Why SMSTO: instead of sms:?

Wider Android compatibility. The sms: scheme is the RFC standard but a meaningful slice of stock messaging apps mis-parse the body parameter. SMSTO: is the de-facto fallback that just works.

Can it send the SMS automatically?

No. The phone opens a draft; the user sends it. There is no way for a QR scan to silently send a text — that would be a security hole, and platforms do not allow it.

PLATE 06

SCALE 1 : 1

EDITION v0.26.10

FILE KMK·QR·06

FIGURE A · SMS ENCODE

Free SMS QR code generator

Encode a phone number and an optional message body. Scanning opens a pre-filled SMS draft — useful for opt-in promotions, support shortcuts, and check-ins.

Create QR code

process: client-side · zero upload
cost: free · no signup · no expiry
format: PNG · SVG · PDF
license: MIT · open source

§01

Notes on the artifact

An SMS QR encodes the recipient number and a message body. We use the SMSTO: format, which has the broadest stock-app compatibility — better than the official sms: scheme, which some Android stock messaging apps still mishandle.

Common uses include "Text JOIN to opt in" replacements, support shortcuts ("Scan to text our help desk"), and event check-ins where a typed message is awkward. As with the email QR, scanning opens a draft — the user has to send.

Include the country code in the number for international robustness. A bare 10-digit US number works on US carriers but breaks if scanned abroad.

§02

Footnotes & queries

Why SMSTO: instead of sms:?: Wider Android compatibility. The sms: scheme is the RFC standard but a meaningful slice of stock messaging apps mis-parse the body parameter. SMSTO: is the de-facto fallback that just works.
Can it send the SMS automatically?: No. The phone opens a draft; the user sends it. There is no way for a QR scan to silently send a text — that would be a security hole, and platforms do not allow it.

§03

Anatomy of the code

QR ANATOMY FUNCTIONAL REGIONS DRAFTING SCHEMATIC

Every QR code is a part-functional, part-data grid. Three finder patterns at the corners let a scanner lock orientation; an alignment pattern at the bottom-right corrects perspective skew when the code is photographed at an angle. The timing patterns — alternating modules running between the finders — tell the scanner the cell pitch. Format info encodes the error-correction level and mask pattern across 15 bits arranged in an L-shape. The rest of the grid is the payload — data plus Reed–Solomon error-correction codewords. The quiet zone is mandatory whitespace; without four clear modules of margin, scanners reject the code. The detail below the main figure shows the finder pattern's 1·1·3·1·1 ring construction — proportions deliberately chosen so a scanner can recognise the pattern at any rotation, with three patterns at three corners triangulating the code's orientation.

§04