How do you build a tag driven board game aid?
By tagging the questions that stop play rather than the pieces. A card on the table per recurring rule query, each opening the relevant page, removes the search through a rulebook that everybody dreads. Tagging the pieces themselves sounds better and does almost nothing.
The problem worth solving
Games stop for one reason more than any other: somebody has to look something up, and the rulebook has no index worth the name.
Five cards on the table, each opening the page that answers a question this group keeps asking, removes that entirely. It is a small project with a disproportionate effect.
Which five is specific to the group. Watch one session, note what gets argued about, and tag those.
Why tagging the pieces fails
The obvious idea is a tag in every piece, so the phone knows what it is looking at. It disappoints for reasons that are structural rather than fixable.
A phone reads one tag at a time, held within a couple of centimetres. A board is a flat surface covered in pieces, which is the worst possible arrangement for that.
And a tag has no idea where it is. It reports what is written on it, not which square it sits on, so the position that makes a board game a board game is invisible.
Commercial games that read pieces use a reader under the board, one per position, which is a different machine from a phone.
What to build
Cards, printed with the question, tagged on the back. Each opens the relevant part of the rules, whether that is a page you host or a section of a reference somebody already maintains.
Keep them with the game, in the box. A tool that lives elsewhere is a tool nobody has when the argument starts.
Write them unlocked, since the first version will be wrong about which questions matter.
Take NFC Tools. On iOS it requires an iPhone 7 or later running iOS 15.6 or later, and the app must be launched manually. Background reading is available from the iPhone XS and XR onwards.
Designing your own game
For a game you are writing, tags do something more interesting: they hold information a player is not meant to see until a moment arrives.
A sealed envelope does this with paper. A tag does it with a page that can be longer, can include audio, and cannot be peeked at by holding it to the light.
It cannot stop a curious player tapping early, which is the same limitation the envelope has, and the same social contract solves it.
Frequently asked questions
Can a phone tell which pieces are on the board?
No. A phone reads one tag at a time at close range, and a tag has no notion of where it is.
How do commercial games do it then?
With a reader under the board, one per position. That is dedicated hardware rather than a phone.
What should the cards point to?
The specific part of the rules your group argues about, not the rulebook as a whole. The point is skipping the search.
Can a tag hide information until later?
It can hold something nobody has read yet, like a sealed envelope. It cannot stop someone tapping it early.