I recall years ago, when L! wanted to retool his Librarian character and concept, that we worked out a bunch of likely abilities that would come with the job.

What we originally discussed were:

1. He can survive in space, so he doesn't need to breathe and he's not
affected by heat, cold, or radiation.

2. He can move through space, so he can probably levitate himself, not to fly very fast but to get to those hard-to-reach shelves.

3. He can sense any collection of data or of books at a distance; the biger the collection the further the distance.

4. He can know the contents of a book by touching it. In this way he can
become an expert in most things very quickly, although the knowledge fades eventually.

5. He can temporarily transfer that knowlege to another person by touching them. While this is meant to be helpful, if he chooses to zap it in all at once it can completely overwhelm most people (or computers), effectively knocking them out or sending them away gibbering. It's L's main natural offensive ability, so he probably keeps a few books "stored" in his brain for this purpose. A villain can get awfully distracted to suddenly learn "the History of Plumbing"!

6. He can speak any language of any book in the Lunar Public Library.

7. He can move without a sound. Once a day he can hush all sound in his
area.

Eventually I think we went with 1, 3, 4, and 5 (or else I just forgot about 2, 6 and 7). And 1 is a function of his uniform rather than an innate trailed ability.

And while I was digging in my old e-mails for that I also found correspondence about the Moon Public Library tech:

1. There are all kinds of ways to get to the Library, through warp-gates, teleporters, a space-craft landing hangar, etc. If neccessary, the Galactibus will come and pick you up to get you there. The Librarian can use his technology to locate any missing books from his catalogue and recover them.

2. There are lots of automated defences on the Library. No unauthorised
teleporting, phase-shifting, time-travelling, or dimension-walking are
possible without setting off the alarms, and only the most powerful beings could manage to do these things even then. There are all kinds of force fields, defence drones etc. that will deploy to protect the Library if it is threatened.

3. There are data-gathering devices that the Librarian deploys to make copies of other libraries before they're destroyed, to add to the collection on the moon. Taking copies of these other libraries is an important part of the Librarian's job.

4. There are computer systems to keep track of all those books, scrolls,
data-subes, stone tablets, light-cubes etc. They're so advanced that they can operate through a seemingly old-fashioned card index. All the technology at the library is very advanced, but it's all disguised to look very old-fashioned.

5. The library is able to shift around where its bookcases are, so that
whatever works the public wants are always somewhere on a shelf in the main rotunda - for as long as they're needed! Of course there are private study rooms and a no-entry book stack that goes on for miles and levels where things are stored until needed.