CircleSplit AI

Inspiration

Group activities should be about spending time together, not chasing payments. Organizers of sports sessions, clubs, and community events need clear shared budgets, fair cost allocation, explicit contributor approval, and trustworthy records.

What CircleSplit AI does

CircleSplit AI combines natural-language event budgeting with PayPal sandbox contributions. Organizers can create an event, add costs and participants, compare exact-cent equal and attendance-weighted splits, review Gemini-generated expense suggestions, approve individual shares, and collect contributions through a PayPal Orders v2 sandbox checkout. The transaction ledger distinguishes simulated contributions, created orders, and verified captured payments.

How we built it

Google Gemini AI (configured as gemini-3.5-flash-lite): calls the Google Generative Language API to extract structured expenses, suggested allocation strategy, and rationale from an organizer's natural-language note. Responses are validated and editable; AI never makes or approves payments. PayPal sandbox REST APIs: server-side OAuth, Orders v2 order creation, buyer approval, capture, exact amount/currency verification, order-status lookup, idempotency, and verified webhook event handling. Payments are strictly sandbox only. Python / FastAPI / SQLite: trusted organizer API, contribution and payment ledger, deterministic integer-cent largest-remainder allocation, and human approval requirements. JavaScript / HTML / CSS: responsive organizer workspace and an independently safe no-login public demonstration. The public demo uses fictional data stored only in the visitor's browser and never calls Gemini or PayPal. Render: hosted web deployment connected to GitHub main; GitHub Actions + pytest: automated backend tests. MIT license: open-source repository.

Working demo

Public guest experience (no login): https://circlesplit-ai-demo.onrender.com/ Public judge walkthrough: https://circlesplit-ai-demo.onrender.com/judge Protected integration workspace: https://circlesplit-ai-demo.onrender.com/workspace (separate expiring judge login, credentials supplied with testing instructions) Public source, setup, and tests: https://github.com/betterlifestyle04-commits/circlesplit-ai

Verified integration results (November 2–3, 2026)

We ran a real Gemini request through the hosted organizer workspace: the model extracted court $180, equipment $25, and refreshments $30, returned a rationale and editable proposals, and the API reported HTTP 200. We also completed a PayPal SANDBOX $11.00 USD purchase for the fictional "Friday Community Volleyball" event. The server received a successful Orders v2 create response, a buyer return from PayPal, HTTP 200 on the capture endpoint, and HTTP 200 on the webhook endpoint. The CircleSplit ledger displayed VERIFIED CAPTURE for the corresponding participant. These are test funds, not real revenue.

Known limitations and safety boundaries

This remains a hackathon MVP rather than a production payments service. The public guest site is simulation-only; judges need separately supplied test credentials to exercise the real Gemini and PayPal sandbox integration in the organizer workspace. Render Free uses ephemeral SQLite storage; saved demo records can reset across deployments or restarts. Separate owner and time-limited judge Basic-auth logins are for controlled sandbox testing only, not individual participant identity verification. No production money movement, escrow, or merchant payout splitting is claimed.

Remaining before final hackathon submission

Record and upload a public YouTube demo video under 3 minutes that shows the live Gemini AI response and PayPal sandbox capture; provide judge testing instructions/credentials through an appropriately restricted judging channel; verify the GitHub repo license appears properly; and submit all required Devpost fields by November 12, 2026.

Built With

• fastapi
• gemini-ai
• github-actions
• javascript
• paypal-rest-api
• python
• sqlite