When you are wielding a finesse weapon with which you are proficient and another creature hits you with a melee attack, you can use your reaction to add your proficiency bonus to your AC for that attack, potentially causing the attack to miss you.
{
"name": "Defensive Duelist",
"page": 165,
"__prop": "feat",
"source": "PHB",
"entries": [
"When you are wielding a finesse weapon with which you are proficient and another creature hits you with a melee attack, you can use your reaction to add your proficiency bonus to your AC for that attack, potentially causing the attack to miss you."
],
"reprintedAs": [
"Defensive Duelist|XPHB"
],
"prerequisite": [
{
"ability": [
{
"dex": 13
}
]
}
]
}