How do I know if a tag is locked before writing?
Read it first. A reading tool reports whether a tag is writable alongside its chip and free space, and doing that before a batch prevents the only failure in this area that cannot be undone. It costs seconds and it is the check people skip.
Read before you write
A tag reports its own writability. The information sits in the tag and any tool that shows technical data will tell you, without changing anything.
This matters because the alternative is finding out by failing, and by then you may have written half a batch or wasted an hour on a delivery that was never usable.
It also settles the question no amount of retrying will answer. A protected tag refuses in the same way every time, so persistence is not a diagnostic.
The states you might find
| Reported state | What it means | Recoverable |
|---|---|---|
| Writable | Normal, nothing set | Not applicable |
| Read only | Lock bits set, permanently | No |
| Password protected | Writing needs the key | Only with the key |
| Not formatted | No NDEF structure yet | Yes, format it |
| No tag type reported | Not a Forum tag type | No, wrong product |
Only two of those five are dead ends, and telling them apart from the other three takes one read.
Checking a batch properly
Take samples from different parts of the delivery rather than the top of one stack, since a mixed shipment is a real possibility.
Check enough to know the proportion. Ten tags out of a thousand tells you whether you have a problem, and one tag does not.
Do it before writing anything at all. A batch you have started writing is harder to return, and a locked tag is not returnable in any circumstance.
Record what you found per delivery, with the date. Two numbers over two deliveries tell you whether something changed at the supplier.
Making it a habit
Read one tag from every delivery, every time. Not just the first delivery, which is the one a supplier pays attention to.
Read one tag before every writing session, even from stock you have used before. Boxes get mixed and labels get swapped.
And keep one unwritten tag from each batch, labelled with the date, as a reference. Comparing a suspect tag against a known good one from the same batch answers most questions immediately.
This is a minute of work that prevents the two outcomes in this section that no tool, application or manufacturer can reverse.
Frequently asked questions
Does reading a tag change anything?
No. Reading powers the tag and asks it to recite what it holds, so nothing is written and nothing is consumed.
Can a tool be wrong about writability?
It reports what the tag says about itself, which is reliable. What varies is how clearly different tools present it.
What if the tool shows no tag type?
That points at a chip which is not an NFC Forum tag type. It is a different product rather than a protected tag, and no phone will read it as a tag.
Should I check every tag in a batch?
Before installation, yes, wherever reaching the tag again is expensive. For the protection question, a sample from several parts of the delivery is enough.