What Is a QR Code Generator?

How They Work, Explained

QR Code Fundamentals · 2026 · CustomQRCodeMaker.com

QR codes appear on restaurant menus, product packaging, event tickets, and billboard advertisements across the world. But the tool that creates them, the QR code generator, is less well understood. This guide explains exactly what a QR code generator does, the technical process behind code creation, and why different types of generators produce meaningfully different results.

What a QR code generator actually is
The anatomy of a QR code
How the encoding process works, step by step
Error correction: why damaged codes still scan
Static vs dynamic generators: a critical difference
How visual customisation works without breaking scannability
What a generator outputs and why format matters
Frequently asked questions

1. What a QR Code Generator Actually Is

A QR code generator is software that takes an input (a web address, a block of text, a phone number, a digital business card) and converts it into a two-dimensional matrix barcode that any smartphone camera can read. The term "generator" is accurate in a literal sense: the tool generates a unique visual pattern that encodes your data according to a published international standard, ISO/IEC 18004.

It is worth being precise about what a generator does and does not do. It does not store your data on a remote server in any fundamental sense, at least not for a static code. It performs a mathematical transformation: your input data goes in, a standardised visual pattern comes out. A scanner reading the code later performs the reverse transformation, converting the pattern back into data that the phone can act on.

Dynamic QR code generators do something more, which this guide covers in detail below. But at their core, all QR generators share the same foundational process: encoding input data into a scannable matrix according to the QR standard.

Why the standard matters: QR codes work across billions of different devices and apps because every generator and every scanner follows the same published specification. ISO/IEC 18004 defines the exact structure, encoding rules, and error correction requirements that all compliant QR codes must meet. A generator that deviates from this standard produces codes that may fail on certain devices.

2. The Anatomy of a QR Code

Before understanding how a generator creates a QR code, it helps to understand what the finished code actually contains. A QR code is not a random pattern of black and white squares. Every element of its structure serves a precise, defined purpose.

Element	Location	Purpose
Finder patterns	Three corners	Three bold squares that allow scanners to locate the code and determine its orientation, regardless of the angle at which it is photographed
Alignment patterns	Interior (larger codes)	Smaller squares that correct for perspective distortion when a code is photographed at an angle or printed on a curved surface
Timing patterns	Between finder patterns	Alternating black and white modules that help the scanner determine the size of each individual data module within the grid
Format information	Adjacent to finder patterns	Encoded strips that tell the scanner which error correction level was used and which data mask has been applied
Data and error correction modules	The majority of the grid	The encoded input data, interleaved with error correction codewords that allow reconstruction of damaged sections
Quiet zone	Surrounding border	A mandatory white margin around the entire code, without which scanners struggle to locate the code's edges

A QR code generator must place every one of these elements correctly, in the precise positions required by the standard. The visual appearance of the data modules can vary, which is how customised QR codes are produced, but the structural elements must remain intact and correctly positioned.

3. How the Encoding Process Works, Step by Step

When you enter a URL or any other data into a QR code generator and click create, a multi-stage process executes in milliseconds. Here is what happens at each stage.

Data analysis and mode selection

The generator first analyses your input to determine the most efficient encoding mode. Data consisting only of digits (0–9) uses Numeric mode, which is the most compact. Data using a 45-character alphanumeric set uses Alphanumeric mode. Arbitrary byte data, including URLs and most plain text, uses Byte mode. Kanji characters use a dedicated Kanji mode. This selection directly affects how much data can fit into a given code size: a purely numeric string encodes at roughly three times the density of general byte data.

Data encoding

The input is converted into a binary bit stream according to the rules of the selected mode. The generator adds a mode indicator at the start of the stream and a character count so the decoder knows what type of data to expect and how many characters are encoded. The bit stream is then padded to fill the required data capacity for the chosen version and error correction level.

Error correction codeword generation

Using a mathematical technique called Reed-Solomon coding, the generator calculates a set of error correction codewords from the data bit stream. These codewords are appended to the data. The number of error correction codewords added depends on the error correction level chosen (L, M, Q, or H), which is explained in the next section.

