How it works

Paste a link, get back a short one like https://4j.am/K7QX2M and its QR code. The short link is 20 characters when written in capitals, which is exactly what the smallest QR code (21x21 modules, version 1, error correction M) holds. That makes for the simplest possible sticker.

Codes are six characters from an alphabet without look-alikes (no 0 and O, no 1, I and L), so a code read off a sticker types in correctly. Links are case-insensitive.

Rules

• http and https links only, to public hostnames. No links to other shorteners, and nothing that points back here.
• Every new link is checked against Google Safe Browsing, and checked again when it is followed if the last check is a day old. A link that turns bad is disabled.
• Add + to any short link to see where it goes before following it, and to report it. Reported links are disabled pending review.
• Twenty new links an hour per visitor. The same URL always returns the same code.
• Nothing is stored about visitors beyond a hit count per link and a salted hash of the creator's address for the rate limit.