How Reactions Work in D&D 5e (And the Best Ones to Take)

26 March 2026

Combat isn’t just a carousel of turns, it’s a chain of interruptions. A reaction is your once-per-round permission slip to act when a trigger you care about happens, even if it’s not your Initiative number. New players hoard attention for their turn and leak value everywhere else; veterans quietly farm reactions because shield, counterspell, and opportunity attacks all live in that pocket.

The one-sentence rule

You can take one reaction per round, and you regain your reaction at the start of your turn.

If you Ready an action, firing it usually uses that same reaction, don’t double-book yourself. Details: Ready.

Everyone’s default: opportunity attack

When a hostile creature you can see moves out of your reach, you can use your reaction to make one melee attack unless something prevents it (Disengage, teleport, being moved without using the creature’s movement, and so on).

That’s why doorway fighters feel strong, their reach draws a line on the map.

Full tour: opportunity attacks.

Reactions worth knowing (quick class sampler)

shield (Wizard / Sorcerer)

Trigger: you are hit by an attack or targeted by magic missile.
Effect: +5 AC until the start of your next turn, often turning a hit into a miss for that attack. Costs a 1st-level slot.

hellish rebuke (Warlock, among others)

Trigger: you are damaged by a creature within 60 feet that you can see.
Effect: fire damage (2d10 at base level) with a Dexterity save for half, see the spell’s text for slot scaling.

counterspell (Wizard / Sorcerer / Warlock / Bard)

Trigger: you see a creature within 60 feet casting a spell.
Effect: attempt to interrupt the cast. If the spell is 3rd level or lower, counterspell cast at 3rd level automatically ends it; for higher-level spells, roll an ability check using your spellcasting ability with DC = 10 + the spell’s level. Costs a 3rd-level slot minimum (counterspell itself is 3rd-level).

Full timing and table etiquette: Counterspell in 5e.

Uncanny Dodge (Rogue, 5th level)

Trigger: you can see the attacker and you are hit.
Effect: halve the attack’s damage, no resource cost, enormous survivability.

Deflect Missiles (Monk, 3rd level)

Trigger: you are hit by a ranged weapon attack.
Effect: reduce damage by 1d10 + Dexterity modifier + monk level; if reduced to 0, you may catch and throw for ki (per feature).

Parry (Battle Master maneuver)

Trigger: you are damaged by a weapon attack you can see; spend one superiority die.
Effect: reduce damage by die result + Dexterity modifier.

Protection fighting style (Fighter / Paladin, with shield)

Trigger: a creature you can see attacks a non-you target within 5 feet of you.
Effect: impose disadvantage on that attack roll. Requires a shield.

Sentinel (feat)

Adds precision to opportunity-control: read the feat text carefully, one clause can freeze an enemy that tries to leave after you hit with an opportunity attack; another can let you attack when foes near you strike your allies.

Ready isn’t “extra turns”, it’s “prepaid reaction”

You spend an action up front to maybe react later. Powerful for ambushes and door lines, but it competes with shield, counterspell, and opportunity attacks for the same one reaction.

Table habits that stop forgot-reaction syndrome

• After each enemy turn, ask once: did a trigger I own fire?
• If you’re the Counterspell player, say so once per tier so the table doesn’t double-spend interruptions.
• Don’t burn shield on theoretical danger, save reactions for the hits that actually threaten a down.

Loop back to the full combat frame anytime: how D&D combat works.