RoomPot: our room's cooking money, split by an open model

Sachindu Nethmin — Sun, 04 Oct 2026 08:19:27 +0000

This is a submission for the Hacktoberfest Weekend Challenge: Build for a Friend

Built by me together with my roommates and teammates @bimsara_wickramanayaka_10, @chathuraz and @ashan_lima.

What I Built

Four of us share a room: Chathura, Bimsara, Ashan and me. We cook together, so one of us is always running to the shop for rice, eggs, onions or a new gas cylinder.

Most of the time that person is Chathura. Chathura buys whatever the room needs and pays up front. At the end of the month we're supposed to add up everything, divide the total by four, and pay back whoever spent more. We tried keeping it in an Excel sheet, but in practice receipts get lost, someone forgets to add a purchase, and the collecting just... doesn't happen. Chathura ends up quietly covering money nobody remembers to give back, and asking for it feels awkward.

So I built RoomPot for Chathura and for the rest of us. It's a small group chat for the room. Whoever buys something just says it, the way you'd text a friend:

chicken 1.2k, onions 300, tomatoes 250

RoomPot reads the message with an open-weight AI model (Google's Gemma). It knows who is logged in, so it records that person as the payer. It splits the cost between the four of us and keeps a running tally of who owes whom. Nobody has to remember anything or do maths at the end of the month.

What it does:

Log costs by chatting. "rice 1200, eggs 450" works, and so do "Chathura bought bread 200" (credits Chathura) and "shampoo for me and Ashan 800" (splits between just those two).
Receipt photos. Snap the shop bill and every item is logged. Totals, cash and change lines are ignored.
Average daily spend. The number we actually wanted to know: what the room spends per day and per person, plus today's spend, this month, the last 7 days, and a 30-day chart.

Settle up. It works out the fewest payments that clear everyone's debts, with a Mark paid button. You can also just type "gave Chathura 1500".
Ask it anything about our money. "What's our average daily spend and who still owes me?" is answered from our own data.

Demo

Live app: https://roompot.onrender.com

rice 1200, eggs 450, gas 3800
shampoo for me and <a roommate's name> 800
what's our average daily spend?

You can also invite a second account with the room's invite code to see the splitting and settle-up. (It's on Render's free plan, so if it has been idle, the first load takes about a minute to wake up.)

Code

Sachindu-Nethmin / roompot

Shared room budget for roommates who cook together. Chat what you bought; Gemma (open-weight, via Ollama) splits it and tracks who owes whom.

🍳 RoomPot

A shared room budget for roommates who cook together. Tell the group chat what you bought, like "rice 1200, eggs 450, gas 3800", or send a photo of the bill. An open-weight model (Gemma) reads it. It runs on a server by default so it works in any browser, and anyone can switch on private mode to run it inside their own browser instead. It logs the cost under whoever is logged in, splits it between the room, and keeps a running tally of who owes whom. No more "machan, did I give you money for the gas last week?"

Why it exists

Four of us share a room and cook together. Whoever goes to the shop pays, and at the end of the month we add it all up and divide by four. Except someone always forgets to write a purchase down, and someone else forgets…

View on GitHub

How I Built It

Stack: Next.js (App Router), MongoDB Atlas with Mongoose, and Tailwind CSS, deployed on Render.

Gemma is the core. Every chat message goes to Gemma along with the room's member names and a short set of rules. Gemma returns structured JSON:

{
  "intent": "expense",
  "items": [{ "name": "chicken", "amount": 1200 }, { "name": "onions", "amount": 300 }],
  "paidBy": null,
  "splitWith": [],
  "settleTo": null,
  "settleAmount": null,
  "reply": null
}

The intent can be an expense, a payment back to someone, a question, or just chat. From that, the app records the purchase, records the payment, or answers the question using the room's real numbers.

The model is never trusted blindly. Every response is checked with a zod schema. Amounts must be positive and sensible, and names must match real room members. A bad or missing answer falls back to a simple rule-based parser, so the room never stops working. The money maths (balances, the fewest settle-up payments, daily averages in our timezone) is plain, exact code. The AI only does what it's good at: turning messy human text and photos into clean data.

The same open model runs in three places, and switching between them is one setting:

Where	Model	Used for
Render + Google AI Studio	Gemma 4 (`gemma-4-26b-a4b-it`)	The live app. Works in any browser and reads receipt photos.
My laptop, through Ollama	Gemma 4 E4B	Building and testing, fully offline
Inside the phone's browser	Gemma 2 2B through WebLLM (WebGPU)	Optional private mode: after a one-time download, messages and photos never leave the phone. Receipts are read on-device with Tesseract.js.

