Free Online Utility Tools

A QR code is a picture of text, and the text is usually a URL. It carries no logic of its own, which has two consequences worth knowing. The code cannot be changed once printed, so a QR code pointing directly at a long URL is permanent; pointing it at a short redirect you control means the destination can be updated later without reprinting anything.

Scanning failures are almost always physical. The code needs a quiet zone — clear space roughly four modules wide on all sides — and printing it flush against other elements breaks scanning even when the code itself is intact. Contrast must be strong and the right way round, since inverting a code to light-on-dark defeats many scanners. Size follows scanning distance: roughly 1 cm of printed code for every 10 cm the reader will stand away. Longer URLs produce denser codes that need to be printed larger, which is the practical reason to keep the encoded text short.

A favicon is not one image any more. Browsers request a 16x16 for the tab and a 32x32 for higher-density displays and bookmarks, iOS asks for a 180x180 apple-touch-icon when a site is added to the home screen, and Android reads icons from the web manifest at 192x192 and 512x512.

Two details decide whether it looks right. Design for the smallest size first: a detailed logo that reads well at 512 pixels becomes an unidentifiable smudge at 16, so tab icons usually work best as a single letter or a simplified mark rather than the full wordmark. And place the file where it is expected — browsers request /favicon.ico from the site root regardless of what the page markup declares, so the root file should exist even when the HTML points somewhere else.

The unit and time converters in this group solve a narrow problem precisely, and the errors they prevent are category errors rather than arithmetic ones. The recurring ones: a US gallon is 3.785 litres while an imperial gallon is 4.546, a 20 percent gap; a fluid ounce measures volume and never converts to grams without knowing density; and temperature is the one conversion with an offset, so a difference of 10 degrees Celsius is a difference of 18 degrees Fahrenheit, not 50.

For time, everything up to weeks converts exactly and anything involving months or years is an approximation, because months vary between 28 and 31 days. When a duration matters — a billing period, an SLA, an eligibility window — convert to total days or total seconds, which are unambiguous, rather than to a years-months-days breakdown, which two tools can legitimately report differently.