CalcSI is a free collection of 71 useful online tools in 15 languages — built with a clear privacy-first principle: your data stays in your browser.
CalcSI is a collection of 71 free online tools, built between 2024 and 2026 for everyday life, study and daily work. From the MD5 hash generator to Base64 encoders, JSON and XML formatters, CSS generators, color tools and financial calculators (BMI, Schengen stay calculator, building savings, real-estate transfer tax) all the way to 14 interactive OpenStreetMap-based maps — such as defibrillators, EV charging stations or dog-friendly places. All tools are available without sign-up, without limits and in 15 languages.
Many online tools on the web today are overloaded with ads, pop-ups, cookie banners and tracking scripts to the point where the actual function almost disappears. We set out to do better: lean, fast tools that do exactly what they should — without detours, without data collection and without a login wall. A go-to place for anyone who just wants to calculate, format or convert something.
Privacy is not a marketing word for us, it is architecture. Practically all calculations — hashes, encoders, formatters, color conversions, financial calculators — run entirely client-side in your browser. Your text, your JSON, your password never leaves your device. We do not set tracking pixels or advertising profiling cookies, apart from consent-based Google AdSense ads that fund the site. And there too: no ads without explicit consent.
In concrete terms, this means for you as a user:
To keep all tools permanently free and available without login, we show unobtrusive ads via Google AdSense — only if you have consented to the corresponding cookie category, of course. These ads fund hosting, domain, licenses and the ongoing maintenance of the 15 language versions. There is no premium tier, no paid features and no paywalls: what you see is everything, and it is free for everyone to use.
CalcSI is operated by an independent developer based in Germany. Behind the project is the wish to make the open web a slightly friendlier place: useful tools, multilingual, without dark patterns. You can find the legal entity and contact details in the imprint; for technical questions, bug reports or tool suggestions please use the contact page.
Missing a particular tool? Spotting a bug, a poor translation or a typo somewhere? Got an idea for a new map or calculator? We are happy to hear from you and regularly add suggestions to our roadmap. Drop us a message via the contact page.