22 Client-Side Financial Calculators
& Developer Utilities
JustOnlyOneThing is a free, web-based platform containing 16 financial decision calculators and 6 developer utilities. Every tool executes 100% locally in the user's browser using JavaScript, with zero external network requests, zero backend databases, and zero tracking cookies.
Why Financial Calculators and Developer Tools Are Combined
A Developer's PerspectiveJustOnlyOneThing was created by Saurabh Passolia, a software engineer who actively manages personal investments and uses developer utilities on a daily basis. Instead of visiting ad-heavy websites that sell user data or require email sign-ups, this platform provides fast, deterministic, client-side tools with transparent mathematical formulas.
Both financial decision-making and software engineering rely on deterministic logic and mathematical precision: calculating mortgage amortizations, compounding equity returns, evaluating startup runway, formatting JSON, debugging regular expressions, and verifying cryptographic tokens.
Total Client-Side Privacy
Your financial figures, salary data, debt obligations, cryptographic keys, and raw tokens never leave your machine. There is no backend database, no telemetry, and no tracking scripts.
Sub-Millisecond Speed
Everything is engineered with vanilla ECMAScript and native Web APIs. Sliders update charts in real time at 60 FPS without waiting on server round-trips.
Global Localization
Native presets for India (INR, Lakhs/Crores, Sec 24b/80C tax rules), USA (USD, Millions, 30-year amortizations), UK, Canada, Australia, Germany, UAE, and Singapore.
Popular Decision Engines & Utilities
Explore some of the most frequently used tools on JustOnlyOneThing:
Compare 30-year unrecoverable homeownership costs against renting with an equity investment portfolio.
Forecast mutual fund wealth creation, compounding returns, and annual contribution increments.
Calculate monthly mortgage payments, principal breakdown, and complete repayment schedules.
Format, lint, tree-inspect, query, and compare JSON documents side-by-side with zero latency.
Decode Base64URL claims, inspect expiration timers, and verify HMAC signatures in-browser.
Compute MD5, SHA-256, SHA-512 hashes, HMAC signatures, and AES-256-GCM encryption client-side.
Open, Transparent Architecture
Built on modern web standards with semantic HTML5, Vanilla CSS custom properties, and client-side JavaScript. No heavy frontend frameworks or vendor lock-in.
Contact & Feedback
Have a question about mathematical models, want to report a bug, or have a suggestion for a new financial calculator or developer utility? We welcome community feedback.