Researching both spell formulae and magic item schema requires a library. Likewise, libraries are used to uncover lore (associated with the Arcana, History, Nature, and Religion Skills).
Though adventurers often pay coin in order to access the libraries of either institutions, sages, or others with access, those who establish themselves may wish to possess a library of their own. Likewise, adventurers may find or loot tomes or even portions of libraries that may contribute to an overall library.
Libraries are rated by their total value in gold pieces. As characters gain new tomes or portions of libraries, they simply add them all together to determine what degree of usefulness this overall library provides.
Libraries do not care for themselves. While an individual may tend to the organization, curation, and even repair of small collections, larger libraries require a minimum number of Skilled workers to see that they are kept in good condition and able to be referenced.
- Small (1000 gp): A small library is a few book shelves worth of space, or enough to fill a fair sized cabinet. Lore libraries can research up to DC 15 topics. Formula libraries can research up to 1st level spells, and schema libraries can research up to Common magic items.
- Modest (5000 gp): A modest is a small room's worth of books, amounting to five or so bookshelves. Lore libraries can research up to DC 20 topics. Formula libraries can research up to 3rd level spells, and schema libraries can research up to Uncommon magic items.
- Good (10,000 gp): A good library is a sizeable room's worth of materials, often filling groaning shelves and cabinets with books, scrolls, and folios. Lore libraries can research up to DC 25 topics. Formula libraries can research up to 5th level spells, and schema libraries can research up to Rare magic items. Requires at least 1 Skilled worker to maintain
- Impressive (50,000 gp): An impressive library fills multiple rooms, even quite large ones. They tend to be rather rare, and certainly live up to their name in terms of their breadth of lore. Lore libraries can research up to DC 30 topics. Formula libraries can research up to 7th level spells, and schema libraries can research up to Very Rare magic items. Requires at least 3 Skilled workers to maintain.
- Legendary (150,000+ gp): A library of this size fills massive wings of vast establishments like Candlekeep or the Vault of Sages. They tend to be institutions in their own right. Lore libraries can research up to DC 35 topics. Formula libraries can research up to 9th level spells, and schema libraries can research up to Legendary magic items.
Unique books, insightful folios, and other collections of writings may enlighten and contribute to the works of a library in and of themselves. Though such works are rare, they often provide an impressive boon to a library, in the form of bonus percentages towards accomplishing certain kinds of research.
A library's special collections details a topic, plus a percentage bonus to research done toward that specific topic. The value of such collections also adds to the overall value of a library, making them doubly worthwhile additions. Most individual works do not contribute any more than 5%, although multiple applicable special collections do stack for a given bout of research.
If a schema library owns both Secrets of the Emerald Circle Regalia (a tell-all tome on the magic items of a certain faction of druids granting +5% to researching natural magic items) and Ebelthur's Treatise on Staves (an overblown work that grants a 2% bonus to research on magical staves), researching a staff of the woodlands gains a +7% check overall.
Sometimes, a special collection simply adds value to more than one library type at a time. A tome that delves into fire magic may add its value to both a formula and a schema library in addition to providing a +3% to researching spells or items that wield fire, or a book on ancient elven magic might provide a +1% bonus to enchantment or illusion spell research as well as contributing its value to both an Arcana and History library.