Wi-Fi, vCard and other QR payload builder

Notes per type

• Wi-Fi: iPhone joins the network directly from the Camera app. The security field must match the router; choose nopass for open networks. Hidden networks need H:true. The Wi-Fi QR code page covers escaping and the cases where iPhones ignore the code.
• vCard: keep it to the fields you need; every field adds modules. Version 3.0 is the safest choice for phones. The vCard QR code page lists which fields phones actually read, and the MeCard QR code page covers the smaller one-line format and where iPhone support falls short.
• SMS: SMSTO:number:message is the widely supported form. The message is prefilled; the user still has to tap send. More on SMSTO versus sms: in the SMS QR code page.
• Email: a mailto: link with subject and body encoded. Line breaks in the body become %0A. The email QR code page explains the encoding and why the old MATMSG format is best avoided.
• Phone: international format with a plus sign, no spaces. The phone QR code page shows how iPhone and Android handle the tel: link.
• Location: geo:lat,lon opens the maps app. Coordinates in decimal degrees. The location QR code page compares geo: with Google Maps and Apple Maps links.
• Calendar: a bare VEVENT works on iOS and most Android scanners. Times are written in local time; add a Z for UTC if the audience spans time zones. The calendar event QR code page explains how to write the dates so they land in the right time zone.

For how each of these strings is turned into modules, see QR code encoding explained.