How these pages are made and tested

This page says who I am, how a page gets from an idea onto the site, how it is tested, and what happens to the data you enter.

Who makes these pages

I am Simpli, a private individual in Slovakia, and I run this website.

Why this site exists. The school section, in Slovak, is for my children and their classmates — study material to help them learn. The labs and tools are mostly things I am curious about and wanted to try for myself. The games are ones that caught my attention and might entertain others too.

Who tries the pages. I try most of the pages myself, and my children use the school section and play some of the games.

How a page is made

I decide which pages get made. The English tools, games and labs then go through these steps:

Specification. Each page starts with a written description of what it should do. Since 20 October 2026 it also has to say what the page will do better than the first three search results for the same task.
Building. The page is built from that specification. Every page is one HTML file that contains its own code and styles, so the page content does not depend on libraries or fonts from other sites.
Automatic tests in Chrome. A test script opens the page in Chrome and uses it. These tests have been required for new labs since 2 October 2026 and for new tools since 6 October 2026: the page has to work on a desktop screen and on an emulated phone (375 × 740 pixels, with touch), with mouse, touch and keyboard. Since 6 October 2026 the test also types known inputs into new tools and compares the results with values worked out separately, not taken from the page's own code.
Light and dark mode. The existing pages got a dark version between 15 and 17 October 2026. Since then new pages are made and checked in both modes.
A first visit, step by step. Since 8 October 2026 the test also goes through each new interactive page the way a first-time visitor would: only real clicks, taps and key presses, from loading the page to the result, checking after every step that it is clear what to do next. This step was added after the Hearing Test passed all its scripted checks and the first person who used it still got stuck.
Playing the games. Since 14 October 2026 the independent check below plays each new game for several minutes, and a simulated player that reacts with a short delay tests whether a person could actually control it.
An independent AI check. Since 6 October 2026 an AI agent that took no part in building the page tries the finished page with its own test values and reports what does not work.
Fixes. What the tests and the check find is corrected, and that part is tested again.

The phone tests run on an emulated phone in a desktop browser. The school materials are prepared in a different way: see About.

Your data

Nothing you type or record is uploaded.
Pages that use your microphone, or the sound of a browser tab or screen that you share, analyse the sound on your device. Your browser asks for permission first. The list of these pages is in the Privacy Policy.
The exception is the Voice Dictation tool. It uses your browser's speech service, which may send your voice, and with an online voice also the text it reads aloud, to the company that makes the browser (details).
To count visits I use Cloudflare Web Analytics. It works without cookies, and I only see totals such as page views, countries and device types.
The site may show ads from Google AdSense. How ads, cookies and your consent work is explained in the Privacy Policy.

Limits

The pages about health, money and hearing give estimates and explanations. They are not medical or financial advice, and the hearing labs do not replace a hearing test done by a professional.

Found a mistake?

If a page shows a wrong result, does not work on your device or explains something badly, please write to me: the address is on the Contact page. Tell me which page it was and what you saw.

Corrections that have already been made are listed, with dates, on Changes and corrections.