Are my financial numbers uploaded to a server?

No. CalcTools is 100% client-side. Every calculation — mortgage, loan, compound interest, tax — runs in your browser as plain JavaScript. There is no backend and no /api route. The site's Content-Security-Policy (connect-src 'self') even restricts which hosts the page may contact, so the privacy guarantee is enforced by the browser itself.

Are the calculations accurate?

Yes — each calculator uses the standard, published formula for its problem (the loan PMT formula, compound-interest future value, marginal tax bands, the HKMA stress-test rule, and so on). The verify suite hand-checks reference values against the implemented math before every build. Still, these are decision aids, not financial advice; confirm with a professional for a binding decision.

How is the currency converter's exchange rate sourced?

The converter ships with a build-time snapshot of exchange rates (taken from a public, no-key exchange-rate API at build time) bundled same-origin — it never makes a runtime request to any server in this MVP build. So currency conversion works offline and exposes no browsing data to a third party.

Do the Hong Kong calculators reflect the current year?

They use the published 2024/25 HK rates: Salaries Tax progressive bands (2%/6%/10%/14%/17%) and 15% standard rate with a $132,000 basic allowance; property Stamp Duty on the smoothed ad valorem band scale; MPF at 5% employee + 5% employer capped at the $30,000 monthly relevant-income limit. Always confirm the current figures on gov.hk before relying on a number for a real filing or purchase.

Does it work offline?

Yes. After the first load the app shell is cached, so every calculator works with no internet connection. Install CalcTools as a PWA and it opens and runs offline.

Does this calculator follow the order of operations?

Yes. Expressions are parsed with full operator precedence: parentheses first, then functions and powers, then implicit multiplication, then × ÷, then + −. So 2+3*4 = 14, and -2^2 = -(2^2) = -4 because the unary minus binds looser than the exponent, matching physical calculators and math convention.

What's the difference between DEG and RAD mode?

Trigonometric functions take angles. In DEG mode sin(30) means 30 degrees and equals 0.5; in RAD mode sin(30) means 30 radians and equals about -0.988. Inverse functions (asin, acos, atan) return degrees or radians to match the mode.

Is it safe to type expressions into this calculator?

Yes. The expression is parsed by a hand-written parser and evaluated as a syntax tree — the page never calls JavaScript's eval or Function on your input. The site's Content-Security-Policy does not allow unsafe-eval at all, which the calculator's design proves is never needed.

Does it have memory keys and history?

Yes — MS stores the current value, MR recalls it, M+ adds to it, MC clears it, and Ans recalls the last committed result. Committed results (= or Enter) stay in a session history list that lives only in this browser tab and clears when you leave.

Does the calculator work offline?

Yes. Everything is plain client-side JavaScript bundled with the page — once CalcTools has loaded, the scientific calculator works with no internet connection.

General

Scientific Calculator

A safe scientific calculator — trig, log, powers, roots, constants, and memory with correct order of operations.

Scientific Calculator

Type or tap — full order of operations, no eval, nothing leaves your browser.

Memory: — · Ans: —

Your numbers never leave your device — all math runs in your browser.

How to use this calculator

Type an expression (or tap the keypad) — e.g. 2+3*4, sin(30), 2^10.
Toggle DEG/RAD for trigonometry.
Press = (or Enter) to commit to history; the live preview under the display updates as you type.

Bookmark Scientific Calculator — it works offline once loaded. Figures are decision aids, not financial advice.