Can an artificer cast spells using a single component from a set of artisan's tools?

Question

Under Tools Required

You produce your artificer spell effects through your tools. You must have a spellcasting focus – specifically tinker’ tools or some kind of artisan’s tool – in hand when you cast any spell with this Spellcasting feature. You must be proficient with the tool to use it in this way.

"Artisan's tool" is singular. But it can refer to a set of objects.

For example:

Weaver's tools include thread, needles, and scraps of cloth.

Weaver's tools are an artisan's tool but does an artificer proficient with them need to hold the needle, thread, and cloth in one hand to cast spells?

Or can an artificer cast spells using a single component from a set of artisan's tools?

For example the party has been striped of all their belongings but not their clothes. Can an artificer with proficiency in weaver's tools tear off a scrap of their clothing and begin casting? What if the rest of the set is on their person?

Answer 1

Artisan tools are themselves a discrete game item.

Tools are described in the PHB:

A tool helps you to do something you couldn't otherwise do, such as craft or repair an item, forge a document, or pick a lock

And artisan tools:

These special tools include the items needed to pursue a craft or trade.

You cannot improvise a piece of special tools needed to pursue a craft and say you have a set of artisan’s tools. The set itself is considered a discrete item by the rules of the game.

In the example you give, no, ripping my shirt does not create weaver’s tools.

Most spell casting foci are intended to be one handed - think rod, wand, crystal ball etc. Having the full set on your person and “wielding” a piece of it is just fine.

In the specific scenario you give, as a DM I might permit an artificer to make an Intelligence (Stealth) check to try to hid all the components of their set of tools somewhere on their person. I'd contest with an Insight check from somebody doing a pat-down search.