The TigerTag chip (RFID/NFC format)

Physical layer

Property	Value
Chip family	NTAG213 / 215 / 216 (NFC Forum Type 2)
Recommended form factor	25 mm round sticker (other shapes work)
Payload	144-byte NDEF payload — sized to fit the small NTAG213; larger chips leave unused space
Official branded chips	Produced as NTAG215 — the extra memory maximizes end-of-life reuse (standard NDEF objects) so the chip never becomes e-waste
Authentication	None — openly readable
Write lock	None — chips ship unlocked; the user can rewrite them, including migrating to another protocol entirely
Reserved area	64 bytes at the end of the payload — pages 0x18–0x27, leaving 80 bytes of data. On a standard TigerTag they are free for community add-on functions; on a TigerTag+ they carry the origin signature, 32 bytes of R and 32 of S (byte-level layout: TigerTag-RFID-Guide)
Chips per spool	Two, placed on opposite sides
Readable by	Any NFC smartphone, ACR122U-class USB readers, TigerPOD

This is the deliberate opposite of manufacturer tags (Mifare Classic with derived keys, AES sectors, RSA signatures — see compatibility): a TigerTag chip hides nothing.

Think of the chip as long-term cold storage for the spool’s identity: the data lives on the chip itself, offline, for years — no server, no account, nothing required to keep it alive. The online layer (reference database, cloud sync) only ever adds freshness on top.

Why every spool carries TWO chips

Two chips, on opposite sides of the spool — it looks redundant, it’s actually the smartest detail of the format:

• Printers share readers. A machine typically has one RFID reader for two spools (left/right); a Bambu Lab AMS has 2 readers for 4 slots; on a Snapmaker the spool sits either side of the printer. With a chip on each side, whatever the slot, one chip always faces the reader.
• No flipping when hand-scanning. However you grab the spool, a chip is facing you — tap and done.
• Scan in place. A spool mounted on an AMS Lite, the side of an Elegoo Centauri Carbon or a FlashForge can be scanned without pulling it out.
• Integrator freedom. A filament-dryer maker just puts the reader wherever fits — left or right for a single-spool dryer, between the two spools for a dual — and it always works.
• Redundancy. If one chip stops answering, the other still identifies the spool — and serves to repair the broken one.
• Double the harvest. At end of life, every kilo of filament printed leaves you two reusable NTAG chips for DIY projects (zero e-waste).

A few implementation details:

• The two chips are fully independent — each has its own UID; there is no shared antenna. They are written together as a pair (Twin Tag) and kept identical for the spool’s whole life, down to the grams left — and always counted as one spool.
• On factory spools, the chips ride a carrier: a strip whose two ends fold over the cardboard core (one chip per end), held with industrial 3M adhesive (468MP / 200MP) — the operator peels and sticks, nothing else changes on the line. The carrier design is public and printable at home.

The carrier, bare: the two independent antennas are plainly visible — one per folded end, each with its own UID.

Payload

The 144-byte payload encodes the spool’s universal identity — brand, material, aspect/color, type, diameter, print settings — as IDs resolved against the shared reference database.

TODO: byte-level field layout. The canonical specification lives in TigerTag-RFID-Guide; this page should summarize it (offsets, versioning, ID tables) once finalized there. Never document offsets here from memory.

Reading and writing

Tool	Read	Write
Tiger NFC Connect (mobile NFC)
Tiger Studio + ACR122U/TigerPOD	auto-opens the spool on scan	guided, UID-checked write
JS SDK (tigertag on npm)
Python SDK

Versioning

The payload carries a format version (reference table id_version), so readers can stay compatible with older chips.

---

Related: TigerTag, SDKs, Compatibility