Does a new tag need to be formatted before use?
Usually not. The overwhelming majority of tags are shipped pre formatted and accept a write straight out of the packet. The reliable method is to read one tag from the batch before writing anything, since that single step tells you which of three states you are in.
Three possible states
A tag arriving from a supplier is in one of three conditions, and they behave very differently.
Formatted and empty, which is by far the most common and is ready to write. Formatted with content already on it, which happens with pre encoded tags and means your write will replace something. Or unformatted, which is uncommon and will refuse a write with an error about the format.
Read one tag first
Take one tag from the batch and read it with a tool before doing anything else. Thirty seconds, and it removes all guesswork.
You learn the state, the chip, the tag type and the free space in a single operation. Those four facts determine everything that follows, including whether your content will fit and whether the tags are what you ordered.
Tags from the same batch are almost always in the same state, so one is representative. Tags from different batches are not, which is why this belongs at the start of every production run rather than once ever.
When formatting is genuinely needed
A write that fails with a message about the tag not being formatted, which is unambiguous.
A tag reading as unknown or unformatted despite responding normally, which usually means a previous write was interrupted.
A tag bought as raw stock rather than as NFC tags, since some industrial inlays ship unformatted by design.
Outside those three, formatting is solving a problem you do not have.
Why formatting reflexively is a bad habit
It spends a write cycle for nothing, which matters not at all on one tag and slightly on a large production run.
More importantly, it is an extra operation that can be interrupted, and an interrupted format leaves a worse state than the one you started from. Adding an unnecessary step that can fail is a poor trade against a step that was not needed.
It also masks information. A tag that would have refused a write with a clear error instead gets silently reformatted, and you never learn that your supplier shipped something different from last time.
Frequently asked questions
How can I tell if a tag is formatted?
Read it with a tool. A formatted tag reports its free space and shows either content or an empty message, while an unformatted one is reported as unformatted or unknown.
My write failed with a format error. What now?
Format the tag and write again. If formatting also fails, the tag is either locked or of a family your device does not support, and neither is fixable from your side.
Do pre encoded tags need reformatting?
Only if you cannot overwrite them. A pre encoded tag that is not locked accepts new content directly, and one that is locked cannot be formatted either.
Does formatting a fresh tag do any harm?
Almost none, beyond a wasted write cycle and an unnecessary opportunity for the operation to be interrupted. It is not dangerous, it is simply not useful.