How Are QR Codes Actually Generated?
A QR code generator converts your input data into binary, splits it into data blocks plus error-correction blocks using a technique called Reed-Solomon error correction, and arranges everything into a square grid alongside fixed structural markers. A masking step then adjusts the pattern so it doesn't accidentally confuse a scanner, and the result is the finished QR code.
The first step is encoding. Whatever you type in, a URL, text, WiFi credentials, first gets converted into the most efficient available encoding mode, numeric, alphanumeric, byte, or kanji, and translated into a stream of binary bits. The mode matters because it affects how much room the same content takes up in the final grid, a phone number encoded in numeric mode packs tighter than the same digits encoded as generic byte data.
Before those bits go into the grid, the generator runs them through Reed-Solomon error correction, which adds extra redundant data blocks calculated mathematically from the original content. This is what lets a QR code still scan correctly even if part of it is scratched, covered by a logo, or printed poorly, the redundant blocks let a scanner reconstruct missing pieces, similar to solving a puzzle with a few pieces missing, up to a limit set by the chosen error correction level.
The combined data and error-correction bits then get placed into the grid, working around fixed structural elements that are identical in every QR code: the three finder squares in the corners that let a scanner instantly recognize and orient the pattern, the timing patterns that establish the grid's scale, and the quiet zone margin around the outside. Everything else in the grid is filled with the encoded content and its redundancy data.
Finally, the generator tests several mask patterns, essentially inverting certain modules according to a defined formula, and picks whichever one avoids large blocks of same-color modules or shapes that resemble the finder squares elsewhere in the grid, since those can trip up a scanner's ability to read the code correctly. The chosen mask gets recorded in the format information so any scanner knows how to undo it while decoding.
All of this happens instantly and invisibly the moment you generate a code, you never see the binary or the masking math, you just enter a destination and get a finished pattern back. Understanding the mechanism mostly matters when something goes wrong, like a code that stops scanning after a logo was added without enough error correction headroom built in.