Librarians trade books and related items. Their job site block is the Lectern.
Best trades
Enchanted books at every level, including treasure enchantments like Mending that the enchanting table cannot produce
24 paper for 1 emerald - a sugar cane farm feeds this trade all game
Bookshelf for 9 emeralds saves you the leather cost when building a level 30 enchanting setup
Full trade table
Novice
Villager wants
You get
In stock
Chance offered
24 x Paper
Emerald
16
67% JE / 100% BE
9 x Emerald
Bookshelf
12
67% JE / 50% BE
5-64 x Emerald + Book
Enchanted Book (random)
12
67% JE / 50% BE
Apprentice
Villager wants
You get
In stock
Chance offered
4 x Book
Emerald
12
67% JE / 100% BE
Emerald
Lantern
12
67% JE / 50% BE
5-64 x Emerald + Book
Enchanted Book (random)
12
67% JE / 50% BE
Journeyman
Villager wants
You get
In stock
Chance offered
5 x Ink Sac
Emerald
12
67% JE / 100% BE
Emerald
4 x Glass
12
67% JE / 50% BE
5-64 x Emerald + Book
Enchanted Book (random)
12
67% JE / 50% BE
Expert
Villager wants
You get
In stock
Chance offered
2 x Book and Quill
Emerald
12
50% JE / 100% BE
4 x Emerald
Compass
12
50% JE / 33% BE
5 x Emerald
Clock
12
50% JE / 33% BE
5-64 x Emerald + Book
Enchanted Book (random)
12
50% JE / 33% BE
Master
Villager wants
You get
In stock
Chance offered
3 x Emerald
Red Candle
12
100% JE / 75% BE
3 x Emerald
Yellow Candle
12
100% JE / 25% BE
Notes
Enchanted book price is 5-64 emeralds plus 1 book. The enchantment is random among all types, treasure included; better enchantments cost more. Break and replace the lectern before trading to reroll the offered book.
Once you trade with a librarian, its trades lock forever - reroll before the first trade.