How the test works
When you choose an image, the checker draws it onto an off-screen canvas and hands the raw pixels to jsQR, an open-source decoder that hunts for the finder patterns, samples the module grid, and reconstructs the encoded data. It is the same approach a phone camera approximates in real time, so a clean read here is good evidence the code is recoverable. Because every step happens in this tab, the picture you supply is the whole story — we never see the colors, dimensions, or quiet zone you originally chose, only the finished image you hand us.
If it fails to scan
A failed decode rarely means the code is “broken” — usually one fixable thing is starving the decoder. The frequent culprits are weak luminance contrast (not just a different hue), a quiet-zone margin that got cropped, a logo or sticker eating into the pattern, inverted light-on-dark colors, or simply a soft, angled, or low-resolution photo. We can’t measure those from a single image without the originals, so treat them as a checklist rather than a verdict. The deep dive on why a QR code won’t scan walks through each cause and its fix.
Frequently asked questions
Is my image uploaded anywhere?
No. The image you choose is read straight into this browser tab, drawn to a hidden canvas, and decoded locally. It is never sent to a server and nothing is stored — close the tab and it's gone.
Why did a code that 'looks fine' to me fail?
A decoder is stricter than a human eye. A code can look clean yet fail because the contrast between modules and background is too low for a camera, the quiet-zone margin was trimmed, a logo overlaps a finder pattern, the colors are inverted, or the photo you uploaded is slightly blurry, skewed, or low-resolution. The image you feed in matters as much as the code itself.
Does a pass here guarantee every scanner reads it?
No single tool can promise that. A pass means a real decoder read your code from the exact image you supplied, which is a strong signal. Phone cameras face angle, glare, distance, and motion that a clean upload doesn't, so still test the final printed or on-screen code on a couple of physical devices before you publish it.
What image format and size should I use?
A clear PNG or SVG export of the code works best. If you only have a photo, fill the frame with the code, shoot it straight-on in even light, and keep it in focus — a tight, sharp image decodes far more reliably than a small or angled one.
Related
References
This tool’s QR generation and scannability checks are grounded in the following standards and primary sources.
- ISO/IEC 18004 — QR Code bar code symbology specification — ISO/IEC — the governing QR standard
- Error Correction Feature — DENSO WAVE — the QR inventor on Reed-Solomon levels (L/M/Q/H)
- Point for Setting the Module Size — DENSO WAVE — quiet zone, module size & scanning distance
- Understanding SC 1.4.3: Contrast (Minimum) — W3C WAI — the luminance-contrast ratio used for the scan check
- Color.js — Lea Verou & Chris Lilley (MIT) — contrast + luminance math
- jsQR — Cosmo Wolfe (Apache-2.0) — the in-browser decoder for the scan test
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