Flattened by a cold, I can’t do justice to today’s intended topic, which was going to be the next part of the History of the Fighter. Instead, I’m reposting and touching up a piece from my personal blog, Harbinger of Doom. I’ve gone through the Player’s Handbook for every kind of reaction to work out its timing. Even two reactions with the same trigger don’t necessarily have the same timing, and the phrasing could stand to be clearer.
As a foundation to talk about timing, an action has more timing steps than we usually talk about, as follows. This won’t be exhaustive; there are too many possibilities for that. It’s generally applicable, though. In principle, a reaction could occur any time after Step 1 and before Step 14.
- The acting player declares an action, such as Attack.
- The acting player declares the target(s) of that action, if any.
- The acting player rolls dice if appropriate. (The next few steps are rearranged for effects with saving throws.)
- The acting player observes the result.
- The acting player applies appropriate modifiers.
- The acting player announces the result.
- The player of the target(s) parse the result (usually announcing “hit” or “miss”).
- The acting player rolls damage.
- The acting player observes the result.
- The acting player applies appropriate modifiers.
- The acting player announces the result.
- Someone (the DM, usually) narrates something now, depending on the table’s customs and how much of a hurry everyone is in.
- The player of the target(s) record the damage or conditions.
- Move on to the next action or person.
As you see, when you’re actually playing the game, you mentally collapse several of these steps into a single process, but for reaction declarations, it’s important to break things down as finely as possible. Not “important for human use” – humans are great at going back to something they just said and changing the consensual fiction’s outcome. But game designers like to play around with decisions made on incomplete information, so this stuff matters. In fairness, though, you can spindle, fold, and mutilate the precise implementation a mighty lot before it rises to the level of game-breaking.
Below, I’ve tried to categorize features, spells, and rules elements from the Player’s Handbook that use reactions according to their trigger, with explanations where the timing of those triggers is questionable. I haven’t tried to use the step numbers I create above, for fear that that would only make things more confusing or open the less fruitful kind of nitpicking debates.
Sage Advice has clarified some of these questionable points over the last two and a half years. For example, the DMG says that “when a reaction has no timing specified, the reaction occurs after its trigger finishes (DMG, 252). In contrast, an opportunity attack specifically takes place right before its trigger finishes…” That’s good default handling, though some ways of specifying timing are still murky.
When you take damage from a creature
- Retaliation (Path of the Berserker, 14th level) grants a melee attack. This probably happens after the triggering damage, and dropping the attacker doesn’t negate the damage. It’s less clear whether you can still make this attack if the triggering damage puts the berserker at 0 hit points.
- Parry (Battle Master maneuver) reduces damage. Despite the technical phrasing, which would suggest that the damage is already applied to the character, the obvious intent is that you use this reaction after the damage roll but before damage is applied.
- Misty Escape (Archfey Patron, 6th level) turns you invisible and teleports you up to 60 feet to a destination you can see. This does not seem to negate damage.
- Hellish rebuke (1st-level evocation) deals damage in response to a creature damaging you. Timing is straightforward.
When a creature makes an attack roll
- Cutting Words (College of Lore, 3rd level) modifies a roll by the result of another die roll in the step between the die stopping and the DM declaring the outcome. It hinges, then, on players not knowing the NPC’s attack bonus. It’s implied, but not made explicit, that the bard gets to know the die’s natural result. If you don’t get to know this, though, there was never any point to allowing you to wait until the die was cast.
- Combat Inspiration (College of Valor, 3rd level) increases the user’s AC by the result of another die roll, again in the step between the die stopping and the DM declaring the outcome. Here the text is more explicit about information: “after seeing the roll but before knowing whether it hits or misses.”
- War God’s Blessing (War Domain, 6th level) grants a +10 bonus to an attack roll, declared “after you see the roll, but before the DM declares whether the attack hits or misses.” Here, the main point of letting you see the roll is so you don’t try to boost a natural 1. Even a roll of a 2 should hit most targets, after a +10 bonus on top of other modifiers.
- Bend Luck (Wild Magic, 6th level) lets you spend 2 sorcery points to add or subtract 1d4 from the roll. You declare this “after the creature rolls but before any effects of the roll occur,” which is sort of murky rules language compared to the other features with the same trigger.
- Entropic Ward (Great Old One Patron, 6th level) lets you impose disadvantage on an attack roll, and thus needs to be declared before you have any information from the roll. There’s a further effect if the attack winds up missing, so it doesn’t feel like a waste if the attack was a miss even without disadvantage.
- Instinctive Charm (School of Enchantment, 6th level) lets you attempt to redirect an attack that a creature makes against you. You explicitly declare this feature before you know the outcome of the attack roll. This is similar to other redirecting effects, except that it’s not melee-only, and the attacker gets a saving throw.
- Illusory Self (School of Illusion, 10th level) lets you make an attack roll automatically miss. The timing of this declaration is not spelled out as clearly as other reactions, but I assume it has to be declared before you know anything about the attack result.
