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How Reed-Solomon Error Correction Works

Every QR code embeds your data twice over: once as the actual content, and once as mathematically derived redundancy generated by the Reed-Solomon error correction algorithm. This is the same family of error-correcting code used on CDs and satellite links — it lets a scanner reconstruct the original data even when part of the code is missing, smudged, or physically damaged, by solving for the missing pieces the way you can recover a partially erased equation.

The QR standard (ISO/IEC 18004) defines four correction levels, and this tool lets you choose one: L tolerates roughly 7% of the code being damaged before it becomes unreadable, M around 15%, Q around 25%, and H around 30%. The trade-off is capacity: the redundancy has to live somewhere, so a higher correction level packs less of your actual data into the same physical size — an H-level code holds noticeably less text than an L-level code of identical dimensions. Concrete example: a plain URL like a short link survives fine at level L or M, since there is little risk of damage on a screen. A code printed on a box that will be handled, scuffed and exposed to weather is a different story — there level H's extra redundancy is what keeps it scannable after the surface degrades. That is also exactly why H is the standard choice whenever a logo is placed in the center of a QR code: the logo physically covers part of the pattern, and only the highest correction level reliably reconstructs the covered data.

What to Know Before Generating

The codes produced here are static: your text, link, phone number or Wi-Fi credentials are encoded directly into the image pixels, with no redirect service or expiration date sitting behind them. There is no subscription to keep them working and no third party that could later break the link. Generation happens entirely in your browser — nothing you type is ever sent to a server, which matters especially for sensitive data like a Wi-Fi password.

Pick your correction level based on where the code will live: screens and clean printed pages can stay at L or M for maximum data capacity; anything that will be handled, weathered, or carry an embedded logo should use Q or H. Either way, always test-scan the final code with a phone camera before printing it at scale.