Module placement on the grid

The combined data and error correction bits are placed onto the QR code grid in a specific zigzag pattern defined by the standard, working from the bottom-right corner leftward and upward. The finder patterns, timing patterns, alignment patterns, and format information are laid onto the grid in their fixed positions. These functional modules are never overwritten by data.

Data masking

After placement, the generator evaluates eight different data mask patterns against the populated grid and selects the one that produces the most balanced distribution of dark and light modules. A lopsided distribution of one colour makes scanning harder. The selected mask is XOR-applied to the data modules, and the mask pattern reference is stored in the format information so the scanner knows to reverse it during reading.

Output

The final grid is rendered as an image in the requested format: PNG for screen use, SVG for print and scaling, or PDF for direct press-ready output.

4. Error Correction: Why Damaged Codes Still Scan

One of the most practically important features of the QR standard is its built-in error correction. Scanners can successfully read a QR code even if a portion of it is damaged, obscured, or printed over (for example, by a logo placed in the centre of the code).

This is possible because of the Reed-Solomon error correction codewords generated in step 3 above. These codewords contain enough redundant information to allow the decoder to reconstruct missing or corrupted data modules, up to a limit defined by the error correction level.

QR code generators allow you to choose from four error correction levels:

Level	Label	Max Damage Recoverable	Typical Use
Low	L	~7% of modules	Clean digital environments, small code sizes
Medium	M	~15% of modules	General purpose default for most use cases
Quartile	Q	~25% of modules	Industrial, outdoor, or logo-embedded codes
High	H	~30% of modules	Maximum resilience; codes that will be heavily used

There is a direct trade-off: higher error correction levels require more codewords, which means the data must be distributed across a larger grid. A URL encoded at Level H will produce a visually denser, larger code than the same URL encoded at Level L. Generators that allow logo embedding in the centre of a code typically default to Level H or Q to ensure the covered modules can be reconstructed.

5. Static vs Dynamic Generators: A Critical Difference

Not all QR code generators work the same way once the code leaves the tool. This is the most significant practical distinction a user should understand.

Static QR Code Generators

A static generator encodes your destination data directly into the QR code pattern. The URL or text is permanently baked into the modules. Once the code is generated and printed, the destination cannot be changed.

If the linked page moves, the page is deleted, or you want to send users somewhere different, the code is broken and cannot be recovered. You must generate a new code and reprint any materials that carry the old one.

Static codes are free to generate with most tools, require no ongoing account or subscription, and have no scan limits. They are appropriate for stable, permanent destinations.

Dynamic QR Code Generators

A dynamic generator encodes a short, fixed redirect URL into the QR code pattern. That redirect URL points to the generator's own servers, which then forward the scanner to your actual destination.

Because the redirect is controlled by the generator platform, you can change the final destination at any time without changing or reprinting the code itself.

This architecture also enables scan analytics. Because every scan passes through the platform's servers, the platform can log the time, geographic location, device type, and operating system of each scan.

	Static	Dynamic
Destination editable after printing	No	Yes
Scan analytics	No	Yes
Requires ongoing subscription	No	Yes
Codes stop working if subscription ends	No	Yes
Data encoded into code itself	Yes	No (redirect URL only)
Appropriate for permanent destinations	Yes	Yes
Appropriate for campaigns with changing destinations	No	Yes

6. How Visual Customisation Works Without Breaking Scannability

Many QR code generators offer visual customisation options: colours, rounded or shaped modules, custom eye designs, and logo placement. Understanding how this works helps explain why some customised codes scan reliably and others do not.

Colours and contrast

The QR standard requires sufficient contrast between the dark modules and the light background for scanners to reliably distinguish them. Generators that allow colour customisation should maintain this contrast ratio. Very dark backgrounds combined with dark modules, or pastel-on-white combinations with insufficient contrast, produce codes that scan inconsistently. The safest approach is dark modules on a light background, though the modules themselves can be any dark colour and the background any light colour.

