How do you write one tag that works on every phone?
A Type 2 tag holding one web address on your own domain, written with its scheme, and nothing else. Every addition to that recipe costs you part of the audience, and the printed fallback covers whatever the tag cannot reach.
The recipe
An NFC Forum Type 2 tag, which is read by essentially every phone with NFC hardware.
One record, of the web address type, holding a short address on a domain you control, written with its scheme.
Nothing else on the tag: no second record, no application record, no text label.
Verified by reading it back and by tapping it on both platforms to see what actually happens.
Why each element
Type 2 because compatibility follows the tag type rather than the brand, and Type 2 is the one with no exceptions worth planning around.
One record because phones act on the first they can handle, so a second record is either ignored or a source of surprise.
A web address because it is the record type acted on most consistently everywhere, and because it needs nothing installed.
Your own domain because it is what lets you change the destination for every tag at once, forever.
The scheme because an address written without it carries no instruction, and each platform then decides for itself what to do.
What to leave out
Wi-Fi credentials, which configure a network on Android and are not acted on the same way by an iPhone.
Records naming an application, which are an Android mechanism and inert elsewhere.
Contact records, unless the handover genuinely happens without a network, since a page serves the same purpose and stays correctable.
And a second record added because there was room. Room is not a reason.
The part the tag cannot do
Some phones have no NFC. Some need an application opened first. Some are asleep, in a metal case, or belong to someone who will not tap an object.
No tag content reaches any of them, so the recipe above is complete and still insufficient on its own.
Print the same address in readable type, and a code beside it where the design allows.
That is not a compromise on the tag. It is the other half of a deployment that reaches everybody.
Frequently asked questions
Which tag type works on every phone?
Type 2, without qualification. Compatibility follows the tag type rather than the chip brand.
Should I add a text record as well?
No. Phones act on the first record they can handle, so a second is ignored or surprising, and it costs space.
Why write the scheme?
Without it the record carries no instruction, and each platform decides for itself. That produces a tag that works on your phone and not on others.
Is a printed fallback really necessary?
Yes. A real minority of any audience cannot use the tag, and no tag content reaches them.