NDEF TNF Types
Type Name Format (TNF) is the 3-bit field in the first byte of every NDEF record header that describes how to interpret the type field. Reference from NFC Forum NDEF v1.0 §3.2.6.
What this reference covers
What this reference does not cover
TNF and the record type tell you how to interpret a record's type field. They say nothing about whether the payload is well-formed, and nothing at all about whether it is trustworthy. NDEF has no integrity or authenticity mechanism in normal use, so every record read from a tag is untrusted input that must be validated before it reaches anything that acts on it.
This page also stops at the record layer. The tag platform beneath it — Type 2, Type 4, or a DESFire file holding an NDEF message — has its own addressing, capability container and access rules, and that is where read or write failures usually originate rather than in the NDEF encoding itself.
Frequently asked questions
What is TNF?
Type Name Format — the 3-bit field in an NDEF record header saying how to interpret the record type: well-known, MIME media, absolute URI, external, unknown, unchanged or empty.
What is a well-known type?
A short type name defined by the NFC Forum, such as U for URI and T for Text. It keeps records compact, which matters on tags with very little memory.
When should I use an external type?
For application-specific records you define yourself, namespaced by a domain you control, so they cannot collide with anyone else's.
What is TNF 0x06 unchanged for?
Chunked records: the middle and final chunks carry unchanged, because the type was declared on the first chunk only.
Can NDEF content be trusted?
No. NDEF provides no integrity or authenticity, so anything read from a tag is untrusted input and must be validated before use.