Module shape

The standard specifies that modules should be square, but it does not prohibit scanners from reading codes with rounded or otherwise shaped modules, provided the centre-point of each module remains in the correct grid position. Most modern smartphone cameras handle shaped modules without difficulty. Generators that move or significantly resize modules to create visual effects can compromise scannability.

Logo placement

A logo placed in the centre of a QR code obscures the data modules beneath it. This is intentional use of the error correction capacity described in section 4. A logo that covers up to approximately 30% of the code area can be accommodated at error correction level H. Generators that offer logo placement should automatically set the error correction level appropriately. A logo that exceeds this coverage threshold will produce a code that fails on at least some scanners.

Quiet zone

The white border around the code is not decorative. It provides the visual context scanners need to locate the code's edges. Generators that allow the quiet zone to be reduced below the recommended four-module width are creating codes that will fail in environments with visually busy backgrounds, such as printed materials with adjacent text or imagery.

7. What a Generator Outputs and Why Format Matters

Once the code is generated, the output format determines how the code can be used and how well it will reproduce in different contexts.

PNG

A rasterised image format of fixed pixel dimensions. A PNG generated at a small size will appear blurry or pixelated if enlarged. Appropriate for digital use: websites, email, and social media.

SVG

A vector format that encodes the QR code as mathematical shapes. Can be scaled to any size without quality loss. The correct format for print workflows or unknown sizes.

PDF

Packages the QR code in a print-ready document, often with correct bleed and crop marks. The most appropriate format for sending directly to a commercial printer.

EPS

An older vector format used by some legacy print applications. Functionally similar to SVG for print purposes but less universally supported in modern design software.

For any physical print application, requesting an SVG or PDF output from the generator is strongly recommended. A PNG generated at screen resolution will produce a visibly degraded result when printed at commercial quality.

8. Frequently Asked Questions

What is the maximum amount of data a QR code can hold?

A QR code can encode up to 7,089 numeric characters, 4,296 alphanumeric characters, or 2,953 bytes of binary data in a single code at the largest version (Version 40) and lowest error correction level (L). In practice, most QR codes used in marketing encode a short URL of 30–80 characters, which requires a relatively small and simple code. Encoding very large amounts of data produces a dense, difficult-to-scan code that is impractical for most real-world applications.

Do QR codes expire?

Static QR codes do not expire. The pattern is self-contained and will scan correctly indefinitely, regardless of whether the destination URL still exists. Dynamic QR codes are tied to a redirect service and will stop functioning if the subscription to that service ends or if the redirect is manually deactivated.

Why does my QR code sometimes fail to scan?

The most common causes are insufficient contrast between modules and background, a quiet zone that has been cropped too narrow, a logo that covers more than the error correction capacity allows, a very small printed size, and printing on a highly reflective or textured surface. Generators that produce SVG files and set error correction to Level H for logo-embedded codes avoid most of these failure modes.

What is the difference between a QR code and a barcode?

A traditional barcode encodes data in a one-dimensional pattern of vertical lines that varies in width and spacing. It can only encode data horizontally, which limits its capacity. A QR code encodes data in two dimensions, both horizontally and vertically, which is why it can hold significantly more information in a smaller physical space, and why it can still be read even when partially damaged.

Can a QR code contain malware?

A QR code cannot itself contain executable code. It encodes data, most commonly a URL. The risk is that a QR code can encode a URL pointing to a malicious website, just as a typed or printed URL can point to one. Scanners that display the decoded URL before opening it give users an opportunity to verify the destination before proceeding. Generating QR codes from reputable tools and verifying that the encoded URL is correct before publishing the code are standard safety practices.

Does the visual appearance of a QR code affect its data?

No. The visual customisation applied by a generator (module shapes, colours, logo placement) does not change the underlying encoded data. The data is determined entirely by the input entered at generation time. Visual customisation only affects the rendered appearance of the modules, not the bit stream they represent.

Published by CustomQRCodeMaker.com · Educational content · 2026