NFC tag generator and writer

• NFC Forum NDEF 1.0 — the message and record format (flags, TNF, short and long records, chunks when reading).
• NFC Forum URI RTD 1.0 and Text RTD 1.0 — links with a prefix code and text with a language code (UTF-8).
• Wi-Fi Alliance Wi-Fi Simple Configuration — network credentials in an application/vnd.wfa.wsc record (Version, Credential, WFA Vendor Extension with Version2).
• vCard 3.0 (RFC 2426) — a contact card as a text/vcard record; tel (RFC 3966), mailto (RFC 6068), sms (RFC 5724), geo (RFC 5870).
• Android Application Record (android.com:pkg) — launches the app or its Google Play page.
• NFC Forum Type 2 Tag — NDEF TLV (0x03, a 1- or 3-byte length, terminator 0xFE); Type 4 — an NDEF file with a two-byte length.

“NDEF area” is the tag's user memory for data. “Max message” already accounts for overhead: a TLV header and terminator on Type 2, Type 5 and MIFARE Classic, and two file-length bytes on Type 4. The table is generated from the same code as the meter.

• Writing and reading tags (Web NFC) — Chrome 89 and newer on Android phones with NFC, only on https pages and in a visible tab. Read-only locking needs Chrome 100+.
• iPhone, Safari, Firefox and desktop browsers do not support Web NFC: the tool builds the same message and gives you .bin, HEX and JSON for a writer app, and a QR code opens this page on an Android phone.
• MIFARE Classic is read and written only by phones with an NXP NFC chip; other Android phones cannot open such a tag.
• iPhone XS and newer open tags with links, phone numbers, email and SMS in the background; iPhone does not handle Wi-Fi, contact cards or text without an app.
• You cannot write to another phone: a phone is not an NFC tag. Android stopped accepting NFC data from other phones in Android 10 (Android Beam), and iPhones never did. You need a tag — a sticker, key fob or card (NTAG213/215/216); to pass the same link, Wi-Fi or contact card to a phone, use the “Send to another phone” block — it shows a QR code.

• Capacity follows typical datasheets: tags from other vendors and reformatted tags may have a different NDEF area.
• When reading, the browser hands over parsed records, not raw tag memory: the bytes on screen are rebuilt per NDEF and may differ from the originals (for example, in link prefix abbreviation).
• Locking a tag is irreversible — neither this tool nor any app can undo it.
• One message holds up to 12 records. The Wi-Fi password never goes into the JSON file; enter it again after a JSON import.
• The password on a tag is stored as plain text: anyone who taps the tag with a phone can read it — use a guest network in public places.

• The message is built and written to the tag right in your browser: records, passwords and read data are not sent to a server. Only a short summary — record types, size, tag model and mode, without Wi-Fi passwords, network names or contact card contents — may go with a request.
• Records are stored in this browser's localStorage; Wi-Fi passwords only when “Remember Wi-Fi passwords in this browser” is on (it is off by default). “Clear all” deletes everything.
• The “Open on a phone” QR code holds only this page's address — none of your records or passwords.
• Analytics receives only the fact of a write, read or export and its format — no content.
• The result reaches us only if you send a request yourself and keep the “Attach the result” box ticked — the form shows exactly what will be sent. Files and images are never sent with a request.