Work / Abacus

Abacus

A self-hosted personal finance app, fully declarative: no bank connection, ever. You say what happened, in the web app or through an AI agent over MCP, and Abacus keeps the books.

Type
Personal product, open source
Role
Design and development
Year
2026
Stack
Next.js, better-auth, PostgreSQL, MCP server, Zod
Code
pikmine-lab/abacus
Data shown
A fictitious demo account
Abacus overview in its dark theme, for a fictitious person: net worth, account balances over the month, and what is waiting for a decision.

The idea

Most finance apps start from a bank connection. Abacus starts from what you declare, and stays honest by asking you to check your real balances from time to time.

  • The core is a service layer. The web app and the MCP server are two clients with no logic of their own.
  • The MCP interface is written for an AI: an agent can record a movement, settle an invoice or answer a question about your money.
  • Nothing about its first user lives in the code. Banks, clients and amounts are data.
Movements list with dates, counterparties, categories and amounts, fictitious data.
Analysis view over 12 months: money in and out by month, then spending as a map of blocks, from the main groups down to each payment, fictitious data.
Investments view with positions and their value over time, fictitious data.

The interface

  • One view answers one question. A screen is named after what it tells you, not after the table it lists.
  • Reading and declaring are two gestures. Entry lives in a side panel, never in half of a reading screen.
  • Nothing is a dead end. Every total leads to its detail, and every detail knows its way back.
Recurring expenses view, fictitious data.
Side panel open for declaring a movement, fictitious data.
Screen for connecting an AI agent to Abacus over MCP.
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