# Money-saving & comparison

> A network of 13 focused, deterministic tools. Every tool has a human page, a JSON API, an OpenAPI description and an MCP tool that all return the same result (inputs, result, units, assumptions, sources, timestamps).

## Machine interfaces
- Tool catalog (JSON): https://money.usefulweb.app/api/v1/tools
- OpenAPI (all tools): https://money.usefulweb.app/openapi.json
- MCP server (all tools + workflows): https://money.usefulweb.app/mcp
- Pick a tool for a natural-language request: POST https://money.usefulweb.app/api/v1/tools/prompt-to-tool-router/calculate {"request": "..."}

## Tools
- [Bill Detective](https://billdetective.usefulweb.app/): Spot spikes, price changes and calculation errors across your utility bills. API: POST https://money.usefulweb.app/api/v1/tools/bill-detective/calculate
- [Break-even Explorer](https://breakevenexplorer.usefulweb.app/): When does an investment pay for itself? Payback, NPV and IRR for solar, EVs, heat pumps… API: POST https://money.usefulweb.app/api/v1/tools/break-even-explorer/calculate
- [Bulk Buy Brain](https://bulkbuybrain.usefulweb.app/): Is the bulk pack really cheaper once waste, storage and tied-up cash are counted? API: POST https://money.usefulweb.app/api/v1/tools/bulk-buy-brain/calculate
- [Currency Converter](https://currencyconverter.usefulweb.app/): Convert an amount into several currencies at ECB euro reference rates, with rate date and source. API: POST https://money.usefulweb.app/api/v1/tools/currency-converter/calculate
- [Hidden Fee Finder](https://hiddenfeefinder.usefulweb.app/): Paste a quote, contract or invoice and see every fee, tax, penalty and add-on. API: POST https://money.usefulweb.app/api/v1/tools/hidden-fee-finder/calculate
- [Historical FX Chart](https://historicalfxchart.usefulweb.app/): Chart exchange rates over time from ECB data: min, max, average, change, volatility and CSV export. API: POST https://money.usefulweb.app/api/v1/tools/historical-fx-chart/calculate
- [Inflation Time Machine](https://inflationtimemachine.usefulweb.app/): What was money from one year worth in another? CPI-based, 20 countries, World Bank data. API: POST https://money.usefulweb.app/api/v1/tools/inflation-time-machine/calculate
- [Multi-Currency Invoice Calculator](https://multicurrencyinvoicecalculator.usefulweb.app/): Convert invoice lines in different currencies at ECB reference rates, with VAT, rounding and totals. API: POST https://money.usefulweb.app/api/v1/tools/multi-currency-invoice-calculator/calculate
- [Price Per Everything](https://pricepereverything.usefulweb.app/): Compare products by price per gram, use, serving, hour or year of life. API: POST https://money.usefulweb.app/api/v1/tools/price-per-everything/calculate
- [Salary Reality Check](https://salaryrealitycheck.usefulweb.app/): Compare job offers by real net pay per hour, including commute time and living costs. API: POST https://money.usefulweb.app/api/v1/tools/salary-reality-check/calculate
- [Subscription Stack](https://subscriptionstack.usefulweb.app/): Add up every subscription, spot overlaps and see which ones to cancel and what you save. API: POST https://money.usefulweb.app/api/v1/tools/subscription-stack/calculate
- [Travel Exchange Fee Calculator](https://travelexchangefeecalculator.usefulweb.app/): Compare what cards, ATMs, DCC and exchange bureaus really cost abroad vs the ECB reference rate. API: POST https://money.usefulweb.app/api/v1/tools/travel-exchange-fee-calculator/calculate
- [Warranty Value Calculator](https://warrantyvaluecalculator.usefulweb.app/): Is the extended warranty worth it? Expected payout vs. price and break-even failure rate. API: POST https://money.usefulweb.app/api/v1/tools/warranty-value-calculator/calculate

## Workflows