QR Readability Tester

The readability score is a 0-100% rating that predicts how reliably a QR code will scan across different devices and conditions. It is calculated from four weighted factors: module size (30%), contrast ratio (30%), quiet zone adequacy (20%), and image resolution (20%). Scores above 80% indicate excellent reliability, while scores below 40% suggest the QR code may fail to scan in many real-world scenarios.

Module size is measured in pixels per module by calculating the distance between the centers of the top-left and top-right finder patterns and dividing by the number of modules between them (which depends on the QR version). A module size of 2.5 pixels or larger is considered good for reliable decoding.

A contrast ratio of 80 or higher (on a 0-255 luminance scale) is recommended for reliable scanning. Values below 50 may cause decoding failures, especially on devices with lower-quality cameras or in suboptimal lighting. Pure black on pure white produces a contrast ratio close to 255, which is ideal.

The quiet zone is the blank margin around a QR code, required to be at least 4 modules wide on all sides. The tool checks each of the four sides by sampling luminance outside the QR code boundary. If fewer than 4 sides have adequate quiet zone, scanners may fail to locate or decode the code, especially in busy layouts.

Yes, the tool works with any clear image of a QR code in PNG, JPEG, WebP, GIF, or BMP format. The image should show the QR code at a reasonable size — at least 150 pixels in its smallest dimension for reliable analysis. Very small or highly compressed images may produce inaccurate readability scores.

Yes. The tool attempts to decode the QR code in both standard and inverted modes. If the code requires inversion, the result is noted, and a small score penalty is applied since some scanners may not support inverted codes. For maximum compatibility, standard dark-on-light colors are recommended.

The readability score is based on established QR code scanning principles and pixel-level analysis of the actual image. However, real-world scanning reliability also depends on factors the image alone cannot measure: lighting conditions, scanner camera quality, surface curvature, and potential damage to the printed code. Use the score as a guide, not a guarantee.

For smartphone scanning, a module size of at least 0.8 pixels in the image is the absolute minimum for jsQR to detect the code. For reliable real-world scanning, 2-3 pixels per module is recommended. For print, the physical module size should be at least 0.3 mm for smartphone scanning at close range.

Image resolution directly affects how cleanly individual modules can be separated. Low-resolution images cause module boundaries to blur together, making it difficult for the decoder to distinguish adjacent dark and light modules. Higher resolution images (500+ pixels in the smallest dimension) produce more accurate decode results.

Absolutely. Product packaging QR codes should be tested thoroughly before printing. Upload a mockup or final artwork and check the readability score. Pay special attention to the contrast factor (if using brand colors instead of black/white) and the quiet zone (if the code is near package edges or folds).

No. All image processing and pixel analysis happens entirely in your browser using client-side JavaScript and the jsQR library. Your images and decoded data never leave your device. This makes the tool suitable for analyzing proprietary designs, confidential documents, and sensitive QR codes.

An inverted QR code has light modules on a dark background (e.g., white squares on a black background), which is the opposite of the standard dark-on-light design. Some QR code scanners can decode inverted codes, but many cannot. The tool tests both modes and notes if inversion was required.

There is no limit. You can test as many QR code images as you like. Each analysis runs independently, and you can click "Test Another" to restart the process. There are no sign-ups, usage quotas, or advertisements.

Images up to 20 MB are supported. For best results, use images where the QR code occupies a significant portion of the frame and the resolution is at least 300x300 pixels. Very large images (over 4096 pixels) are automatically scaled down for processing.

The tool can decode QR codes with minor damage thanks to Reed-Solomon error correction. However, readability analysis of damaged codes will reflect the reduced module clarity and may recommend improvements. Severely damaged codes may not decode at all, in which case the tool reports an error.