QR code scanability checker

Darken the foreground to at least #333333 on white. Below 4:1 the decoder cannot separate modules under real lighting.

The luminance ratio between dark and light modules. Below about 4:1 a camera cannot reliably separate them under indoor lighting, whatever the colours look like on screen. This is the single most common cause of a code that "worked on my monitor" and fails on paper.

Add three more modules of clear white margin on all four sides. The spec requires four; anything less and adjacent artwork bleeds into the finder patterns.

The clear margin around the symbol. The spec requires four modules. Designers routinely crop it to nothing to fit a layout, which stops the decoder locating the finder patterns — the code becomes invisible rather than merely hard to read.

Reduce the logo to 18% of the code area, or switch on excavate mode so modules are cleared rather than covered.

A centred logo destroys modules, and error correction repairs them. EC-M tolerates roughly 15% damage, EC-H about 30% — but that budget is meant for wear, dirt and glare, not for your logo. We report obstruction as a percentage of code area and warn when it eats the margin reserved for the real world.

Modules must be darker than the background. An inverted code — light on dark — is read by some decoders and rejected by many, especially older Android cameras. We also flag colour pairs whose greyscale conversion collapses to near-identical values.

Modules must be darker than the background. An inverted code — light on dark — is read by some decoders and rejected by many, especially older Android cameras. We also flag colour pairs whose greyscale conversion collapses to near-identical values.

Rounded and dot styles shrink each module, effectively reducing size and contrast at the edges. Gradients are checked at both endpoints, because a gradient that starts dark and ends pale fails only on one side of the code — which is exactly the kind of defect a visual review misses.

Rounded and dot styles shrink each module, effectively reducing size and contrast at the edges. Gradients are checked at both endpoints, because a gradient that starts dark and ends pale fails only on one side of the code — which is exactly the kind of defect a visual review misses.

Raise error correction from L to M. At 38% obstruction even EC-H would struggle, so fix the logo first.

A centred logo destroys modules, and error correction repairs them. EC-M tolerates roughly 15% damage, EC-H about 30% — but that budget is meant for wear, dirt and glare, not for your logo. We report obstruction as a percentage of code area and warn when it eats the margin reserved for the real world.

Print at 34mm or larger, or shorten the payload so the code drops to a lower version with bigger modules.

Divide the printed width by the number of modules. Below about 0.4mm per module, consumer cameras fail at arm’s length. This is what turns "version 4" into a concrete minimum size in millimetres, and it is why payload length is a print decision rather than a technical detail.

The three corner squares, the small alignment squares and the dotted rows between them are how a decoder orients and samples the grid. Artistic styling that softens or recolours them causes total failure, not degradation — so these checks are pass/fail rather than scored.

The three corner squares, the small alignment squares and the dotted rows between them are how a decoder orients and samples the grid. Artistic styling that softens or recolours them causes total failure, not degradation — so these checks are pass/fail rather than scored.

The three corner squares, the small alignment squares and the dotted rows between them are how a decoder orients and samples the grid. Artistic styling that softens or recolours them causes total failure, not degradation — so these checks are pass/fail rather than scored.

A 39-character URL forces version 4. A short link would fit version 2 and print 40% smaller.

Divide the printed width by the number of modules. Below about 0.4mm per module, consumer cameras fail at arm’s length. This is what turns "version 4" into a concrete minimum size in millimetres, and it is why payload length is a print decision rather than a technical detail.

Ink spreads on absorbent stock, thickening dark modules and closing the gaps between them. Converting RGB to CMYK also shifts colours, often darkening them. Both are predictable, and both are checked before you commit to a run.

Ink spreads on absorbent stock, thickening dark modules and closing the gaps between them. Converting RGB to CMYK also shifts colours, often darkening them. Both are predictable, and both are checked before you commit to a run.