Databases. They make finding information as easy as typing a query. Some works extend this capability to finding information on the supernatural elements of the setting. You want information on known werewolves, undead, or wizards, this is where you go.
Despite the title referring to electronic databases, Tropes Are Flexible and this can easily take the form of a paper encyclopedia or the equivalent. It might even be a person or other sapient entity.
See also Monster Compendium, which applies to videogames but generally won't tell you about something until you've encountered it firsthand. Compare Tomes of Prophecy and Fate, which can be a book on every event past and to happen. Contrast Akashic Records, which is where the compendium itself is supernatural in origin but contains records of the mundane as well as the supernatural
Not to be confused with the Omniscient Database, which is when the database only holds mundane information but is improbably detailed or wide ranging.
- One of these becomes a plot point in an episode of GeGeGe no Kitaro (80s version) when it turns out the encyclopedia of yokai some kids have doesn't contain the Monster of the Week and it goes on a rampage in revenge for being left out.
- Yue's artifact in Mahou Sensei Negima!. It uncovers most of the information needed by the user.
- A Certain Magical Index has the eponymous Index Librorium Prohibitorium, a little girl who happens to have thousands upon thousands of magical books stored within her mind. As such, the power she holds within her is equally dangerous.
- Discworld series
- Death's library in sometimes functions like a Magical Database, instantly delivering books on very obscure subjects when he requests them, or writing out fresh text if his query doesn't require a long answer (the "some of the sheep" response from The Last Continent).
- Hex does this as well since he is basically a sentient, magical computer. As long as he has his teddy bear he'll find out what you want to know.
- In Gone in a Flash by Ryk E. Spoor, Jason Wood is told that he can't find out stuff about vampires from a nice cross-indexed database somewhere, so he sets out to create one himself.
- John Winchester's journal in the earlier seasons of Supernatural. Later seasons have Bobby fill this role. Or just the internet.
- Angel and Buffy the Vampire Slayer had Demons, Demons, Demons, your one-stop demon database.
- Grimm has the journals passed down in the Grimm family. They include detailed illustrations so future generations of Grimms can identify monsters they encounter and what their weak spots are.
- The Book of Shadows in Charmed is a magical tome the girls inherited which conveniently has listings for whatever monster they might be fighting that week, along with the appropriate counterspells to use. In one episode, after fighting a monster with no article, they add it to the book themselves.
- Warhammer 40,000 has the Black Library (not to be confused with the identically named Expanded Universe publication), a library that stores the information of just about everything involving the supernatural and daemonic, guarded by the Harlequins of the Laughing God, thus making it inaccessible to most of them.
- The Infinity Circuit of an Eldar craftworld. In addition to being a repository for the souls of their dead, Eldar can use the circuit to ask questions and seek wisdom, and even send messages to each other. It's basically a giant computer network, except you access it with Psychic Powers and it's powered by the souls of the departed instead of electricity, so this example gets bonus points for taking the "Magical" part of the trope name and making it literal.
- In Gabriel Knight 3, Gabriel's assistant Grace creates SIDNEY (Schattenjäger Information Database), a computer database of all information relevant to the cases that he might take on as an Occult Detective Schattenjäger. It in turn is based on the library of actual books that the line of Schattenjägers used to maintain in their family castle for the same purpose.
- CABAL, the Magitek supercomputer operated by the Inquisition in Exterminatus Now is supposed to be this. The protagonists mostly use it to store porn and pirated mp3s, of course...
- Leif & Thorn apparently has a lot of them, including translation dictionaries, which can be queried from a distance using their magical Internet.
- The SCP Foundation is a The Men in Black-esque organization that keeps a database of all their supernatural and preternatural objects, and technically the wiki itself is that database.
- On Soulless Ones from Angel of Death is a tome that, among other things, contains information on every lich and every magical power any lich possesses.
- Another book called On the Underworld has been mentioned, though we do not know how similar it is.
- The Junior Woodchuck's Guide from Disney's DuckTales (1987). It has a chapter on defeating dragons, for crying out loud.
- The Journals from "Gravity Falls", which contain information on such things as how to defeat gnomes among others.
- The character Skips in "Regular Show" is often relied on for explanations of supernatural occurrences.