# Everyday calculators

> A network of 7 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://calculators.usefulweb.site/api/v1/tools
- OpenAPI (all tools): https://calculators.usefulweb.site/openapi.json
- MCP server (all tools + workflows): https://calculators.usefulweb.site/mcp
- Pick a tool for a natural-language request: POST https://calculators.usefulweb.site/api/v1/tools/prompt-to-tool-router/calculate {"request": "..."}

## Tools
- [Loan Amortization Calculator](https://loanamortizationcalculator.usefulweb.site/): Annuity, linear or interest-only loans: schedule, extra payments, fixed-rate balance, APR. API: POST https://calculators.usefulweb.site/api/v1/tools/loan-amortization-calculator/calculate
- [One-Rep-Max & Plate Loader](https://onerepmaxcalculator.usefulweb.site/): 1RM from any set (7 formulas + average), % and RPE tables, and which plates to load. API: POST https://calculators.usefulweb.site/api/v1/tools/one-rep-max-calculator/calculate
- [Percentage & Ratio Calculator](https://percentageratiocalculator.usefulweb.site/): X% of Y, % change, reverse %, percentage points, ratios and aspect ratios, with formulas. API: POST https://calculators.usefulweb.site/api/v1/tools/percentage-ratio-calculator/calculate
- [Random Generator](https://randomgenerator.usefulweb.site/): Random numbers, dice, coins, list picks, shuffles, fair teams, dates, strings and UUIDs. API: POST https://calculators.usefulweb.site/api/v1/tools/random-generator/calculate
- [Running Pace & Splits](https://runningpacecalculator.usefulweb.site/): Pace, time or distance in km or miles, splits, race predictions, treadmill speed, laps. API: POST https://calculators.usefulweb.site/api/v1/tools/running-pace-calculator/calculate
- [Sports Travel-Fatigue Estimator](https://sportstravelfatigueestimator.usefulweb.site/): Travel distance, time-zone jumps, rest and back-to-backs per game as a fatigue score. API: POST https://calculators.usefulweb.site/api/v1/tools/sports-travel-fatigue-estimator/calculate
- [Tip & Bill Split Calculator](https://tipbillsplitcalculator.usefulweb.site/): Tip, tax and who pays what: split a bill equally, by shares or by items, rounded up. API: POST https://calculators.usefulweb.site/api/v1/tools/tip-bill-split-calculator/calculate

## Workflows