Nestegg Calculators

A deliberately simple, zero-knowledge personal ledger. Single Cloudflare Worker serving a static frontend (no framework, no bundler) plus three small API routes, with D1 for storage. Login is a Mullvad-style account number; data is encrypted in your browser before it's sent, so the server only ever stores ciphertext.

What it does

• Over time: a stacked bar chart of net worth per year, one colour per asset (or category), with a net-worth line when liabilities exist.
• Allocation: a donut of your most recent year.
• Entry: tap a year to open its editor; each row is one asset (name, currency, value). Add/remove assets, copy the previous year, rename the year.
• Categories: assets can be tagged into a category (e.g. several holdings under "Stocks"). The editor shows each category as a section with a subtotal; charts roll a category up into one segment.
• Long-term assets & loans: a car or house can depreciate/appreciate continuously and carry a loan with a real amortization schedule — extra payments, rate-fixed periods, payment-or-term entry. Its net value is injected into every year you own it.
• Multi-currency: each row carries its own currency; everything is shown in your chosen display currency at ECB rates (/api/fx). Past years use that year's year-end rates.
• Ticker/crypto rows: shares × live price via /api/price (Yahoo proxy). Past years freeze to that year's closing price. Only the public symbol is sent upstream — never an account or user identifier.
• Salary: monthly pay per person (gross or net — your choice), with events (raises, job changes), a dual-axis chart, and paste-from-spreadsheet import.
• Budget: a rough monthly "what's left" — income from your latest salary month, loan payments pulled from your assets, recurring expenses you enter, grouped into categories with a breakdown donut.
• Forecast & retirement: project net worth forward (contributions, growth, scenario band, FIRE goal) and simulate drawdown with a state pension (flat amount or German Rentenpunkte).
• Sync: zero-knowledge. The account number derives an account hash (the only thing the server sees) and an AES-GCM key (never leaves the browser). Multi-device edits merge per record with tombstones, newest wins. No recovery — keep the number safe; Export JSON is the real backup.
• Share links: publish a frozen, read-only snapshot of chosen sections for an advisor. Each share gets its own AES-GCM key, carried only in the URL fragment; the server stores an unlinkable id + ciphertext. Expires in 30 days, revocable any time.
• Bilingual: English and German throughout — the app (language picker in the profile), the landing pages (/ and /de/), and a public Brutto-Netto-Rechner (English version) that runs the exact salary engine entirely in the browser.

Layout

nestegg.money/
├── src/                  # the Worker: /api/fx, /api/price, /api/vault, /api/share,
│                         # /api/calc/*, /mcp, /.well-known/mcp.json + page routing
├── public/
│   ├── index.html        # marketing landing (generated; German at de/, see scripts/)
│   ├── dashboard.html    # the app — loads one <script type="module" src="js/main.js">
│   ├── brutto-netto-rechner.html  # public net-salary calculator (client-side, per-locale)
│   ├── i18n/             # runtime dictionaries (en, de)
│   ├── lib/              # finance-math: pure calculators incl. finance-math/de/
│   │                     #   (generated BMF PAP Lohnsteuer engines + statutory tables)
│   ├── css/              # base, landing, app styles
│   └── js/               # native ES modules (no bundler); layers point ui → io → domain
│       ├── domain/       #   pure logic, no DOM/network: money, dates, schema, ids,
│       │                 #   loan, asset-value, model, forecast, retirement, merge, store
│       ├── io/           #   effects: crypto (encrypt), storage (localStorage/sync/fetch)
│       ├── ui/           #   DOM: dom, chart-kit, charts, networth, assets, salary, gate
│       └── main.js       #   entry point: cross-cutting wiring + boot
├── scripts/              # generators: per-locale pages, BMF PAP → JS, calculator docs
├── tests/                # node --test: domain math, calculators, MCP, i18n page sync
├── schema.sql            # D1: one row per account (hash → encrypted blob)
└── wrangler.toml

The Worker runs first (run_worker_first) so it can route the landing page vs the app by hostname and handle /api/*; everything else falls through to the static assets binding. The frontend is a plain ES-module graph — the browser loads it directly, no build step.

Deploy

Requires a Cloudflare account and npm i -g wrangler (then wrangler login).

1. wrangler d1 create networth-db → copy the database_id into wrangler.toml.
2. wrangler d1 execute networth-db --remote --file=schema.sql
3. wrangler deploy
4. Open the URL, create an account, save the number.

Local dev: wrangler dev (serves the app with live API + local D1).

Cut a release with npm version patch|minor|major — a version hook stamps the new number into the service-worker cache name (public/sw.js) so clients pick up the new build.

Tests (loan/asset/forecast/retirement math, migrate, multi-device merge, crypto): npm test (runs node --test tests/*.mjs — the pure domain modules import directly, no browser needed).

Calculators & MCP

The finance math is also exposed as 99 stateless calculators any client — including AI agents — can call. They are pure functions of their inputs: no user data, no live prices, no FX lookups (you pass the rate in), no auth. This is a remote service, so your inputs are sent to the server — but it stores nothing and logs no request bodies: each call is computed in memory and discarded.

The German set is the exception that carries data: de-net-salary computes exact Netto for tax years 2023–2026 via the official BMF Programmablaufplan (generated engines under public/lib/finance-math/de/, verified against all 1,008 published Prüftabellen values), with de-abgeltungsteuer, de-kindergeld, de-midijob, and de-rentenpunkte sharing the same verified statutory table. Everything else stays country-agnostic.

• JSON API: POST https://nestegg.money/api/calc/<name> (JSON in, JSON out). GET /api/calc lists them. See public/docs/calculators.md.
• MCP server (Streamable HTTP): https://nestegg.money/mcp — the same calculators as MCP tools, with typed outputSchema, read-only annotations, the docs as resources/*, and canned workflows as prompts/* (mortgage-plan, fire-check, brutto-netto).

Install in an MCP client:

claude mcp add --transport http nestegg https://nestegg.money/mcp

Also published to the official MCP registry as io.github.VladimirWrites/nestegg-calculators (auto-republished when server.json changes on main), with the descriptor served at /.well-known/mcp.json and an llms.txt for agent discovery.

Example (an agent keeps responses small by default, then drills in):

> amortization { amount: 475000, rate: 3.75, mode: "payment", payment: 2869.8, startDate: "2024-04-01" }
  → { monthlyPayment, payments, totalInterest, payoffDate, yearly: [ …per-year… ] }   // summary
> amortization { …same…, detail: "monthly", offset: 0, limit: 12 }
  → { schedule: [ …12 rows… ], scheduleTotal: 204, nextOffset: 12 }                    // paginated

Notes

• New accounts start empty with the current year. Tap the year to add asset rows, use "+ Year" for more, or "Reset" to start over.
• In a plain preview with no backend it runs local-only via localStorage with fallback FX rates; sync, live FX and prices activate once deployed.
• The server can't read your figures, but it can see the size of the encrypted blob, sync times, and your IP — stated plainly in the app footer.

Contributing

Issues and pull requests welcome. The domain logic (public/js/domain/) is pure and covered by tests — run npm test before sending a PR, and add tests for new behaviour there. The ui/ and io/ layers are thin and browser-facing; keep DOM work out of domain/. (package.json version and the service-worker cache name must match — a test enforces it; run npm run sync-version if it complains.)

License

Licensed under the Apache License 2.0. © 2026 Vladimir Jovanovic.