When a creature makes an ability check
- Cutting Words (College of Lore, 3rd level), as above. NPCs don’t make a whole ton of ability checks in combat; Athletics or Acrobatics checks in relation to shoving or grappling, Stealth, and Perception rolls are the bulk of the in-combat work of skills. The implication of contested checks as part of social scenes makes this an alluring option, but the player goes in without a lot of clear understanding of whether social encounters will rely on contested rolls or fixed DCs (both valid approaches within the rules, but with radically different interactions with this feature).
- Bend Luck (Wild Magic, 6th level), as above.
When a creature makes a damage roll
- Cutting Words (College of Lore, 3rd level), as above. The hidden information of a damage roll is much less significant than the hidden information of an attack roll or ability check. The possibility of fully negating a hit is a bigger deal than mitigating damage by a random amount, but since Cutting Words can’t modify saving throws (and basic Bardic Inspiration requires preparation), this is the only way for Cutting Words to do anything about damaging effects with saving throws.
When you are attacked
- Warding Flare (Light Domain, 1st level) imposes disadvantage on the attack roll. In principle, it should only be declared after the DM has announced the attack and before the DM has rolled. In practice, I assume that a lot of tables allow the player to declare this reaction after the DM has rolled, with or without the player knowing anything about the roll result. There’s no clear practical difference between “when a creature makes an attack roll” and “when you are attacked,” other than the reactor needing to be the target in the latter case.
When you or another creature takes damage
- Dampen Elements (Nature Domain, 6th level) grants resistance to a single instance of acid, cold, fire, lightning, or thunder damage. This obviously takes effect in the step between the damage roll and the damage getting applied to the character’s hit point total, though ultra-formal rules parsing might insist that that means retroactively precedes the damage roll or something – here I’m thinking of Magic: the Gathering’s stack rules, and how confusing the timing of some reactions (like Regenerate) got when M:tG was translated to electronic format. Fortunately, D&D has a human running it, but it poses interesting design questions, if and when someone tries a Temple of Elemental Evil-style, ultra-faithful 5e video game.
- Projected Ward (School of Abjuration, 6th level) lets the Abjurer extend their Arcane Ward to another creature within 30 feet, negating some or all of the incoming damage. (The Arcane Ward does the same for the Abjurer personally without spending a reaction, though it’s otherwise phrased similarly to a reaction trigger.) Keep this one in mind for combination with on-hit triggers that don’t pay attention to later damage totals.
When a creature hits you with an attack
- Wrath of the Storm (Tempest Domain, 1st level) deals damage when a creature hits you with an attack (sure, there’s a saving throw, that’s not important right now). This is therefore declared after the DM has announced the result of the attack roll, but before the damage roll and any reactions that occur downstream (for instance, the new Oath of the Redeemer’s Aura of the Guardian). Wrath of the Storm doesn’t require the cleric to suffer damage, it just requires them to get hit. I assume that even if the reaction reduces the attacker to 0 hit points, it does not then negate damage that the cleric suffers.
- Deflect Missiles (Monk, 3rd level) reduces damage from a ranged weapon attack. Deflect Missiles doesn’t require that a creature be the attacker – the monk can deflect trap projectiles too, as long as they’re resolved with ranged weapon attacks. The one weird thing here is not actually about reaction timing, but about carrier effects that trigger on a hit, such as poison – you can negate the damage, which in the fiction means you gracefully catch the missile, but still suffer effects that come from getting hit. You can’t use this to catch a ranged weapon attack that was a near miss… even though the fiction is about converting a hit to a near miss.
- Giant Killer (Hunter Archetype, 3rd level) lets you make an attack against a Large or larger creature within 5 feet that hits you. The text makes it clear that your attack goes off after its attack.
- Uncanny Dodge (Hunter Archetype, 15th level; Rogue, 5th level) lets you halve the damage of an attack. The notable thing about the timing here is that you declare this after the attack roll, but before the damage roll. With the vast range of possible NPC damage values, you’re operating on fairly little information here. I suspect, without a lot of evidence, that a lot of DMs aren’t sticklers about this declaration timing.
- Defensive Duelist (feat) lets you add your proficiency bonus to your AC against a single melee attack. You declare this after you know it’s a hit, so presumably you know the exact roll result and whether this reaction can successfully convert the hit to a miss. Since the amount of AC bonus is non-variable, this is a huge amount of information.
- Shield (1st-level abjuration) boosts your AC by 5 after you are hit. The text calls out that this bonus applies retroactively to the triggering attack, so you’re operating with maximum information; it also keeps applying until the start of your next turn. Shield is just straight-up amazing.
When a creature attacks a target
- Protection Fighting Style (Fighter, Paladin) imposes disadvantage on an attack roll, much like Warding Flare. But then I already said everything I need to say about this feature.
- Soul of Vengeance (Oath of Vengeance, 15th level) lets you make a melee attack when your Vow of Enmity target makes an attack. It’s possible to argue that this attack occurs between the declaration of the attack and the attack roll, and thus reducing the target to 0 hit points might prevent the attack roll from taking place. This timing and possible later effects are a bit unclear.
- Sentinel (feat) lets you make an attack when an enemy attacks one of your allies that does not also have the Sentinel feat. The timing is straightforward.
