Overview

Moneh is a personal expense tracker built for private use by my spouse and me. It is split into two services: tracker-moneh, a SvelteKit web app optimized for fast expense entry on phone and desktop, and moneh-gateway, a Fastify API gateway that owns all business logic. Supabase PostgreSQL is the operational store, Actual Budget is the financial system of record, and Google Sheets is kept as a reporting layer for monthly reviews.

Challenges/Problems

• Two sources of truth: Every expense has to land in both Supabase and the Actual Budget ledger. A network failure between the two writes must never leave a duplicate or a silently missing transaction.
• Speed of entry: If logging an expense takes longer than a few seconds, it doesn’t get logged. The app had to be faster than writing it down.
• Budgeting by hand: Setting each category’s budget every month was tedious and easy to forget, especially with credit card and paylater bills landing in the following month.
• Security: Database keys and ledger credentials must not be exposed to the browser, and each user must only ever see their own data.

Solutions

• API Gateway: All traffic goes through a Fastify gateway that holds the credentials, authenticates with HTTP-only session cookies, and calls Supabase with the user’s own session so Row Level Security always applies.
• Saga Dual-Write: Expenses are written with a client-generated idempotency key and move through a state machine (PENDING → SYNCED, or ROLLBACK_PENDING → SYNC_FAILED). A reconciliation engine matches pending records against the ledger using correlation IDs embedded in transaction notes.
• Rapid Capture UI: A one-tap sheet with a large amount input, category and payment-method chips, payee-based autofill, and an Undo toast.
• Automated Budget: Next month’s budget is suggested per category from recent spending (with fixed and manual modes and an income cap). A once-a-day run on first app open saves the suggestion on the 28th and auto-assigns it on the 1st, using a compare-and-set claim so concurrent tabs can’t run it twice.
• Spending Insights: Monthly summaries, daily spending trends, category and payment-method breakdowns, a “why is this category high” explanation, and automatic adjustment of next month’s Bills budget for credit card purchases.
• Multi-User, Multi-Budget: One gateway serves several users, each linked to their own Actual Budget file.

Key Impact

• Reliable Ledger Sync: Idempotency plus reconciliation keeps Supabase and Actual Budget consistent without manual cleanup.
• Fast Daily Use: Expenses are logged in seconds from a phone, so tracking actually happens.
• Hands-Off Budgeting: The monthly budget is planned and assigned automatically, while categories the user sets manually are never overwritten.
• Self-Hosted: Both services run as Docker containers on a personal server.