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

26 March 2026

Reactions are one of the most underused parts of D&D combat — especially by new players. You get one per round, they can be used on anyone’s turn (not just yours), and some of the best abilities in the game are reactions.

What is a reaction?

A reaction is a special action you take in response to a trigger. That trigger can happen on your turn, on an ally’s turn, or on an enemy’s turn.

You have 1 reaction per round. It resets at the start of your turn (not the start of the round).

If you use your reaction, you don’t get another one until your next turn begins.

The most common reaction: Opportunity Attacks

When an enemy leaves your melee reach without Disengaging, you can use your reaction to make one melee attack against them. This is the reaction every character in the game has by default.

Key details:

• Triggers when a hostile creature leaves your reach
• You can only make one melee weapon attack (not a full attack action)
• The enemy must move out of your reach — teleporting or being moved by an external force doesn’t trigger it
• The Disengage action lets a creature leave without triggering opportunity attacks

This is why creatures that want to run away from melee fighters usually Disengage first.

Class reactions to know

Shield (Wizard, Sorcerer)

Trigger: you are hit by an attack or targeted by Magic Missile. +5 AC until the start of your next turn, and if that makes the attack miss, it misses.

This is arguably the best defensive reaction in the game. At levels 1–5, when enemies hit for single attacks, this can negate damage entirely. It costs a 1st-level spell slot.

Hellish Rebuke (Warlock)

Trigger: you take damage. Deal 2d10 fire damage (Dexterity saving throw for half) to the creature that hurt you. Costs a spell slot.

The Warlock’s reaction option — punishes enemies for attacking you. Since Warlocks have limited spell slots, use it when a hit actually hurt.

Counterspell (Wizard, Sorcerer, Warlock, Bard — 3rd level)

Trigger: a creature within 60 feet casts a spell. Interrupt and cancel the spell. Automatically succeeds against 3rd-level spells or lower. For higher-level spells, make an ability check.

This is the most powerful combat reaction in the game in the right circumstances. A well-timed Counterspell can prevent a fight-ending spell. The trade-off: it costs a spell slot and you’re competing for your reaction.

Uncanny Dodge (Rogue — level 5)

Trigger: an attacker you can see hits you. Halve the damage of that attack.

No resource cost. Halving damage from any hit you can see coming is consistently strong for a Rogue who is often targeted.

Parry (Fighter — Battle Master Manoeuvre)

Trigger: you’re hit. Spend a superiority die to reduce damage by the die result + Dexterity modifier.

Battle Master Fighters who invest in survival use this. Works well stacked with other defences.

Deflect Missiles (Monk — level 3)

Trigger: hit by a ranged weapon attack. Reduce damage by 1d10 + Dexterity modifier + Monk level. If damage is reduced to 0, you can throw it back at the attacker (costs ki).

Monks become significantly harder to hit from range once this comes online.

Protection Fighting Style (Fighter, Paladin)

Trigger: a creature attacks a target adjacent to you. Impose disadvantage on that attack roll. Requires a shield.

Protector builds use this to guard fragile allies. Useful but situational — you need to be adjacent to both the attacker and target.

Sentinel (Feat)

The Sentinel feat gives two extra reaction options:

1. When you hit with an opportunity attack, the creature’s speed becomes 0 for the rest of the turn (they stop cold).
2. When a creature within your reach attacks a creature other than you, you can make a melee attack against them as a reaction.

This is one of the strongest feats for Fighters and Paladins who want to control space and protect allies.

The Ready action and reactions

If you take the Ready action on your turn, you set a trigger and an action to take when it fires. When the trigger occurs, you use your reaction to execute that readied action.

You can Ready almost any action — a spell, an attack, a dash. But:

• Readied spells consume concentration when you hold them
• You still use your reaction when it fires
• If the trigger doesn’t happen, your readied action does nothing (but you still used your action setting it up)

Practical tips

Don’t forget your reaction. New players often remember their action and bonus action and forget reactions exist. After each enemy turn, ask yourself: “Did that trigger anything I can react to?”

Save it for the right moment. Your reaction is precious if you have options like Counterspell or Shield. Spending it on an opportunity attack might be worse than holding it for an incoming enemy spell.

Communicate with your party. If you have Counterspell, tell your party. They may hold their action so you can react to the right moment.

Sentinel + Polearm Master is a famous combo. Polearm Master gives an opportunity attack when an enemy enters your reach (instead of just leaving it). Sentinel stops them cold when you hit. Together, they lock enemies down completely. Ask your DM before committing to it — some find it extremely powerful.