Kästchen is a QR code maker written from the ISO/IEC 18004 standard, without a library. Type any text and its QR code appears; the options choose the error correction level, a minimum version, the mask, the module shape and the colours, and the code can be saved as SVG or PNG. The Bauplan panel replays how the symbol is built: the finder, timing and alignment patterns, then every data and error correction codeword snaking up and down through the grid, the mask that breaks up awkward patterns, and finally the format and version information. Pointing at or tapping a module tells you what it is.

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point at a module, or tap it

Options
Error correction
Shape
Palette
Export
Bauplan

    Bits
    modecountdataterminatorpad bitspad bytes EC/11
    Masks

    Penalty per mask (lower is better): N1 runs · N2 blocks · N3 finder look-alikes · N4 balance. Tap one to force it.

    Blocks