NFC Tag NDEF Writer Simulator
Simulate writing NDEF messages to NFC tags before touching a physical card. Compose Text, URI, and Smart Poster records, select a target tag, and see exactly how much memory your message consumes — including NDEF TLV overhead, CC bytes, and lock bytes. No guessing, no wasted tags.
1. Select Target Tag
2. Compose Records
3. Memory Simulation
How to Use
1. Select your target NFC tag type — each has different usable NDEF capacity.
2. Add Text, URI, or Smart Poster records to build your NDEF message.
3. Watch the memory bar fill in real time. Green = fits, Yellow = tight, Red = over capacity.
4. Copy the hex and test it in our NDEF Parser or write it to a physical tag.
Related Tools
NDEF Message Parser — Decode hex NDEF | NFC Tag Capacity Calculator — Full tag comparison | MIFARE Access Bits — Sector trailer perms
NDEF Message Construction
NDEF (NFC Data Exchange Format) is the standard data format for NFC tags, defined in NFC Forum RTD specifications. NDEF messages contain one or more NDEF records, each carrying a typed payload. Understanding the NDEF binary format is essential for developing NFC tag writing applications.
NDEF Record Structure
Each NDEF record has a header with flags (MB, ME, CF, SR, IL, TNF), followed by type length, payload length (1 or 4 bytes depending on SR flag), optional ID length, type field, optional ID field, and payload. The TNF (Type Name Format) field indicates the type system: 0 = empty, 1 = NFC Forum well-known type (like "U" for URI, "T" for text), 2 = Media-type (MIME), 3 = Absolute URI, 4 = NFC Forum external type. The MB (Message Begin) and ME (Message End) flags mark the first and last records in a message.
Common Record Types
URI Record (TNF=1, type="U"): Encodes a URI with a prefix byte (0x00=none, 0x01=http://www., 0x02=https://www., etc.) followed by the URI string. Text Record (TNF=1, type="T"): Encodes text with a language code prefix. Smart Poster (TNF=2, type="Sp"): Contains nested URI, text, and optional action records. vCard Record (TNF=2, type="text/vcard"): Stores contact information. Android Application Record (TNF=4, type="android.com:pkg"): Launches a specific Android app. Use our NDEF Parser to decode existing NDEF messages.
Write Your NDEF to Physical Tags
The simulator shows you the exact bytes - a reader and blank tags let you see them land on real hardware.
NTAG215 Sticker Pack (50 tags) (~$7) — Blank 504-byte stickers, the most common target for the NDEF messages this tool builds.
ACR122U NFC Reader (~$40) — USB contactless writer to program the tags from your computer (~$40).
Disclosure: As an Amazon Associate, CardWise earns from qualifying purchases at no additional cost to you. This does not affect our recommendations.