then Gemma's explanation fades in a moment later from a background thread. The prompt tells it the verdict is final:

"The verdict is RED and it is final. Never contradict it, never change it. Use ONLY the facts given below."

It only receives the command, the verdict with its reasons, and counts or sizes ("7 files, 18.6 KB"). Never file contents.

If there's no key, no internet, or the API errors out, the bubble just shows the template text. The tool never breaks.

Other bits:
Windows PowerShell 5.1 with one PSReadLine key binding, a small tkinter window, and a plain UDP message to 127.0.0.1 between the two.
The hook lives in the current terminal session only, with no $PROFILE edits and nothing installed system-wide.
The AI part is pure Python standard library, so there's nothing to pip install. Everything lives in one folder.

What the model says

Same prompt, the rules choose the colour, Gemma 4 26B writes the explanation:

Why Does Open Innovation Matter?

• Swapping models is one line. The model name lives in a .env setting. Comparing two Gemma sizes took one flag. The code also speaks the common Open ai style request format, so pointing it at another provider or a local server should be a config change.
• It cost nothing. The whole project runs on a free tier.
• No lock-in for the important part. The thing that keeps you safe is a JSON file you can read, edit and argue with. The model is a replaceable explainer. If a provider changes its rules, Casper falls back to templates instead of dying.

The Spirit of It ( Thoughtfully following the Theme )

Casper is meant to be a gentle kind of spooky. I drew it pixel by pixel, gave it rosy cheeks and a bow and wrote for it lines like "Spooky. Are you sure about this?" and "Watch out, mortal!" The goal was a ghost that makes the scary moment of pressing Enter feel a bit less lonely, and maybe makes you pause for one second before the red command.

The lines live in a plain personality.json, so you can rename it and swap "mortal" for anything you like.

Built by
Misbah · Dev: @misbah_bagwan

Prize Categories

• Best Use of Gemma: Gemma 4 26B writes every explanation, through Google AI Studio.
• Best Use of GitHub Copilot: I used GitHub Copilot in VS Code while building (the repo includes my Copilot instructions file), and the rule tests run automatically on every push with GitHub Actions.

Built with help from AI assistants (Claude and GitHub Copilot). The design decisions, the art, the rules and the testing are mine.

Music credits: nastelbom-halloween-halloween-music-621496 by Nastelbom, from Pixabay

Ghost Template credits :PixilArt