What error correction level actually changes#
A QR code encodes redundant data so a scanner can still read it even if part of the code is damaged, dirty, or covered by a logo — the error correction level controls how much redundancy is built in. Level L tolerates about 7% damage and produces the least dense, easiest-to-scan code for a given amount of data; level H tolerates roughly 30% but packs the same data into a visually denser pattern. For a code that will be printed small, placed on a busy background, or have a logo overlaid on the center, a higher level is worth the extra density. For a simple link shared on a clean digital screen, level M or even L is plenty.
What can go into a QR code besides a URL#
A QR code just encodes text — a URL is the most common use, but Wi-Fi credentials (WIFI:T:WPA;S:NetworkName;P:password;;), a phone number (tel:+1234567890), an email address (mailto:[email protected]), or plain unformatted text all work the same way. The scanning app on the receiving end is what decides how to interpret the encoded string — a URL opens a browser, a tel: link offers to dial.
Why very long text fails to generate#
A QR code has a hard data ceiling — roughly 2,950 characters at the lowest error correction level, less at higher levels, since more of the code's capacity goes to redundancy instead of data. Past that limit generation fails outright rather than silently truncating the content, which is why a very long block of text or an oversized data string needs shortening (a URL shortener, for instance) before it will encode.