What literary devices are used in Mercutio's quote in act 1 of Romeo and Juliet?

In Shakespeare's Romeo and Juliet, the Bard employs the dramatic character of the foil. A foil is a character set up as a contrast to another character. This contrast makes the particular qualities of each character stand out. The Nurse is a foil to Juliet and, likewise, Mercutio is a foil to Romeo. Both Romeo and Juliet are romantics who idealize love as spiritual and a mutual adoration between two people. In contrast, the Nurse and Mercutio are anti-romantic and emphasize the sexual and physical aspects of love.

In Act I, Scene 4, Romeo, Mercutio, Benvolio and the other Montague men are on their way to Capulet's party. It is known to Mercutio that Romeo has been spurned in his affection for Rosaline. Ever the skeptic and joker, Mercutio advises Romeo to have fun at the party and to dance. But Romeo is very serious over his recent lack of success with Rosaline. He contemplates the cruel aspects of love when he says,

Is love a tender thing? It is too rough,
Too rude, too boisterous, and it pricks like thorn.

If love be rough with you, be rough with love. Prick love for pricking, and you beat love down.

What literary device does Shakespeare use in these lines from "Romeo and Juliet", and what does it mean?

These lines use personification, or the giving of human qualities to inanimate objects or ideas. In these lines, Capulet finds Juliet and thinks she is dead, and he states that instead of marrying Paris (as Capulet had wanted), Juliet has married death, meaning that she has met with death and now will spend the rest of her life with him (as if death were her groom). Therefore, instead of having Paris as a son-in-law, Capulet has death as a son-in-law. Instead of having Paris as his heir, Capulet has death as his heir. Capulet likens Juliet's death to a marriage between Juliet and death. In addition, these lines use the literary device of anaphora, or the repetition of a word at the beginning of different clauses that follow each other (in this case, "Death" is repeated). Anaphora is used to emphasize words; in these lines, Capulet draws constant attention to the death of his daughter, Juliet.

The device is 'personification', which is a form of metaphor. What personification does is to give human qualities or attributes to something that isn't strictly a human. So here, the abstract noun 'death' is turned into a metaphorical person, capable of doing things: and given, you'll notice, a capital letter to denote a proper name.

'Death', then can perform human actions: he can be Capulet's son-in-law and heir, he can marry Juliet, and when Capulet dies (this is the end of your quote!) he will leave all his money to this Death. Is he being literal? No. He's pointing out despairingly that, instead of his daughter being married to Paris, as he had hoped, she has become married, metaphorically to Death: she has died.

Incidentally, to aid your understanding of this quote (and, actually, this play) it might be worth my pointing out that 'death' to the Elizabethans meant 'orgasm' as well as the noun from the verb 'to die'. So death and sex are always related in this play, which, if you think about it, gives a whole new spin to 'Romeo and Juliet''s odd combination of passion and love with violence and hate.

Hope it helps!

What literary devices are used in Lady Capulet's quote in "Romeo and Juliet"?

This multi-part response is neither correct nor incorrect. Instead, each part requires additional context or expansion.

1. Indeed, this passage contains hyperbole, which is a literary device expressing exaggeration. Although Lady Capulet states, “I would the fool were married to her grave!” she does not wish for Juliet (“the fool”) to be literally dead and in her grave. Nonetheless, Lady Capulet is so frustrated with and angry at Juliet’s refusal to marry Paris that she does not know what to do. At that moment, an absence or negation of Juliet’s existence would provide a solution to this vexing problem to Lady Capulet. This example of hyperbole emphasizes Lady Capulet’s strong emotions.
2. The statement “I would the fool were married to her grave!” shows irony—specifically dramatic irony. Dramatic irony is a situation where the audience or reader knows something that a character doesn’t. Therefore, Lady Capulet’s utterance demonstrates dramatic irony in that she has no idea that Juliet is already married to Romeo. Second, she does not know that Juliet will end up in a grave by the end of the play—in a drug-induced coma, then mourning the late Romeo, then killed by her own hand.
3. The AI-generated response of metaphor is correct, but the explanation is unclear and incorrect. The metaphor in the statement “fool were married to her grave” is not a connection between marriage and death but between “grave” and husband. The metaphor is the substitution of “grave” for an actual husband. In other words, Juliet’s husband is death. Her literal husband is Romeo, but she ultimately marries death by the end of the play by committing suicide.
4. This passage does include alliteration, but even more than what is noted in the AI-generated response. The AI-generated response notes that the repetition of the w sound in “would” and “were” is an example of alliteration to emphasize Lady Capulet’s frustration and anger. Another example of alliteration is the repetition of s in “AY, sir, but she will none, she gives you.” The repeated s and sh sounds recreate spitting and hissing noises, illustrating her disgust and anger.
5. Finally, the AI-generated response mentioned but did not separate out the literary device of foreshadowing from the literary device of irony. “I would the fool were married to her grave!” foreshadows Juliet’s death, unbeknownst to Lady Capulet or anyone at this point in the play.