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What is stored on a tag

OpenPrintTag is an open format for describing a filament spool on an NFC tag. The station writes a spool's details from Spoolman to the tag, so the spool carries its own description and the station recognises it when you put it down.

What the station writes

When you write a tag, the station builds the tag content from the Spoolman spool you chose.

On the tag Taken from Spoolman Note
Unique ID of this tag's content Spool extra field opentag_instance_uuid, if it exists The station creates one if the spool has none. Used to link tag and spool.
Kind of material — Always "filament"
Filament name Filament name Left out if empty or longer than 63 bytes
Brand Vendor name Left out if empty or longer than 31 bytes
Material Filament material Left out if empty or longer than 7 bytes
Material type Filament material Only when it is exactly PLA, PETG, TPU, ABS, ASA, PC, PCTG, PP, PA6, PA11 or PA12
Maker's article number Filament article number Left out if empty or longer than 16 bytes
Nominal filament weight Filament weight
Filament weight of this spool when full Spool initial weight
Empty spool weight Spool empty weight; if not set, the filament's; if not set, the vendor's
Density Filament density
Diameter Filament diameter Must be a whole number of micrometres, for example 1.75 mm
Colour Filament colour 6 or 8 hex digits. A filament with several colours gets no colour on the tag.
Filament used so far Spool used weight Required

Text that is too long is left out, not shortened. Before you write, the review page lists every detail that will be left out ("Not written: …" on the touchscreen, "Not written to the tag:" in the browser). See Details that are not written to the tag. A plain letter or digit is one byte; an accented or non-Latin letter counts as two or more. Archived spools cannot be written to a tag.

What stays only in Spoolman

Print and bed temperatures, price, location, lot number and comments are not written to the tag.

The remaining weight on the tag is a copy from the moment of writing. Saving a new weight to Spoolman after weighing does not change the tag. To bring the tag up to date, use UPDATE TAG (browser: Update tag): see Write or update a tag. If nothing has changed, the station says Tag already up to date and writes nothing.

How a tag is linked to a spool

After the tag is written and checked, the station saves the link on the spool in Spoolman, in one or both of these places:

Where in Spoolman Contains When
The spool's tag list The tag's permanent ID Spoolman 0.27 or later
Spool extra field nfc_uid The tag's permanent ID When the extra fields exist
Spool extra field opentag_instance_uuid The unique ID the station wrote to the tag When the extra fields exist

When you place a tag, the station looks for the spool that holds these values, starting with Spoolman's tag list. That is how it knows which spool is on the scale. On Spoolman older than 0.27 both extra fields must exist before you write the first tag; on 0.27 or later they are optional. See Required extra fields. Without the extra fields, the unique ID is kept only on the tag and on the station.

A tag with valid OpenPrintTag data but no matching spool shows Not linked to a Spoolman spool yet. Use LINK TO A SPOOL (browser: Link to a spool).

Reading and clearing

  • The station reads a tag by itself when you place it. Reading never changes the tag.
  • It writes only after you confirm on the screen. After writing, it reads the whole tag again and compares it before it reports success.
  • Clearing sets the data area to zeros and removes the link from the spool in Spoolman. The spool itself stays in Spoolman. The tag's permanent ID does not change. See Clear and reuse a tag.