- Notably, Sentinel also modifies your opportunity attacks, and that change has more involved timing effects: the trigger for an opportunity attack is a creature leaving your reach, but a hit with Sentinel reduces the creature’s speed to 0, so it never leaves that starting space – in a sense, preventing the original trigger. Reading the opportunity attack rules makes it clear that this is the correct timing, however.
When you take the Attack action on your turn
- Commander’s Strike (Battle Master maneuver) opens the door to an ally spending a reaction on the Battle Master’s turn. There’s no fiddly timing here – it just costs a reaction.
When you hit a creature with a weapon attack
- Maneuvering Strike (Battle Master maneuver) again opens the door to an ally spending a reaction on the Battle Master’s turn. Movement from Maneuvering Strike does not provoke opportunity attacks, so there’s some avoidance of cascading reactions, but there are enough triggers floating around that it could still happen.
When a creature misses you with an attack
- Riposte (Battle Master maneuver) lets the Battle Master make an attack following a miss. Timing seems straightforward.
- Giant Killer (Hunter Archetype, 3rd level) works as above, but also triggers if that creature misses you.
- Stand Against the Tide (Hunter Archetype, 15th level) lets you force the attacker to repeat that attack against a new target other than itself. Timing seems straightforward.
When you fall
- Slow Fall (Monk, 4th level) reduces falling damage.
- Feather fall (1st-level transmutation) causes you or an ally to fall slowly enough to suffer no harm, as long as they’re not falling for longer than this spell’s 1-minute duration.
When a creature is hit by an attack
- Opportunist (Way of Shadow, 17th level) lets the monk make a melee attack against a target that has just gotten hit by anyone else.
When a creature casts a spell
- Spell Thief (Arcane Trickster, 17th level) lets you temporarily negate a spell’s effect against you (an AoE may still affect others) and steal knowledge of the spell, if the caster fails a special saving throw. The timing here is explicitly after the spell is cast and its targeting declared. Let me just say that this feature is one of few hard negations in the Player’s Handbook, and its once-per-long-rest limit is the only thing that makes it even faintly okay. Well, that the fact that Arcane Tricksters still only have one 4th-level spell slot, and nothing higher.
- Mage Slayer (feat) lets you make a melee weapon attack against the caster, if they are within 5 feet. Timing is straightforward.
- Counterspell (3rd-level abjuration) allows you to negate a spell as it is being cast. It’s not clear how much information you should receive about what spell your enemy is casting before declaring this reaction (since 5e doesn’t have Spellcraft checks, and Arcana doesn’t explicitly do that), but the timing is obvious.
- Shield (1st-level abjuration), as mentioned above, also negates magic missile for its duration, and is declared after magic missile’s caster declares you as the target of one or more missiles.
When a creature makes a saving throw
- Bend Luck (Wild Magic, 6th level), as above. This is one of the situations where you’re most likely to spend your reaction on your own turn, since you’re a spellcaster and all.
- Shield Master (feat) lets you turn a Dex save for which you would, on a success, take half damage into no damage. The phrasing here is just a tiny bit clunky: is the trigger being subjected to the effect, or is it succeeding the saving throw? In the former case, you might spend your reaction, fail the saving throw, and gain no benefit, because this feature doesn’t offer half damage on a failed save. This is one of a tiny number of places where the reaction trigger uses “If” rather than “When” or “Whenever.”
When another creature attempts to charm you
- Beguiling Defenses (Archfey Patron, 6th level) attempts to reflect charm effects back against their source. Another element within this feature makes you immune to that charm in the first place, so there’s no timing question unless a creature ignores charm immunity. (If you ever went heads-up against your Patron, I strongly support letting that Patron ignore immunities that they gave you.)
When a creature provokes an opportunity attack
- War Caster (feat) lets you cast a spell in place of your opportunity attack, so like the second feature of Sentinel it is just modifying the most core of all reactions.
- Ready (the action) lets you create your own trigger, based on any perceivable circumstance. Since you can slice that awfully thin, it’s possible to create some timing issues. In principle, you can set the trigger to “when the creature starts to cast a spell” or “when the creature starts to make an attack,” thus pre-empting the action. This is more of a problem for reactions like “if a creature approaches to within its reach + 5 feet of me, I will move away from it” – if you can run it out of movement speed while you’re still outside of its reach, then you’re set, and the trigger was such that you were never leaving its reach.
If your mount is knocked prone
- Mounting and Dismounting allows you to gracefully dismount and land on your feet, if you have a reaction to spend. The rules just trust you to know that this wouldn’t work if your mount is flying.
I haven’t gone through the Dungeon Master’s Guide, which doesn’t have many reactions outside of, possibly, some magic items, or any other books or UA content. If you find this tabulation especially useful, let me know and I’ll consider doing that legwork as well.
The heavy use of reactions created some problems in 4e combat, but it also made each player’s off-turn an interesting part of the game and gave players much-needed incentive to pay attention when it wasn’t their turn. 5e has trimmed a lot of the mental load out of reactions, usually keeping them quick to resolve. If you’re working in 5e’s design space, you’ll need a subtle understanding of reactions and timing – I hope this post helps!