QR Codes Explained: How They Work and How to Use Them Safely
QR codes are everywhere — on restaurant menus, packaging, posters, business cards, event tickets and payment terminals. They are a fast way to share a link or piece of information without anyone needing to type it. This guide explains what they are, how they work, what kinds of information they can carry, and how to create and use them safely.
What is a QR code?
QR stands for Quick Response. A QR code is a two-dimensional barcode — a square pattern of black and white modules — that stores information. Unlike a traditional one-dimensional barcode that stores data in a single row of stripes, a QR code stores data in both horizontal and vertical directions, allowing it to hold far more information in a compact space.
The three square finder patterns in the corners allow a scanner to detect the code's position and orientation regardless of the angle it is held. This means a QR code can be scanned upside down, at an angle, or from across a room (at large size) without error.
How a QR code stores data
The data is encoded in the pattern of modules using a specific binary encoding scheme. Error correction data is also embedded — a QR code at the highest error correction level can still be read correctly even if up to 30% of it is obscured, damaged or covered by a logo. This is why QR codes with company logos or decorative elements in the centre still scan correctly.
The capacity of a QR code depends on its version (size), the type of data being encoded and the error correction level. A simple URL of around 30 characters produces a relatively simple, low-density code. A long URL or a block of plain text produces a denser, more complex pattern that may be harder to scan from a distance or when printed small.
What types of content can a QR code contain?
A QR code can encode any text string. What happens when you scan it depends on how the content is formatted and what your phone does with it. Common payload types include URLs (which open a web page), plain text (which displays on screen), email addresses (which open an email draft), phone numbers (which prompt a call), SMS messages (which open a text draft), Wi-Fi credentials (which prompt to join a network) and vCard contact details (which prompt to add a contact).
The QR code itself does not do anything — it just stores text. It is the phone's scanner app and operating system that interpret the content and decide what to do with it.
Creating a QR code
To create a QR code, you enter the content you want to encode, choose the payload type and generate the image. The Quick QR tool handles this in a few clicks. Key decisions when creating a code:
- Content accuracy: A typo in a URL produces a code that scans but goes nowhere. Double-check the content before generating.
- Size: Generate at the largest practical size for your intended use. A code generated at 200×200 pixels looks fine on screen but may be blurry when printed at A5 or larger. Generate at 1000×1000 pixels or higher for print.
- Error correction level: Higher error correction (level H) means the code can survive more damage but produces a denser pattern. For most uses, medium (level M) is a good balance.
- Test before publishing: Always scan the generated code with at least two different phones before printing or sharing it.
Tips for printing QR codes
A code that scans perfectly on a monitor may fail when printed if not prepared correctly. Follow these guidelines for reliable printed codes:
- Leave a clear white margin (called the quiet zone) of at least four module widths around all sides. Printed elements that intrude into this margin will cause scanning failures.
- Minimum print size for reliable scanning is approximately 2 cm × 2 cm, but larger is better — especially for codes with dense content or high error correction.
- High contrast between the modules and background is essential. Black on white is optimal. Dark on light works well. Light on dark may fail on some scanners.
- Print a test page and scan it before committing to a large print run.
- QR codes on glossy surfaces can cause reflections that interfere with scanning in bright light.
Staying safe when scanning QR codes
The QR code pattern itself is harmless — it is just encoded text. The risk comes from what it points to. A QR code can contain a URL pointing to a phishing site, a malicious download or a fraudulent payment page just as easily as a legitimate one. Some points to bear in mind:
- Most phone camera apps show a preview of the URL before opening it. Check this preview — does the domain look legitimate? Is it HTTPS? Does it match what you expected?
- Be cautious of QR codes in public places that have been placed over or next to official codes — this is a known scam technique, particularly on parking meters and restaurant tables.
- If scanning a code asks for personal information or payment details unexpectedly, stop and verify the source through another channel before proceeding.
- QR codes in emails from unknown senders should be treated with the same caution as links in those emails.
Common questions about QR codes
Do QR codes expire?
The QR code itself does not expire — it permanently encodes its content. However, if the code points to a URL and that URL changes, is deleted or becomes unavailable, the code will stop working. This is why keeping the destination URL stable is important for long-term use.
Can I edit a QR code after creating it?
No. A QR code is a fixed encoding of its content. To change the destination, you generate a new code. If you want the flexibility to change destinations without reprinting, you can use a URL shortener as an intermediary — the QR code points to the shortener URL, and you update the shortener to redirect to the new destination.
Can someone track who scans my QR code?
If the QR code points directly to a final URL, no tracking occurs in the code itself. However, the destination website can log visitors in the normal way. URL shorteners used as intermediaries often provide scan analytics including scan count, time and approximate location.
Why won't my QR code scan?
Common causes: the code is printed too small; insufficient quiet zone margin; low contrast between modules and background; the code was generated from a low-resolution image and looks pixelated; or part of the code is obscured. Try generating the code again at a higher resolution and leaving more margin space.
Related tools and guides
Use Quick QR to create a free QR code for any URL, text, email, phone number, Wi-Fi or contact. For other practical everyday tools, see the full LibraireStudios collection. Browse all guides.
LibraireStudios tools are designed for everyday use. Always verify QR code content before printing or distributing at scale.