Before shipping I ran a set of test messages through Gemma: purchases, "someone else paid", partial splits, paying someone back, questions, and a purchase with no price. All 13 were handled correctly, and a printed receipt was read line by line with the total, cash and change ignored.

Why Does Open Innovation Matter?

Our money is personal. Who bought what and who owes whom is our business. Because Gemma's weights are open, the same model family can run inside a phone's browser, so private mode keeps every message on the device. With a closed API, the only option would be sending everything to someone else's server.
It costs nothing to run. Four roommates splitting cooking costs are not going to pay for an AI subscription. Ollama on a laptop is free, the in-browser model is free, and Gemma on Google AI Studio's free tier is free.
It works offline. On my laptop with Ollama, RoomPot keeps working with no internet at all. That's how I built and tested most of it.
No lock-in. The model is one environment variable. Moving from Gemma 3 to Gemma 4 was a one-line change, and the same code also works with any OpenAI-compatible open-model server.

To be honest about the trade-off: in the hosted version, messages are sent to Google AI Studio to be read by Gemma. Private mode exists for anyone in the room who doesn't want that.

What My Roommates Said

I sent the link to the room. Bimsara tried it first and messaged me:

"Machan, just tested it. It works perfectly, way better than our messy Excel sheet."

(Machan is Sri Lankan slang for "buddy".)

Prize Categories

Best Use of Gemma: Gemma 4 powers the live app and my offline setup, and Gemma 2 2B runs in the browser for private mode.
Best Use of Render: the app is deployed as a Render web service, built straight from the GitHub repo.
Best Use of MongoDB Atlas: Atlas is the data layer for users, rooms, purchases, payments and the chat history behind the open-weight model.

I built RoomPot with help from an AI coding assistant. The idea, the problem, the decisions, and testing it with my roommates are ours.

My Academic Journey at Sabaragamuwa University of Sri Lanka

Sachindu Nethmin — Wed, 28 May 2025 15:36:20 +0000

What I Experienced in My Studies at Sabaragamuwa University

My heart was full of joy, curiosity and some fear when I opened the gate at Sabaragamuwa University of Sri Lanka. I understood from my study in the BSc (Hons) in Computing and Information Systems that I was getting ready for a time in life that would influence both my learning and career goals.

The use of Technology as a Firm Support

The first year built the essential basis for what was to come. Since the beginning, the CIS program showed me the fundamentals of programming, computer systems and problem fixing. When I wrote and tested my first program as a student, I still remember the thrill of seeing it work successfully in the lab. With experience, I have learned about software engineering, database systems and computer networks necessary components needed to be a professional in IT.

What stands out to me most in the program is how it blends learning about science with actual hands-on activities. Every time I go to a lecture, I can become involved in lab sessions that teach me with real-life activities. Through my partnership in these sessions, I have gained better critical thinking and technical abilities.

A Culture of Collaboration and Innovation

At Sabaragamuwa University, education extends well outside the classroom. I have had the opportunity to be part of group projects, coding competition, and student initiated projects. This has provided me with lessons on teamwork, time management, critical thinking and finding creative ways to solve difficult problems.

Open-source contribution and community participation are strongly emphasized here, and I have already participated in several exciting opportunities that make the classroom learning as well as the goals out there very tangible. From contributing to a GitHub project, to brainstorming during hackathons, I’ve found limitless ways to stay motivated and involved.

Mentorship That Matters

The best part of my academic experience has been the mentorship from our lecturers and mentors. They are not just professionals in their jobs but truly invested in our success. Their advice has inspired me to venture beyond the syllabus, reach out in independent study, and even look ahead towards research experiences.

Their never ending support just helping me to be on the right track. I’m interested in machine learning, cybersecurity, and software development, among those areas, I want also to find some internships and side-projects in order to level up my skill-sets.

Looking Ahead

I am in my second year and feeling more confident and determined than ever. The path has not been easy, but each obstacle has served as a steppingstone in becoming more hardened and clear-minded. I think if I continue trying and remain curious and passionate I may do great thinks in technology.

It is not just a place of lectures to me, it is a place where I found myself and who I want to be. Blockquote Sabaragamuwa University of Sri Lanka.

Thanks for reading! If you are a student, a comp-sci enthusiast or just want to say hi, you can reach out and share your academic experience with me too. Let’s motivate and develop each other.

DEV Community: Sachindu Nethmin