To rewrite an NFC tag means to overwrite the NDEF data stored on a writable tag, such as a URL or text, with new information, using your smartphone. This does not change the tag's immutable UID, and it only works on tags that are writable, not those locked as read-only.
What it means to rewrite an NFC tag
Rewriting an NFC tag is the process of replacing the existing NDEF (NFC Data Exchange Format) message on a writable tag with new data, like a different website address or a block of text. The tag's unique identifier (UID) is permanently set by the manufacturer and cannot be changed. Only tags that are sold as rewritable can be overwritten; tags that are pre-programmed as read-only or that have been locked cannot be rewritten. NFC tags can be rewritable or read-only; rewritable tags allow users to update the information stored on the tag as needed, while read-only tags come with pre-programmed information that cannot be modified.
What you need before you start
To rewrite an NFC tag you need three things: a writable NFC tag with enough free storage for your new data, a compatible smartphone, and optionally a dedicated writing app. For iPhone, you need an iPhone 7 or later running iOS 13 or later. For Android, you need an NFC-capable phone with NFC turned on in the system settings. Apps like NFC Tools, available on the App Store and compatible from iPhone 7, can read and write NFC tags. Different NFC tag types may have different storage capacities and compatibility with various devices, so it's essential to choose the right NFC tag for your specific needs.
How to rewrite an NFC tag on iPhone
On an iPhone 7 or later with iOS 13+, rewriting an NFC tag uses an app that leverages Apple's Core NFC framework. The documented flow is to detect the tag, connect to it, check its NDEF status, and then write the new NDEF data.
- Open an NFC-writing app that supports Core NFC, such as NFC Tools.
- Hold the top of your iPhone near the NFC tag until the app detects it and connects.
- The app will query the tag's NDEF status to confirm it is writable and has sufficient storage. If the tag has already been used, you may need to erase the existing data before rewriting it; some NFC tag writer apps have options to erase and format tags.
- Select the new data (e.g., a URL or text) and write it to the tag. The app calls the writeNDEF method to complete the operation.
How to rewrite an NFC tag on Android
On Android, you can rewrite an NFC tag using Chrome's Web NFC API or a third-party NFC writing app. The phone must support NFC and have NFC enabled in the system settings.
- Ensure NFC is turned on in your Android phone's settings.
- Open Chrome and use a site that implements the Web NFC API, which creates an NDEFReader object and calls the write() method, or open a dedicated NFC writing app.
- Tap the phone to the writable NFC tag when prompted.
- The write() method writes the new NDEF message to the tag.
How to test your rewritten NFC tag
After rewriting, tap the tag with the same phone you used to write it. If the rewrite succeeded, the tag should trigger the new action, for example, opening the new URL or displaying the new text. If the tag does not respond as expected, the tag may be locked (read-only) or may not have enough storage for the new data. On iPhone, Apple's flow requires the tag to be writable and have sufficient storage; if either condition is not met, the write will fail.
Frequently Asked Questions
Can I rewrite any NFC tag?
No. Only tags that are sold as rewritable can be overwritten. Tags that are locked or pre-programmed as read-only cannot be rewritten.
Why does my rewrite fail?
A rewrite can fail if the tag is locked, if it does not have enough storage for the new NDEF message, or if your phone does not support writing (e.g., an iPhone older than iPhone 7 or an Android phone with NFC disabled).
What is the difference between rewriting and cloning an NFC tag?
Rewriting overwrites the NDEF data on a single tag with new information. Cloning copies the NDEF data from one tag to another writable tag, but cannot copy a protected or locked tag.
Do I need an app to rewrite an NFC tag?
On iPhone, you need a third-party app that uses Core NFC, such as NFC Tools. On Android, you can use Chrome's Web NFC API or an NFC writing app from the Play Store.
What does "NFC tags and readers explained" mean for rewriting?
Understanding the difference between NFC tags (the writable chips) and NFC readers (the phone's hardware) helps you know that the phone must support NFC and the tag must be writable for a rewrite to succeed.
What is the NFC tag on Cash App?
The NFC tag on Cash App refers to a physical tag that can be programmed to trigger a Cash App payment or action when tapped. Rewriting that tag would change the payment link or action it performs. Be cautious when rewriting NFC tags that are associated with payments or security-sensitive information to avoid unauthorized access or tampering.
