How our tools are checked
Every tool on TechCrz is a small program, and a program can be wrong. So before the site is built, a test program runs each tool on inputs whose correct answer is fixed by a standard or can be worked out and looked up. A tool that gives a different answer stops the build.
The last test run (2026-11-14) checked 791 known answers across 86 tools. Every tool has at least 5. This number is read from the file that the test program writes each time it runs.
What a known-answer check is
The check feeds a tool an input, and compares the output with an answer that was not produced by the tool. Examples that are checked:
| Question | Known answer |
|---|---|
| 1 mile in kilometers | 1.609344 exactly (NIST SP 811) |
| SHA-256 of the text abc | ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad |
| MD5 of the text abc | 900150983cd24fb0d6963f7d28e17f72 |
| Weekday of 1970-01-01 | Thursday |
| Monthly payment on 200,000 at 6% over 30 years | 1,199.10 |
| Roman numeral for 1994 | MCMXCIV |
Where Node.js has the same function
Hashes, Base64, query strings, regular expressions and dates are also compared with Node.js itself on many generated inputs, for example byte strings of every length from 0 to 300 for the hash functions, and every day from 1900 to 2100 for the weekday and week number tools.
What is not checked
The test program runs the page code without a browser, with a simulated page. It does not test every phone, browser and screen size, and it cannot judge whether a page is pleasant to use. How a page looks and feels on a real device is not covered by the tests.
Tests prove that the tools give the right answer for the inputs tried. They do not prove that no input can go wrong. If you find one, please use the Corrections page.