A collection of free, practical tools.
Simple utilities that just work. No accounts, no upsells, no clutter — just useful tools, available instantly in your browser.
Tools
Compound interest explorer
Visualize how investments grow over time. Includes monthly contributions, FIRE retirement planning with the 4% rule, multi-currency (37 currencies), inflation and tax adjustments, scenario comparison, year-by-year breakdown, and CSV export.
Open compound.extrautil.com →More tools coming soon
extrautil is a growing collection. Have a tool you'd like to see? The roadmap leans toward calculators, converters, and other lightweight utilities.
Why extrautil
- Free. Every tool, no paywall, no signup.
- Fast. Static pages that load instantly.
- Private. No data collected beyond standard analytics.
- Open. Every input is URL-shareable so you can link any specific scenario.
- Embeddable. Tools support presentation/iframe modes for blogs and dashboards.
- Agent-friendly. Documented URL schemas + an
llms.txton each tool so AI agents can use them programmatically.