SOURCE: Player’s Handbook

Ritual Caster’s Deceptively Simple Benefits

Benefit #1 – 

Two 1st level rituals from a class of your choice 

Simple enough, right? You get a book with two rituals, and you can cast those as rituals using the standard ritual casting rules while holding the book. They must be 1st level spells, but there are lots of good rituals.

Benefit #2 – 

Ability to add more rituals for the class you chose such as those in scrolls or a wizard’s spellbook

This feature lets you spend a bit of time and gold (2 hours and 50 gp per level of the spell) to gain more rituals and more powerful rituals.

Mechanics and Requirements

How to Ritual Cast

Ritual casting is not available by default to spellcasters: a feature must explicitly give it to them. You gain ritual casting only for the spells in your special ritual book, and can only use the book to cast those spells as rituals.

To ritual cast, you add ten minutes to the spell’s casting time, and you neither require nor expend a spell slot, then once you finish casting, the spell takes effect as normal. It’s unclear if you can ritual cast while walking around or even riding a horse: nothing in the PHB says you can’t, but it’s safe to assume rituals require some degree of precision, so talk to your DM ab

Key Stats

The only necessary ability scores are a 13 in either intelligence or wisdom: you want a decent wisdom on any character, but a 13 may be too high for some. Remember that even if you pick a charisma class, you don’t need a 13 charisma, just either intelligence or wisdom as per the requisite; Jeremy Crawford has confirmed this in a sage advice.

It may be tempting to increase the spellcasting ability for the ritual casting class you picked, but this is a mistake: none of these spells require or meaningfully benefit from your spellcasting ability modifier, although there may be a rare exception I’m unaware of.

Solid Ritual Caster Users

Top Classes

Barbarian – Putting magic on a nonmagical character always brings a new level of fun and utility, but barbarians, a stereotypically dumb class, are especially funny as spellcasters.

Rogue – Rogues want advantage because it guarantees their sneak attack and increases their chance to hit with their one or two big attacks a round. Rogues also need something to take hits for them due to their slightly underwhelming defense. Thankfully, Ritual Caster lets the rogue summon a familiar with Find Familiar, and then that familiar can provide advantage with the help action and act as a one-use meat shield. The only issue is the small costly component for Find Familiar.

Wizard – Wizards like spells and want as many as possible, especially the bookish scribes wizards. Despite being excellent utility casters already, Ritual Caster lets them double down by stealing rituals from Druid or Cleric, filling the ritual role of several classes at once.

Multiclassing Considerations

Multiclassing doesn’t really interact with Ritual Caster much. Rogues don’t benefit as much from the Find Familiar help action if they multiclass out of rogue and forfeit some future sneak attack dice, but that’s about it.

Racial Spellcasting Pitfalls

If you take Ritual Caster on a race with spells, try to make sure you’re not doubling down on the same spells. For example, Firbolgs can cast Detect Magic and have an innate one way communication with animals, so there’s less of a need to go Ritual Caster: Druid for these spells.

Combos, Tactics, and Synergies

Complementary Feats

Inspiring Leader can give temporary hit points to a Find Familiar, possibly allowing it to survive a weak source of damage instead of dying instantly. I don’t recommend taking it yourself for this purpose, but your familiar can benefit from it if you or someone else happens to have it already. 

Spells to Pick

Detect Magic helps locate magical hazards, odd spells, and magic items, so take it if nobody else can cast it. Find Familiar is absurdly strong and is my first pick for Ritual Caster. Ceremony lets you give one time bonuses to party members before the final fight, but talk to your DM: some may find this to be a bit cheesy.

If you can hunt down higher level rituals, and the gold and time costs are reasonable for you, it is absolutely worthwhile to copy them into your ritual book.

Phantom Steed is good due to the ludicrous speed: it’s immensely useful for anyone, but remember, even though the horse doesn’t instantly vanish as soon as it takes damage, it can still die instantly if it does. Leomund’s Tiny Hut is an invincibility field that guarantees a safe short or long rest, as long as you have the time to set it up. Water Breathing will let your whole party explore underwater. Rary’s Telepathic Bond is extremely useful for silent communication between party members, whether for stealth or social purposes.

Maximizing Ritual Caster Effectiveness

Find Familiar is my go-to pick, even if someone else in the party has a familiar already. Otherwise, be sure to pick spells that overlap as little with your existing abilities and your other party members as possible.

Remember that rogues, particularly phantom rogues using the Steady Aim feature in particular can benefit a lot from a Phantom Steed: here’s a video explaining how. The damage and mobility will be fantastic.

Final Thoughts on Ritual Caster

Ritual Caster is a good feat, but I rarely see it discussed; ritual spells are dependable, useful, and somewhat fun, but they’re not overwhelmingly stunning like War Caster’s concentration boost or Crossbow Expert’s bonus action attack. I recommend paying more attention to Ritual Caster whenever you’re picking feats.