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by ptramo 814 days ago
https://zat.is uses uppercase base32 for URL checksums, as alphanumeric QR codes can contain 0–9, A–Z (upper-case only), space, $, %, *, +, -, ., /, :. Overhead is only 10% (5.5 bits / 5 bits). All links fit in a 33⨯33px image, margins included, so little point in improving on that for URLs so short. The tradeoff is that the checksum to URL mapping is stored in a backend and networking is required to learn anything about the real URL.