Writing an NFC tag

Two writers, and which one you want

Both live under More Tools → NFC Tags. The choice is not about the tag — the same blank tag takes either — but about where the destination is going to live afterwards.

You can also reach the Linxy tag writer from where the item lives. On My Linxy, the NFC Tag action on a Mark or a link writes tags that open it. And when you create something new, choosing NFC Tag on the first step of Create a TouchPoint offers Write it now, with a count of tags to write from this phone once it is created, or Order Linxy Tags for tags that arrive preprinted and marked from the Linxy App’s Marketplace. In that wizard, Network access (Wi-Fi), Contact card, and Plain text or serial are marked Native on a tag: their content is written onto the tag itself, like a standard tag, and changes only when you write the tag again.

There is a third writer for when tags are a production step rather than a handful: the desktop Linxy NFC Encoder, which drives a USB reader at a bench and writes the same two kinds of tag at batch pace. The records are identical — a scanner cannot tell which tool wrote a tag.

For a product that has to prove it is genuine, NFC Tags also has Write Verified authentic tags. These need NTAG 424 DNA chips, which make a new one-time code on every tap, so a copied tag or a copied link fails the check. My Verified authentic tags shows their taps and failed checks, and turns off a lost tag. See Verified authentic tags.

What a Linxy tag actually carries

Every Linxy tag written by the App carries three records: a link that any phone can follow, the same code on its own for the App’s direct route, and an app record that makes an Android tap open Linxy without offering a browser chooser. All three go on together, and the App verifies all three landed before it counts the tag as written.

What is not on the tag matters more. The code is opaque. It does not carry the Mark’s identity, its product code, its name, or anything else about your catalog. Held up to any reader in the world, a Linxy tag says nothing except a string of characters that means something only to the platform.

Writing Linxy tags, step by step

• Choose the Mark. The list is the same one you see under My Linxy, searchable by name. The tag will open this Mark.
• Set the quantity. Type it — any number from 1 to 500, with steppers either side for small adjustments. If you need twelve, enter twelve. There are no brackets to round up to.
• Name them. One tag keeps the name exactly as typed. A batch is numbered from it: Trade show 01, Trade show 02, and so on, going to three digits from a hundred upwards.
• Reserve. The codes are created on the platform at this point. Larger orders are split into several requests behind the scenes, so a hundred tags is a slightly longer wait rather than a refusal.
• Write. Hold a tag, wait for the tick, lift it off, present the next.
• Finish. Any codes you did not use stay valid. Keep writing picks up where you stopped.

The rhythm of the writing step differs by phone, and it is worth knowing which you are on before you start a run of a hundred.

Naming, and why it is the revocation handle

The name is not decoration. It is how you find one tag among five hundred later, in order to revoke that one and leave the rest alone. A batch called Tag 01 to Tag 500 is a batch you can only revoke wholesale.

Every tag is checked before it counts

A tag pulled away part-way through a write can be left holding a truncated message that looks perfectly healthy to a casual reader. To stop that being counted as a good tag, the App reads each tag straight back after writing it and requires both the code and the app record to be present. If either is missing, the tag is reported as having moved away and is not ticked off.

There is one honest exception, on iPhone. A tag is only briefly connected there, and the read-back sometimes cannot run at all. In that case the write is trusted, because the write itself does not return until the system has actually written the tag. A read-back that does run and disagrees still fails the tag. So the check is best described as: always run where it can be, never faked when it cannot.

Writing a standard tag

The standard writer covers seventeen kinds of content, chosen from a picker before you fill anything in. None of them involve Linxy at all, and none of them need an account.

Three of these behave differently depending on the phone, and the form says so as you fill it in. A Wi-Fi tag joins the network on an Android tap; an iPhone shows the network and asks first. FaceTime is an iPhone-only affair. And if you type a Linxy address into Website or URL, the app record is added for you automatically, so an Android tap opens the App rather than a chooser — the form tells you when that has happened.

The form shows the size of what you have built as you type, and whether it fits a small tag. After a write it stays on the form rather than closing, so writing the same content to a second, third and fourth tag is one tap each.

Locking a tag — permanent, and only on one side

The standard writer can seal a tag read-only as it writes it. Locking is irreversible: the tag can never be changed or erased again, on any device, by any application, ever.

Because of that, it is deliberately awkward to trigger. The control does nothing on a normal tap — it tells you to press and hold instead. A long press opens a confirmation asking plainly whether you want the tag locked permanently, and only accepting that arms it. The write button then changes to Write & lock tag so there is no doubt about what the next tag will get. Going back to the type picker disarms it again, so it is never left set from an earlier session.

Lock a tag when it is going somewhere permanent and must not be overwritten by a passer-by with a phone — a fixed plaque, an installed panel, a museum label. Leave it unlocked for anything that might be repurposed, and for every tag in a batch you have not yet placed.

What fits on a tag

The writer checks capacity before it writes, and refuses politely rather than half-writing. When a tag is too small, the message names both numbers — what the tag holds and what the content needs — so the decision about which tag to switch to is made for you.

A small NTAG213 holds 144 bytes, which is ample for a link and comfortable for a Linxy tag, but tight for a full contact card or a Wi-Fi record with a long passphrase. Buying the larger tag is almost always cheaper than discovering the problem halfway through a run.

Symptoms, causes and fixes

Things people commonly get wrong

Related reading: Reading an NFC tag, Secure NFC and standard NFC compared, My Linxy items, Creating from the phone, Verified authentic tags, and When something is not working.