What Lucentool is
Lucentool is a collection of 221 browser tools and calculators, published in English at the root of this domain and in Simplified Chinese under /zh/. The catalogue covers six areas: developer utilities (JSON, YAML, Base64, cron, regex, hashing), academic and school calculators (GPA, rubric marks, study time, fractions), health and fitness (BMI, heart-rate zones, pregnancy dates, running pace), finance (loans, discounts, margin, unit price), kitchen maths (baking conversions, yeast, pan sizes, rice and water ratios) and everyday living calculators (tiles, paint, mulch, curtains, time zones).
Every entry on the home page is a working tool, not a stub page: open it and you can use it immediately, with no account and nothing to install.
Everything runs on your device
Each tool is a pure front-end application written in plain JavaScript. The text, numbers and files you work with are processed locally in your browser. When you drop a PDF, an image or a ZIP file into one of the file tools, the file never leaves your computer — there is no upload step and no server-side copy, because the site has no backend that could receive one.
The practical consequences are simple: opening a tool does not create an account, closing the tab leaves nothing behind on our side, and the tools keep working when your connection is flaky.
How the tools are built and verified
Every tool starts from a written specification — the formula, the unit system and the reference values — and is implemented twice: once as the page you use, and once as an automated check that runs against the same inputs. Results are compared with published references where a standard exists (NIST and ISO conversions, ACOG and AHA guidance for the health calculators, official tax and interest formulas for the finance tools, and the miller's tables used by professional bakers for the kitchen tools). Ranges that cannot be exact — calories per step, bake-time adjustments, fermentation speed — are marked as estimates directly in the interface instead of being presented as facts.
The full method, including what we test and what we refuse to publish, is documented on the methodology page. When a question needs more room than a calculator allows — where a standard is ambiguous, or two references disagree — it is written up as a long-form guide instead.
What we deliberately do not do
No sign-up walls, no file uploads, no selling of visitor data, and no tools that exist only to wrap a search box. The site is free and currently carries no advertising at all; if advertising is ever introduced, the privacy policy will be updated before the first ad is served, and it will explain exactly which third parties are involved and how to opt out.
Who runs it
Lucentool is an independent project maintained by a single developer who writes the tools, the documentation and the checks. There is no content team and no AI-generated filler: a page is published only after the tool behind it works and its numbers have been checked by hand. The catalogue grows in the direction users ask for, and every suggestion is read personally.
Corrections and feedback
Found a wrong number, a unit that is off, or a tool you wish existed? Use the contact page. Reports about incorrect calculations take priority over feature requests, and the page involved is corrected rather than quietly rewritten.