AMPLibraryAgent on Mac: what it is and why it uses CPU

What AMPLibraryAgent does

When Apple split iTunes into Music, TV and Podcasts in macOS Catalina, the library work that used to live inside iTunes moved into a shared background agent: AMPLibraryAgent. It owns the library database for those apps. When you add songs, it scans the files, reads tags, pulls artwork, and writes entries. When Sync Library (iCloud Music Library) is on, it compares your library with Apple's copy, uploads what is missing, matches what it can, and downloads changes made on your iPhone. When Music or macOS updates, it often has to migrate or rebuild the database to the new format.

It runs as you, starts at login, and keeps going whether or not the Music window is open. That last part is what surprises people: you quit Music, the fans keep spinning, and Activity Monitor shows a name you have never heard of at the top of the list.

What normal looks like

Why AMPLibraryAgent is using CPU right now

1. A big import just happened. Dragging a folder of music into Music, or adding a ripped CD collection, gives the agent thousands of files to scan and tag. This is the most common cause and it ends when the import does.
2. Sync Library was turned on, or you signed into a new Apple ID. The first sync compares your whole library with iCloud, track by track. On a large library this is the longest job the agent ever does.
3. Music, TV or macOS was just updated. Library database upgrades run in the background after an update. Reports of AMPLibraryAgent at full CPU cluster around major releases, with Catalina being the first and loudest.
4. Artwork or metadata refresh. Music periodically refreshes artwork and catalog data for matched tracks. Smaller than an import, but visible.
5. A damaged library file. If the agent hits a corrupt entry it can retry endlessly. The giveaway is high CPU with no change in the library for hours and no import in progress.
6. An external drive with the library went away. If your Music library lives on a drive that was unplugged or went to sleep, the agent can spin waiting for it.

Is it safe to quit AMPLibraryAgent?

Quitting it is harmless but rarely useful. It is a login agent, so launchd restarts it, and when it restarts it resumes the same job from where the database says it left off. Force quitting during a library write is the one thing worth avoiding, because interrupting a database migration is how libraries end up damaged. The safe version of the same idea is to quit Music (and TV and Podcasts), give the agent a minute to finish writing, and then restart the Mac. That resets the agent cleanly and resumes any unfinished sync on the next launch.

Its siblings have similar names: AMPDeviceDiscoveryAgent (finds iPhones and iPads for syncing), AMPArtworkAgent (artwork), AMPDevicesAgent (device sync). Type any of them above.

What to do, in order

1. Check whether a job is actually running

   Open Music. Look at the bottom of the sidebar or the activity indicator in the window for an import, match or upload in progress. If the song count is rising, it is working. Leave it, ideally on power.

2. Give it an hour, overnight for a large library

   A library of tens of thousands of tracks on a slow connection genuinely takes hours to sync the first time. The agent is single-minded; it finishes faster if you do not keep restarting it.

3. Reconnect the library drive

   If your library lives on an external disk, plug it in and wake it. The agent stops spinning as soon as the files are reachable.

4. Quit Music, TV and Podcasts, then restart

   Quit the three apps so the agent has nothing to serve, wait a minute, and restart the Mac. On login the agent starts fresh and continues any unfinished sync from the database, not from scratch.

5. Turn Sync Library off and on

   Music, Settings, General, Sync Library. Switch it off, wait a few minutes, switch it back on. This restarts the cloud comparison cleanly. Downloaded tracks stay on the Mac; purchased and matched items come back when sync resumes.

6. Hold Option while opening Music to pick or rebuild the library

   If the agent stays at full CPU for days with no change, the library file may be damaged. Holding Option as Music opens lets you create a new library or choose a different one. Keep the old library folder; nothing is deleted. Re-add your music folder and let the agent rebuild once, properly.

When to worry

Worry when the agent has been at full CPU for more than a day, the song count in Music has not moved, no import is showing, and a restart brings it straight back. That is a damaged library or a missing drive, and the rebuild in step six is the fix. Do not worry about hours of activity after a big import or a first sync; that is the job you asked for. Do not worry about it running with Music closed; it is a background agent and that is normal. And do not install a cleaner to deal with it; nothing a cleaner does touches the Music database, and some of them break it.

Safe to Quit, the Mac app this site comes from, marks AMPLibraryAgent as one to let settle and tells you it stops on its own, which is the whole answer most of the time.