About usefulweb
Who runs usefulweb, how the free tools are built and checked, our editorial principles and how to report a mistake.
usefulweb is a collection of free, focused web tools: calculators, checkers, planners, converters and technical explorers. Each tool does one job, shows how it got its answer and can be used by a person in the browser or by a program or AI agent through the same interface. This page explains who is behind it, how the tools are made and what you can expect from us.
Who runs usefulweb
usefulweb is an independent project run by Marcel Flaig, a software developer based in Germany. He is the owner, writes and maintains the tools and is responsible for the content. There is no company, investor or agency behind the site. The full legal notice with the postal address is in the imprint.
The site is available at usefulweb.app. The same content is also reachable at usefulweb.app; the usefulweb.site address is the main one.
What you find here
- 239 free tools in areas such as everyday money and household questions, travel, documents and media, developer and security checks, data and AI infrastructure. Examples are a loan amortization schedule, a password generator, a time zone planner or a DNS and TLS checker.
- Premium apps: larger browser programs (for example a pixel-art and animation studio, a photo editor or a cutting-list planner) with their own tutorials. They run in your browser and are currently free to use.
- A blog with longer articles about the questions behind the tools, always based on numbers the tools actually produce.
- An API and an MCP server for every tool, so scripts and AI agents get exactly the same result as the web page.
Tools do not need an account. Most of them work without JavaScript, too: the form is sent to the server and the result comes back as a normal page.
How the tools are built and checked
Every tool is a small, deterministic program: the same inputs always give the same result. There is no AI model producing answers on the result page, so a result does not change because you ask twice or phrase the question differently.
- Documented methodology. Each tool page has a "How it works" section that lists the formulas, rules and assumptions in plain words, and the result page lists the assumptions that were used for your inputs.
- Sources. Where a tool relies on laws, standards, published rates or datasets, the sources are named on the page, with the date they were retrieved.
- Worked examples. Every tool comes with ready-made examples you can open with one click, so you can see what a typical input and result look like before entering your own numbers. Many tools also have a written guide with a step-by-step example.
- Automated tests. About 2,700 automated tests run before every release. They check the calculations against known values, compare the web page, the JSON API and the MCP interface for identical results, validate every result against its published schema and check translations, accessibility basics and security rules.
- Versioning. Each tool has a version number that is included in every result, and the site itself is released in numbered versions. When a calculation changes, the version changes with it.
None of this makes a tool infallible. Rules change, edge cases exist and a dataset can be out of date. That is why results show their assumptions instead of hiding them, and why corrections are welcome.
Editorial principles
- No affiliate links. Tools and articles do not earn commissions on products they mention, and recommendations are not for sale.
- Advertising only with your choice. The site is financed by advertising (Google AdSense). Ads and statistics are loaded only after you have made a choice in the consent dialog, and ads are always visually separate from tool results. Advertisers have no influence on what a tool calculates.
- Clear disclaimers. Tools that touch money, law, health or safety say what they cannot do. Their results are estimates and checklists, not legal, tax, financial or medical advice.
- Honest limits. If a tool only covers some countries, some file types or some cases, the page says so.
- Corrections. If you find a mistake, report it through the feedback form or by email. Confirmed errors are fixed in the tool, the version number goes up and the fix ships with the next release.
How texts and translations are made
The tools, their descriptions, the guides and the translations into 16 further languages are written with the help of AI tools and then checked: by automated tests (for example, every number in a worked example must come from a real run of the tool, and translations must keep every placeholder and number intact) and by the owner. Machine-assisted translations can still contain awkward or wrong wording. If you notice one, please tell us which page and which sentence. The English version is the reference.
Privacy approach
We try to collect as little as possible. Tool inputs are used to compute your result and are not stored unless a tool clearly says so. Several tools that handle secrets, such as password and key generators, run entirely in your browser. Uploaded files are deleted right after processing; files a tool creates for you are kept for about two hours so you can download them. Analytics and advertising cookies are only used after consent, and you can change your choice at any time with "Privacy / cookie settings" in the footer. Details are in the privacy information.
Contact and error reports
The quickest way to reach us is the feedback form, which is linked on every tool page and automatically includes the page you came from. You can also write an email to games@codemagic.net. The contact page explains what to include in a bug report, and the accessibility statement describes how to report barriers.
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