QR Codes Explained: Payloads, Error Correction, and Scan Reliability

The QR code stores a payload

A QR code encodes data in a pattern of modules for a scanner to decode. The Calzivo QR Code Generator offers text and URL modes. In text mode, it encodes the accepted input exactly, including internal spaces. For example, entering Calzivo QR test stores those exact characters. In URL mode, https://example.com/path?q=hello is validated as an absolute HTTP(S) URL and then encoded exactly as entered; it is not normalized, shortened, hosted, redirected, or tracked by Calzivo.

Characters and bytes are different limits

The source field permits at most 2,000 UTF-16 code units. The encoded payload must also be at most 1,024 UTF-8 bytes. These are Calzivo limits, not universal QR capacity limits. Non-ASCII characters can use several UTF-8 bytes, so 1,024 visible characters might exceed the byte limit. Whitespace-only text, leading or trailing URL whitespace, bare domains, relative URLs, and non-HTTP(S) schemes are rejected.

Error correction and the quiet zone

QR error correction adds redundant information that may help a scanner recover data when part of a symbol is damaged. Calzivo uses the library's M setting. It does not make an unreadable print, unsupported scanner, or severely damaged symbol reliably scannable. DENSO WAVE describes a clear quiet zone four modules wide around a QR code; Calzivo sets the library margin to four modules. Keep that border intact instead of cropping it away.

Calzivo output and practical testing

Generation runs in the browser and creates a checked 512 × 512 PNG with black modules on white. The tool checks that the output is a PNG before offering it. These dimensions, colors, error-correction setting, and margin are Calzivo/library choices, not requirements for all QR codes. Before distributing or printing, test the actual downloaded image on relevant devices at the intended physical size and lighting. Preserve contrast and quiet zone; avoid tiny or blurred printing.

A destination is not verified by encoding it

A QR code containing a URL merely conveys that string. Generation does not establish that the destination is safe, still available, controlled by the intended owner, or permanent. Verify a destination independently before sharing it, and re-test the final printed code. Successful image generation is not a promise of successful scanning.