QR code scanner and reader

How reading a QR code works

Decoding is the reverse of generating. The reader takes the pixels of your image, locates the three large finder patterns in the corners to work out where the code sits and how it is rotated, then samples the grid of modules back into a stream of bits. Those bits are protected by Reed–Solomon error correction, so even if part of the code is smudged, covered by a logo or slightly torn, the decoder can reconstruct the missing data and still return the exact payload. What comes out is a short opaque string — a URL, a vCard contact, Wi-Fi credentials, geo coordinates or just plain text. This tool uses jsQR, a pure-JavaScript port of the reference decoder, and runs it entirely on the pixels already in your browser; nothing about the image or its contents is sent anywhere.

What decodes cleanly — and what doesn't

Both photographs and screenshots read reliably when the code is fully in frame, the contrast is reasonable, and the rotation is under roughly 30 degrees. The reader downscales large images before decoding and tries both normal and inverted colours, so a light-on-dark code still works. Codes fail to read for predictable reasons: the image is cropped so a finder pattern is cut off, motion blur or a steep angle has warped the grid, the contrast is too low, or it is a Micro QR symbol — a smaller variant this engine does not yet support. Standard QR symbols across versions 1–40 and every error-correction level are covered. If a scan fails, re-crop to include the whole code with a little margin, or retake the photo square-on under even light.

Privacy and related tools

Because decoding happens locally and the strict content-security policy blocks outbound network calls, even sensitive payloads — a Wi-Fi key, a signed or single-use URL, a contact card — never leave your device. That is the practical difference between a client-side reader and a phone app or website that uploads the image to "scan" it. Need to go the other way and make a code? The QR code generator builds URL, Wi-Fi, contact and email codes. To pull text out of a regular photo or scan rather than a QR code, the image-to-text (OCR) tool reads printed and handwritten characters, and barcode generator covers retail and shipping symbologies.