What Information Can a QR Code Contain?

Every QR code contains text, nothing more. What makes one code open a website and another join a WiFi network is the format of that text. Phones recognise a handful of standard formats and offer a matching action.

Below are the formats that work on today's phones, what each looks like inside the code, and what doesn't fit in a QR code at all.

It's always text

A QR code stores a sequence of characters. When a phone scans it, the camera app looks at the start of that text. If it begins with https://, it's a link; if it begins with WIFI:, it's a network; if it begins with BEGIN:VCARD, it's a contact. Anything it doesn't recognise is shown as plain text.

That also means you can see exactly what a code does before acting on it, by reading the raw text with a QR decoder.

Formats phones recognise

The QR Code Generator builds each of these for you, including the escaping rules that trip people up, such as a semicolon inside a WiFi password. Guides for the most common types: WiFi, website links, contact cards, email, phone, SMS, WhatsApp and Google Maps.

Links that open apps

Many “app” QR codes are ordinary web links that an app has registered to handle. A WhatsApp code contains https://wa.me/447700900123, which opens WhatsApp if it's installed and WhatsApp's website if not. Google Maps, app store and social-profile codes work the same way. Because they're normal links, they degrade gracefully on phones without the app.

Formats with patchy support

Calendar events and geo: locations are standard formats, but not every camera app acts on them: some just show the text. For locations, a Google Maps link is the more dependable choice. For events, test on both iPhone and Android before printing.

How much can a QR code hold?

The absolute maximum is 2,953 bytes of text (or 7,089 digits) in the largest version at the lowest error correction. In practice the limit is how dense a code you're willing to print and scan. A few rules of thumb:

• Under about 100 characters: small, open codes that scan instantly. Most links, WiFi codes and phone numbers are here.
• A few hundred characters, such as a full vCard with an address: the code gets noticeably denser and needs printing larger.
• Over 1,000 characters: technically possible, but hard to scan with a phone. Put the content on a web page and link to it.

Non-English text uses more space: accented letters take two bytes in UTF-8, and many Asian scripts and emoji take three or four.

What a QR code can't contain

• Files, PDFs, images, audio or video. Upload them somewhere and encode the link.
• Anything that changes after printing, such as a price or an opening time. The code shows what was encoded on the day it was made.
• Hidden or executable content. A code can't install software or run anything on its own; at most it contains a link that the phone asks you about.
• Secrets. Anything in a code, WiFi passwords included, can be read by anyone who scans it.

Checking a code's content

Before printing a batch, it's worth confirming the content is well-formed: a WiFi code with a missing network name, or a link with a space in it, will scan but won't work. The QR Validator decodes an image and checks the content against the rules for its type.