Sextante

Personal-finance and FIRE calculators built around the Spanish tax system, plus an aggregated portfolio that your own AI assistant can read and write over MCP.

sextante.fpardo.net (Spanish) · English

Project status

Sextante is live at sextante.fpardo.net. The full source code is released under the MIT licence, so anyone can study it and reuse it.

[!WARNING] Not financial advice. Sextante computes and explains; it never recommends. Every result is an estimate: check anything that matters with a professional and with the AEAT.

What it does

🧮 27 calculators	Compound interest, FIRE with a Monte Carlo simulator over real market history, mortgages, deposits, dividends, DCA, inflation, budget… All run in the browser, need no account and keep every input in the URL.
🇪🇸 Spanish tax engine	IRPF by the AEAT dual-scale method with the regional scale of each common-regime community, Social Security, payroll withholding, self-employed, wealth tax, gift tax and capital gains (FIFO).
📈 Aggregated portfolio	Positions and lots across brokers, prices and FX, P&L, reconstructed history, Trade Republic import and progress towards a FIRE goal.
🧾 Tax-return report	Savings-base figures per tax year in euros at the ECB rate, the two-month rule, dividends and interest, double-taxation credit and the box of the Spanish return (modelo 100) for each figure.
🤖 Remote MCP server	47 tools over Streamable HTTP with OAuth 2.1: the portfolio, the tax report, saved scenarios and every calculator, running the same @sextante/core code as the web.
📚 Wiki	Articles and one explainer per calculator, in Markdown, bilingual (es/en).

Screenshots

Architecture

A pnpm workspace with three packages that deploy as one stack:

Path	What
/ (root)	Next.js frontend (App Router) and BFF: rewrites() proxy /api/* and the OAuth routes to the API, so the browser only ever talks to one origin
apps/api	NestJS + Drizzle + PostgreSQL. Single source of truth for data and identity
packages/core	@sextante/core: pure logic shared by both (calculators, projection engine, tax engine, FX, portfolio breakdown and goal)

flowchart LR
  B[Browser] --> W
  M[MCP client] --> W
  subgraph W[Next.js · BFF]
    UI[Calculators · Wiki · Portfolio UI]
  end
  W -- "/api/* · OAuth" --> A[NestJS API]
  A --> DB[(PostgreSQL)]
  UI -. imports .-> C[["@sextante/core"]]
  A -. imports .-> C

The calculators and the wiki work with the frontend alone; the API is needed for sign-in, the portfolio and MCP.

Running it locally

Requirements: Node 24 (see .nvmrc; 22.13 is the minimum), pnpm and Docker (for the API stack and the backend tests).

pnpm install
cp .env.example .env                     # frontend
pnpm dev                                 # http://localhost:3000

# Optional, for sign-in / portfolio / MCP:
cp apps/api/.env.example apps/api/.env
docker compose up -d --build             # postgres + one-shot migrate + api (:3001)

Day-to-day commands (each package is checked on its own; CI runs all of them):

Frontend (root)	Backend
pnpm typecheck · pnpm lint	pnpm --filter @sextante/api typecheck · lint
pnpm test · pnpm test <path>	pnpm --filter @sextante/api test (needs Docker)
pnpm build	pnpm --filter @sextante/api build

Backend details (modules, migrations, tests): apps/api/README.md. Self-hosting with Docker Compose, secrets, encrypted backups and analytics: docs/DEPLOY.md. What was built and what was decided not to build: ROADMAP.md.

License

MIT © 2026 Federico Pardo García.