Is the Steel Defender's Force Empowered Rend affected by items that add +1 to Spell attack rolls?

Question

Do items that affect an Artificer's spell attack modifier also affect the Steel Defender's actions that use said spell attack modifier?

As an example, my current level 4 Artificer has

• +4 INT
• +2 Prof bonus
• +1 from an All-Purpose Tool
• +1 from the Enhanced Arcane Focus

So a +8 to spell attacks. Does this mean that Force Empowered Rend also has +8?

See Steel Defender's Force Empowered Rend Tasha's Cauldron of Everything (pg. 19):

Melee Weapon Attack: your spell attack modifier to hit, reach 5 ft., one target you can see. Hit: 1d8 + PB force damage.

Artificer's Enhanced Arcane Focus Infusion Tasha's Cauldron of Everything (pg. 21):

While holding this item, a creature gains a + 1 bonus to spell attack rolls. In addition, the creature ignores half cover when making a spell attack. The bonus increases to +2 when you reach 10th level in this class.

All-Purpose Tool Tasha's Cauldron of Everything (pg. 119):

Wondrous item, uncommon (+1), rare (+2), very rare (+3) (requires attunement by an artificer)

While holding this tool, you gain a bonus to the spell attack rolls and the saving throw DCs of your artificer spells. The bonus is determined by the tool's rarity.

Answer 1

No, the Steel Defender does not benefit from these bonuses.

All-Purpose Tool states:

While holding this tool, you gain a bonus to the spell attack rolls and the saving throw DCs of your artificer spells

The All-Purpose Tool only increase your spell attack modifier when you are casting an artificer spell.

Enhanced Arcane Focus Infusion states:

While holding this item, a creature gains a +1 bonus to spell attack rolls.

This infusion adds +1 to your spell attack rolls, but the Steel Defender is an entirely different creature that is not making spell attack rolls.

Both of these items increase your bonus to hit, but only under certain circumstances. The Steel Defender's bonus to hit is equal to your spell attack modifier at the time it is making the attack, and at this time your spell attack bonus is unmodified by the All-Purpose Tool and Enhanced Arcane Focus Infusion.

Answer 2

The all-purpose tool definitely doesn't work.

Since the tool only grants a bonus to the spell attack rolls "of your artificer spells", and your Steel Defender's melee attack is not an artificer spell, it definitely doesn't apply.

The Enhanced Arcane Focus infusion might work.

Since the enhanced focus infusion says "while holding this item, a creature gains a +1 bonus to spell attack rolls" and the creature holding it is you, it probably doesn't work, but on the other hand it's a generic bonus to the stat that the Steel Defender uses for its attack rolls, so it's hard to say no.

In general, I tend to lean in favor of the players when a question like this comes up, and if it's just a +1, I'm not too terribly concerned about the balance implications, so I'd be inclined to allow it.

I don't know if a steel defender can 'hold' an item to gain the bonus itself, if you decided to got that direction, but it sounds like that isn't the question at hand anyway.