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How we build and test our tools

Every tool on FreeToolCabin runs entirely in your browser. This page explains how we build them, how we check that they work and give correct results, and how we keep them up to date.

1. Built to run on your device

Tools are written in plain JavaScript and use well-known open-source libraries (for example pdf-lib, PDF.js, Tesseract.js and FFmpeg compiled to WebAssembly) loaded from public CDNs. Files, text and numbers you enter are processed on your own device and are not uploaded to our servers.

2. Automated testing in a real browser

Before a tool is published, and again before each site update is released, it is opened in a real Chromium browser by an automated test suite that:

  • loads the page and flags any JavaScript error or broken element;
  • runs the tool's main function with sample inputs and files and checks the output (for example, that a converted file opens, a PDF has the expected pages, or a calculation returns the expected value);
  • checks the layout on desktop and on a 390-pixel-wide phone screen, with no horizontal scrolling;
  • checks bad input (empty fields, wrong file types, impossible values) and makes sure the tool shows a clear message instead of failing silently;
  • validates the page's structured data (FAQ, breadcrumbs, application details) and links.

The live site is also crawled regularly: every page in the sitemap is loaded to confirm it responds correctly, and tools that depend on external libraries are exercised end to end.

3. Formulas and figures

Calculators show the formula they use and a worked example with your numbers, so you can check every result yourself. Formulas are checked against worked examples from standard references. Figures that change over time, such as tax brackets, contribution limits and fee rates, are labelled with the year they apply to and can usually be edited on the page. Health, legal and financial tools give general information only and are not a substitute for professional advice.

4. Keeping tools up to date

Each tool page shows when it was last updated. When a library, rate or rule changes, the affected tools are updated and re-tested.

5. Report a problem

If you spot a bug, an incorrect result or an outdated figure, please email [email protected] with the page address and what you expected to see. We review every report.