WilliWalli

Work · Personal finance

Debt Free: a budget app in one file

A budget calendar that projects your bank balance months ahead, syncs with a partner in real time, and includes an AI financial advisor — all shipped as a single HTML file.

The constraint

One file, on purpose

The entire app — markup, styles, logic — lives in one 287 KB HTML file with no build step and no dependencies to rot. A recurring-item engine handles every pay-cycle pattern with per-occurrence overrides; bank statements import from four major banks' CSV formats with deduplication and auto-categorization; and a partner joins the shared budget from a single link, synced live through Firebase.

287 KB

the whole app, one HTML file

4 banks

CSV import with auto-categorization

6 months

of cash-flow forecast on the calendar

The AI advisor

RAG with no infrastructure

Semantic memory, client-side

Each question is embedded and compared against the user's own stored past conversations; the best matches are injected as context, and each answer returns a new memory note for the client to keep. Cross-session recall with zero server database.

Grounded and guarded

The advisor sees a live snapshot of the user's actual budget, answers app-usage questions from an injected guide, and runs behind a serverless proxy that keeps API keys off the client and enforces a model allowlist.

How it was built

A design system the AI can follow

The app's visual language is encoded as a custom Claude Code skill — palette, typography, and component specs written down so every AI-assisted edit stays on-brand automatically. It's the same principle as the rest of this portfolio: write the brief first →

Say hello

Curious about any of this?

No pitch — the work is the pitch. If something here sparked an idea, or you'd like a closer look at how a piece of it fits together, I'd genuinely love to talk about it.

Say hello