Library & files
ID3 tags
ID3 tags are the metadata written inside an audio file — title, artist, album, genre, year, comment, and on DJ files often BPM and key. They travel with the file rather than with the software that read it.
Measured in our catalog
Our catalog carries a tempo on 443,307 tracks and a key on 443,414 of 443,460 — and an ISRC, the one identifier built to survive a re-release, on zero.
Label sits on 443,273 rows and a release date on all 443,460, because those are what a store supplies. Tempo and key are not supplied by anyone — they are analysed, which is exactly why they are the two fields missing from most purchased files. The empty ISRC column is the honest half of the picture: the tag that would make duplicate detection trivial is the one nobody fills in, us included.
443,307
Tracks with a tempo
443,414
Tracks with a key
443,273
Tracks with a label
0
Tracks with an ISRC
| Field | Tracks carrying it | Where it comes from |
|---|---|---|
| Release date | 443,460 | The store |
| Genre | 443,458 | The store |
| Key | 443,414 | Our analysis |
| Duration | 443,414 | The file |
| Label | 443,273 | The store |
| BPM | 443,307 | Our analysis |
| ISRC | 0 | Nobody |
Measured on 11 August 2026 across public tracks, counting a field as present when it is non-null and non-empty.
Why it matters
Tags are the only part of your preparation that survives leaving your own machine. A track dragged onto a friend’s USB arrives with whatever is written inside it and nothing else, so a library that lives in your software’s database and not in the files is a library you cannot lend.
They are also where the two most useful fields are usually missing, which is the whole argument for analysing a collection rather than trusting it.
Frequently asked
What ID3 tags matter for DJing?+
Title, artist, BPM, key and the comment field. The first two identify the record, the middle two decide what it mixes with, and the comment is the only free-text field that travels with the file.
Do BPM and key get written into the file?+
They can be, and it is worth doing. Left only in your software’s database, they vanish the moment the file is copied to another machine — which is precisely when you need them.
What is an ISRC code?+
A unique code identifying a recording across every store and release. It would make duplicate detection trivial, which is why it is worth noting that we hold one on none of our public tracks.
Related terms
Comment field
The comment field is free text inside an audio file, and the only metadata slot nobody else is using. DJs fill it with the things no other field holds — energy ratings, where a record works, what it mixes into.
Tag
A tag is a label you attach to a track so you can find it by something other than its name — a genre, a mood, a situation. A track can carry as many as you like.
Duplicate detection
Duplicate detection finds the same record stored more than once — usually by comparing artist and title after normalising punctuation and case, sometimes by duration or by an identifier inside the file.
Library database
Your DJ software keeps its own database of everything it knows about your collection — file locations, beatgrids, cue points, crates, play history. The audio files sit elsewhere on disk; the database is what turns them into a library.