QR Codes Explained: What They Store, How They Work, and How to Make One Free

QR codes are on restaurant menus, business cards, product packaging, event tickets, and government forms. Most people scan them every week. Far fewer know how they work, what they can actually store, or how to make one that scans reliably — without handing your data to a third-party tracking service in the process.

What a QR code actually is

A QR code (Quick Response code) is a two-dimensional barcode invented in 1994 by Denso Wave for tracking automotive parts. The "two-dimensional" part matters: unlike a traditional barcode that stores data in one direction (varying widths of vertical stripes), a QR code stores data in both horizontal and vertical directions, which is why it can hold far more information.

The black and white squares encode data using a specific international standard (ISO 18004). The three large square markers in the corners (called "finder patterns") let a scanner determine the code's orientation and size regardless of how the image is held or photographed. The smaller squares scattered inside (alignment patterns) help the scanner decode the code even if the image is slightly distorted or printed on a curved surface.

What can a QR code store?

A QR code can encode any text, up to a maximum of around 3,000 characters (the exact limit depends on the character type and error correction level). In practice, QR codes are used for:

• URLs — the most common use. The code encodes a web address; scanning it opens the URL in the device's browser. Example: https://keptlocal.com/tools/qr-code-generator
• Plain text — any string of characters, such as a Wi-Fi password hint, a product serial number, or a short message
• Email — a mailto: link that opens the device's email app with a pre-filled recipient address (and optionally, subject and body)
• Phone numbers — a tel: link that prompts the device to dial
• Wi-Fi credentials — a structured format (WIFI:S:NetworkName;T:WPA;P:password;;) that iOS and Android can parse to join a network automatically
• vCard / contact info — a structured format that lets users add someone to their contacts by scanning
• App store links — URLs pointing to App Store or Google Play listings

One thing a QR code cannot do on its own: track anything. A QR code is static data. It does not know who scanned it, when, or from where. Tracking happens when the URL inside the code leads to a redirect service (like a link shortener) that logs the visit before sending the user onward. More on this below.

Error correction: why QR codes still scan when damaged

QR codes include redundant data through a technique called Reed-Solomon error correction. This allows the code to be decoded correctly even if part of it is damaged, dirty, or obscured — useful when codes are printed on surfaces that wear, used outdoors, or have a logo placed on top.

There are four error correction levels:

• L (Low) — recovers up to 7% data loss. Best for clean digital displays where damage is unlikely. Produces the smallest, least dense code.
• M (Medium) — recovers up to 15% data loss. The practical default for most use cases.
• Q (Quartile) — recovers up to 25% data loss. Good for industrial or outdoor printing.
• H (High) — recovers up to 30% data loss. Use when you plan to add a logo to the center of the code, or when the printing environment is harsh.

Higher error correction makes the code denser (more squares) and slightly harder to scan at very small sizes. For most uses, Medium is the right balance.

The tracking problem with free QR code generators

Many free QR code generators are businesses built around data collection. They fall into two categories:

Static code generators with analytics dashboards — these generate a unique redirect URL (something like qr.io/abc123) that points to your destination. Every scan goes through their server, logging the scan count, device type, approximate location, and time. This is useful if you genuinely need analytics, but it means every future scan depends on their service staying online, and all scan data belongs to them.

Generators that require account creation — some tools gate QR code downloads or scan limits behind a signup, turning a simple utility into a lead-capture mechanism.

If you just need a QR code that encodes a URL and scans reliably — and you do not need scan analytics — there is no reason to use either. A browser-generated QR code that encodes the URL directly has no redirect layer, no dependency on a third-party service, and no expiry date.

How to generate a QR code without tracking or signup

1. Open a browser-based QR code generator (keptlocal's is at /tools/qr-code-generator)
2. Paste the URL or text you want to encode
3. Choose a size — 300px for digital use, 500px+ for print
4. Set error correction to Medium for general use, High if adding a logo or printing on rough surfaces
5. Download the PNG

The resulting PNG contains the QR code image. Open it in any image editor to resize or modify. No redirect server is involved — scanning the code takes the user directly to your URL.

Getting the size right for print

QR codes scale as vector-like pixel art — they look sharp as long as the squares in the code map cleanly to printer dots. The rule of thumb: the minimum print size is approximately 2cm × 2cm (about 0.8 inches), with a quiet zone (white border) of at least 4 squares wide on all sides. Below that size, older or low-quality scanners start failing.

For business cards: 1.5–2 cm. For A4 posters: 4–6 cm. For billboards or large-format print: aim for a size that can be scanned from the expected viewing distance — the code should subtend about 10° of field of view at the scanner.

When downloading for print use, choose a larger pixel size (500px or above) so that scaling in your design software does not introduce blurring. QR codes should never be resized by a non-integer factor — only scale by whole multiples (2×, 3×, etc.) or keep the original pixel dimensions.

Testing before you commit

Always test your QR code before printing it at scale or distributing it permanently. Scan it with at least two different devices (different phone models, different operating systems). Check that the URL opens correctly, including on mobile — some URLs that work on desktop have mobile redirect issues.

If you add a logo to the center of the QR code, test the modified version. A logo covering more than about 20–25% of the code area will cause scan failures unless you used High error correction.

What happens when the URL in your QR code changes

A static QR code cannot be edited after generation — it is just an image encoding a fixed string. If the URL it points to moves (the page is deleted, the domain expires, the company rebrands), the code breaks.

There are two solutions:

Use a URL you control permanently — the cleanest option. If the QR code points to your own domain, you can update the destination without changing the code. Point the URL to a landing page on your own site, then redirect from there to wherever the content lives.

Use a dynamic QR service — a redirect service that lets you update the destination URL without regenerating the code. This is the right choice when the code is already printed at scale and the destination genuinely needs to change. The trade-off is the service dependency described above.

Common QR code mistakes

• Too small to scan reliably — test at the intended print size before committing to a print run
• Low contrast — dark squares on a light background is the standard for a reason. Coloured codes can work but need testing; pastels on white or white-on-white never work
• No quiet zone — the white border around the code is required. Remove it and many scanners fail
• Linking to a page that does not work on mobile — the vast majority of QR scans happen on phones; test the destination on mobile
• Encoding too much data — very long URLs produce very dense codes that are harder to scan. Use a URL shortener for the destination if the URL is unusually long