Handmade utilities for modern builders.
FastTools is an open collection of single-purpose micro-utilities engineered to solve daily business and development tasks with zero latency. No accounts, no paywalls, zero server tracking.
Stripe Fee & Net Payout Calculator
Calculate exact domestic, international, and ACH Stripe fees with minor-unit integer arithmetic. Reverse calculate invoice totals to net exact target payouts.
Visual Crontab Expression Generator
Interactive 5-field cron expression builder with natural English descriptions and next 5 run schedules.
JSON to TypeScript & Zod Schema Converter
Convert raw JSON into typed TypeScript interfaces and Zod validation schemas with zero server storage.
Freelance & Agency Rate Calculator
Reverse calculate your minimum billable hourly rate factoring in taxes, overhead costs, and non-billable hours.
Social OpenGraph & Meta Card Previewer
Preview social share cards across Twitter/X, LinkedIn, Facebook, and Discord with one-click Next.js metadata export.
Engineered for Speed, Privacy & Mathematical Rigor
Most web utilities run heavy backend scripts, inject tracking pixels, or store your inputs on remote databases. FastTools processes 100% of calculations in your local browser thread using minor-unit integer arithmetic to eliminate IEEE 754 float rounding errors. Your numbers and financial data never touch remote servers.