An interactive demo of QR codes' error correction
Hi HN! This is a hobby project of mine that recently landed me my first interview and helped me get my first internship offers. Draw on a QR code, and the health bars will accurately display how close the QR code is to being unscannable. How few errors does it take to break a QR code? How many errors can a QR code handle? Counters at the bottom track your record minimum and maximum damage. (Can you figure out how to break a QR code with 0.0% damage to the actual data region?) Also, click on the magnifying glass button to toggle between "draw mode" and "inspect mode". I encourage you to use…
In plain words
This interactive tool lets users draw on QR codes to explore how error correction works. Users can damage a QR code in real time while health bars show how close it is to becoming unreadable, with counters tracking minimum and maximum damage thresholds. An inspect mode reveals the underlying structure, and users can verify results by scanning with their phone camera. The decoder runs on WebAssembly, making the full simulation available in a browser. It's designed for anyone curious about QR code resilience and how error-correcting codes function.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
Hi HN! This is a hobby project of mine that recently landed me my first interview and helped me get my first internship offers. Draw on a QR code, and the health bars will accurately display how close the QR code is to being unscannable. How few errors does it take to break a QR code? How many errors can a QR code handle? Counters at the bottom track your record minimum and maximum damage. (Can you figure out how to break a QR code with 0.0% damage to the actual data region?) Also, click on the magnifying glass button to toggle between "draw mode" and "inspect mode". I encourage you to use your phone's camera to scan the code as you draw and undo/redo to verify that the code really does break when the app says it does. I wrote the underlying decoder in C++, and it's compiled to WebAssembly for the website. I hope you find it interesting.
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