How CalcTools works

Your figures are never uploaded

There is no server. Each calculator is a small pure function that runs as JavaScript in your tab. The Content-Security-Policy (connect-src 'self') restricts which hosts the page may contact, so the privacy guarantee is enforced by the browser itself. The currency converter uses a build-time snapshot bundled same-origin — it makes no runtime request to any currency API in this build.

Real, hand-verified math

Each calculator implements the standard published formula for its problem — the amortizing-loan payment formula, compound-interest future value, the marginal tax bands, the HKMA stress-test rule. A verify suite (npm run verify) hand-checks reference values (for example $100,000 at 6% over 30 years = $599.55/month; HK Salaries Tax on $360,000 = $20,760) before every build, so the math is real and reproducible, not a placeholder.

No WASM, no CDN, no tracking

CalcTools is pure JavaScript math plus inline SVG. It needs no WASM, no Canvas, no Web Crypto, and no cross-origin isolation — so the CSP is one of the simplest in the portfolio (script-src 'self' with no 'wasm-unsafe-eval', no COOP/COEP). Every asset is bundled same-origin.

A note on accuracy

These tools are decision aids, not financial advice. The Hong Kong calculators use published 2024/25 rates — always confirm the current figures on gov.hk before relying on a number for a real filing, purchase, or borrowing decision.