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…
An interactive demo of QR codes' error correction launched on April 25, 2025 with 109 votes, #447 of 7,818 launches that month and more than 95% of that year's launches. The site was still online in September 2026, 1 year on.
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
QR is cool is an interactive demonstration of the error correction built into every QR code. Draw on a QR code and see how the decoder works inside.
Every QR code has built-in error correction . This means that they can still be scanned even if they are damaged, like when a corner is covered or torn off, or when they get drawn on. Pick any QR code to learnfrom qris.cool
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…
Does a similar job
all alternatives →
I open sourced the QR designer from my failed startup2023 · github.com · ▲711My designer is somewhat special, if I do say so myself, as it allows you to put arbitrary designs in the middle area of the QR while still being totally scannable.
- PRPhoto Realistic QR-Codes2020 · qrpicture.com · ▲482
Create high-definition, visually stunning QR codes by controlling QR pixel placement to preserve intricate details. Give your QR code a remarkable first impression.
QR Code / Barcode - Scan AppJun 2026 · apps.apple.com · ▲4Analyze every detail of any QR code / Barcode
Free QR Code Generator2025 · qrcode-generator-gamma-brown.vercel.app · ▲18Hi HN, I built a small QR code editor after repeatedly running into the same problem: once a QR code is printed, the destination is frozen. This tool supports both: Static QR codes (generated entirely client-side) Dynamic QR codes (editable destination after creation) Dynamic QR codes come with a minimal dashboard where you can: Update the QR destination without reprinting See basic scan stats (count, device, time, approximate origin) I intentionally kept the feature set small and avoided heavy analytics or tracking. The goal is something simple that works well for menus, flyers, events, and…
More dev tools this month
the category →
open-source IDE for thoughtful software design. Contribute to devdotfast/whiteboard development by creating an account on GitHub.
Dev tools · 28d ago · github.com
Contribute to reladraw/reladraw development by creating an account on GitHub.
Dev tools · 26d ago · github.com
OpenBot▲362Grok Bot alternative: free, local, open-source, multiplayer
Dev tools · 24d ago · openbot.run
Talanoa▲346Hi HN, I’m a fullstack developer, and honestly, I’ve lost count of how many side projects I’ve worked on over the years. But one idea kept coming back to me: a different kind of email client. It first came to me in 2014: “What if we could handle emails more like conversations?” Every year, I’d revisit this concept in my “Build Notes.” Ten years later, no one had built exactly what I had in mind — so I finally decided to do it myself. That’s how Talanoa was born. I wanted something focused on people, not timelines. I was tired of marking messages as unread just to remember to reply later, or…
Dev tools · 21d ago · talanoa.email
CoreSpeed▲332One MCP for everything your agents need: apps, memory, tools
Dev tools · 29d ago · corespeed.io
Source: Show HN post ↗ · launch text quoted in part
Launched alongside, April 2025
the whole month →
Hi everyone, I built PyXL — a hardware processor that executes a custom assembly generated from Python programs, without using a traditional interpreter or virtual machine. It compiles Python -> CPython Bytecode -> Instruction set designed for direct hardware execution. I’m sharing an early benchmark: a GPIO test where PyXL achieves a 480ns round-trip toggle — compared to 14-25 micro seconds on a MicroPython Pyboard - even though PyXL runs at a lower clock (100MHz vs. 168MHz). The design is stack-based, fully pipelined, and preserves Python's dynamic typing without static type restrictions.…
Dev tools · 2025 · runpyxl.com
The Unsure Calculator is an online tool that lets you calculate with numbers you’re not sure about.
Life & fun · 2025 · filiph.github.io
https://the-pocket.github.io/Tutorial-Codebase-Knowledge/
AI · 2025 · github.com
