Last night's session began with one PC escorting a prisoner (1). The PC (an artificer) wanted to have the prisoner in hand manacles, and further to have cast arcane lock on said manacles, both of which I allowed.

As described in the PHB, manacles have

Breaking them requires a successful DC 20 Strength check. Each set of manacles comes with one key. Without the key, a creature proficient with Thieves' Tools can pick the manacles' lock with a successful DC 15 Dexterity check. Manacles have 15 Hit Points.

Arcane Lock says:

While affected by this spell, the object is more difficult to break or force open; the DC to break it or pick any locks on it increases by 10.

The spell is easy to apply to a strength check attempt to break them: +10 to the DC is now DC30. Likewise picking them is a now a DC25 Dexterity check.

However, the manacles explicitly have both a vulnerability to a Strength check and a listed hp as an object. Presumably one would use the strength check for an attempt which might shatter them at one go but which, if failed, would do minimal damage. The hp, on the other hand, would be relevant for several attacks which sought to accumulate enough damage to break them. It is worth noting that the listed hp for the manacles are well above the standard for an object of their size (see DMG 246, 247), which makes sense as their primary function is to not be broken.

Spells do what they say they do; my interpretation of "While affected by this spell, the object is more difficult to break or force open;" is that while the spell specifies the increase in DC for a strength check to break something, it would also increase the difficulty of breaking it by applying damage - but leaves the adjudication of that to the DM.

Others disagree, and contend that because the spell only mentions strength checks that is the only protection it applies. Answers to this question should assume that the spell does in fact protect against damage; frame challenges are useful only inasmuch as they advance arguments beyond what is already available at the linked questions (and @Darth Pseudonym, you are welcome to frame challenge - so long as you develop your answer more than what was already cited).

Assuming that the manacles already have an AC of 19 as an iron item (DMG ibid), how should the arcane lock make them more difficult to damage; by increasing their AC or hp, or both? What increase would be equivalent to a +10 increase to the DC of a strength check?

(1) The players have just started Rise of Tiamat but have not played Hoard of the Dragon Queen. I was using the adventure hook

wherein a captive dragon cultist is being escorted to the alliance council meeting but an ambush is made to attempt to free or kill her.

  • \$\begingroup\$ @NautArch The title is an abbreviated version of the bolded, as titles are. "How much should arcane lock protect" (with should being understood as providing an equivalent amount of protection from hp damage as the spell already describes for skill checks). It is opinion-based; I consider it good subjective by asking for answers based on mathematical equivalence - bounding the range of possible answers and defining how they should be defended, it is not entirely opinion-based. \$\endgroup\$
    – Kirt
    May 26, 2021 at 20:00
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    \$\begingroup\$ I understand that you would like to assume that the manacles get additional support from arcane lock, but without rules for how to do this, you are just asking for ideas for how to make this work (literally you ask how should this work.) That's an opinion. You could ask if anyone has done this, how, and they can talk about how it worked out. Or you could ask for a review of your own developed house rule as alternatives. \$\endgroup\$
    – NotArch
    May 26, 2021 at 20:56
  • \$\begingroup\$ @NautArch Please consider this question which asks 'what is a reason for easy combat encounters'? The question does not specifically ask for answers that have been used as such in the experience of the answerer. The accepted answer does not state that the answerer has had any experience in using encounters for the purpose suggested. How is that question a permissible idea-generation vehicle in a way that mine is not? Could you explain the difference to me? \$\endgroup\$
    – Kirt
    May 26, 2021 at 22:29
  • \$\begingroup\$ OK, I see what you are driving at. Comment gone. \$\endgroup\$ May 27, 2021 at 0:07

1 Answer 1


The addition in numbers makes it go from hard to nearly impossible to break the manacles with a strength check. Likewise, it should make it be nearly impossible to break the manacles in a single attack from a competent foe.

So, a fighter who has 2 attacks using an action surge with 1d8 damage will find it hard to break the manacles quickly. With a strength score above 10 they stand some chance, as with a normal set of manacles.

+10 to DC makes the strength check nearly impossible, so the manacles should be tough enough to resist all efforts by a low level character to break them, but not by someone with specialist help.

A greatsword with a 3 strength fighter can do 2d6+3 damage twice. That gives a max damage of 30. The manacles as such should be set a bit above that. 35 HP is reasonable, making it impossible for a level 1 fighter to break it in one round with their base abilities.

  • \$\begingroup\$ You seem to be taken it for granted that Arcane Lock would make the manacles harder to break. Can you add some support for why you think that is correct (and maybe also some experience support for your idea for how to add durability if you are able to show that it's needed in the first place? \$\endgroup\$
    – NotArch
    May 26, 2021 at 19:48
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    \$\begingroup\$ @NautArch It is not taken as granted that the manacles are harder to break - it is taken as assumed by the question itself. \$\endgroup\$
    – Kirt
    May 26, 2021 at 20:02
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    \$\begingroup\$ @Kirt That issue aside, this answer is still unsupported. \$\endgroup\$
    – NotArch
    May 26, 2021 at 20:39
  • \$\begingroup\$ Yes, they asked for an idea about how to homebrew how many HP it would have, and I suggested a method. Homebrew is inherently unsupported. \$\endgroup\$
    – Nepene Nep
    May 26, 2021 at 21:24
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    \$\begingroup\$ We don't do "homebrew this for me". \$\endgroup\$
    – NotArch
    May 26, 2021 at 21:28

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