About Tulnest

Tulnestis a growing collection of small, fast, free online tools — calculators, converters, text utilities and developer helpers. Every tool is built to do one job exceptionally well, load in under a second, and run entirely in your browser. There's no sign-up, no marketing wall, and no friction between arriving on a page and getting your answer.

Why this site exists

The free online utility space is full of sites that started useful and slowly turned hostile — thirty pop-ups before you reach the calculator, animations that grab focus mid-typing, calculators that demand an email address before showing a result, ads that overlay the form. Most of those sites still have the right tools underneath the mess; they've just stopped optimising for the visitor.

Tulnestis our attempt to do the boring thing well. Pick a calculator, get an answer, leave. If we manage to also explain the math behind the answer in a way you can follow, that's a bonus — and the goal of every tool's explanatory copy and accompanying blog posts.

Editorial principles

A handful of things we won't do, no matter how much they'd move the metrics:

• No sign-up walls or email gates. Every tool is reachable in one click and produces a result without an account.
• No interstitial or pop-up ads. Display ads exist on the site and help keep it free, but they sit alongside the content, not on top of it.
• No data uploaded unless we say so.The vast majority of tools run entirely client-side. The text you paste, the numbers you enter, the JSON you format are never transmitted to our servers. Where a server-side step is genuinely unavoidable (live currency rates, for example), the tool's page says so explicitly.
• No scope creep into a freemium product.Every tool here will stay free of charge. We're not building toward a paid plan, account management, or saved history. If a feature would require user accounts, we won't add it.

How we build the tools

Each tool starts as a list of three or four questions a real person might be asking, phrased plainly. We then check what most existing implementations get right and what they miss — for example, mortgage calculators that show only principal and interest without property tax, or BMI calculators that don't mention the limitations of the metric. The goal is always to ship a calculator that answers more of the question than the alternatives.

Once the math is in place we add the explanatory copy: a short intro that frames when the tool is useful, a worked example, the formula, and a short FAQ. That context turns a calculator into something you can also learn from.

How we keep numbers accurate

Statutory rates and fee schedules shift over time. We treat them with care:

• Tax brackets and pension rates(e.g. Rwanda PAYE, RSSB pension contributions) live in a single configuration file. When official rates change, we update one constant and every dependent tool updates with it. Each tool that relies on these values shows a visible "Last verified" date and a link to the official source.
• Mobile-money fees(e.g. MTN MoMo Rwanda) are taken directly from the operator's published tariff page and re-checked quarterly. The tool page links to the upstream source so you can verify yourself.
• Live currency ratesare pulled hourly from a reputable open API. We display the timestamp on the tool page so you know how fresh the rate is. We don't use these rates for trading decisions — they're mid-market interbank quotes, useful as a benchmark, not as the rate any retail customer will actually receive.
• Math formulas are checked against well-known authoritative sources (e.g. amortization against standard mortgage formulas, BMI against the NIH definitions, compound interest against textbook present-value / future-value formulae) and tested with worked examples that match published references.

What kinds of tools live here

The site is organised into a handful of categories:

• Calculators — everyday calculators: tip, discount, percentage, age, BMI.
• Finance — money tools: compound interest, mortgage, retirement, FIRE, debt payoff, budget, ROI, rent vs buy, savings goal, loan, credit card payoff, inflation, sales tax / VAT.
• Converters — live currency rates across 20 currencies, and unit converters across length, weight, temperature, volume, area and speed.
• Text Tools — word counter, case converter.
• Developer Tools — JSON formatter / validator.
• Rwanda Tools — country-specific calculators most useful for Rwandan users: PAYE income tax, net salary (gross-to-net with RSSB contributions), MTN MoMo fee calculator.

The Blog

Alongside the tools we publish longer-form explanatory writing on the topics the tools touch — money, math, fintech, taxes. Posts are written by hand, not generated. Each one links to the relevant tool so the reader can run their own numbers immediately. The full archive lives at /blog.

Who runs this

Tulnestis built and maintained by an independent developer based in Kigali, Rwanda. The focus on building globally useful tools alongside specifically Rwandan ones (PAYE, MoMo, RSSB) reflects that — those are tools we needed ourselves and couldn't find good versions of anywhere else.

Missing a tool? Found a bug?

If there's a utility you'd like to see here, or if you spotted a number that disagrees with the official source for a statutory calculation, email hello@tulnest.space. Reader requests drive a substantial share of what we build next, and bug reports get same- day responses.

Privacy and ads

The full privacy policy is at /privacy. Briefly: we use Google Analytics with anonymised IPs for traffic insights, and Google AdSense for display advertising. Both can be disabled in your browser. We don't collect personal data, we don't require accounts, and the calculations themselves stay on your device.