How the editor works, step by step

This page walks through one edit from start to finish, then explains what actually lands in the file. If you'd rather just try it, the editor is on the front page and there's a 15-second practice file to play with.

What an MP3 tag is

An MP3 is mostly audio frames, one after another. Right at the front there's a small block of text and, optionally, a picture. That block is the ID3 tag, and it's the only thing a player looks at when it shows you a title, an artist and a cover. The audio doesn't know or care what it's called.

There are two flavours you'll meet. ID3v2 sits at the front of the file, holds as much text as you like in any language, and can carry an image. ID3v1 is the 1990s version: exactly 128 bytes at the very end of the file, 30 characters per field, no picture. Some old car stereos and cheap portable players only read that one, which is why the editor can write both. The what's inside guide shows both in hex if you're curious.

One edit, start to finish

1. Load the file. Drag an MP3 onto the dashed box, or click Choose a file. On a phone, the chooser opens your Files app.
2. Read what's there. The tag is parsed on your device and the form fills in. If the file has no tag at all, the fields stay empty and the status line says so. Either way, nothing has been sent anywhere.
3. Fix the fields. Title, Artist, Album, Year, Track number, Genre, Comment. Track numbers can be 3 or 3/12. Genre is a dropdown of the standard list, because that's the only form a genre can take in an ID3v1 tag.
4. Sort out the cover. Upload cover art takes a JPG or PNG. Square images look right everywhere; 600 to 1000 pixels is plenty. Remove clears whatever was there.
5. Decide about ID3v1. Leave the box ticked unless you know your player prefers a file without one. It costs 128 bytes.
6. Save. Click Save tags and download. Your browser writes a new file called yourname-tagged.mp3 into your downloads. The original is never touched, so there's nothing to undo.

What gets written

The editor writes an ID3v2.3 tag, which is the version nearly every tagger writes by default and the one Windows, macOS, phones and car stereos agree on. Text goes in as UTF-16, so a Hindi or Japanese title comes out the other side intact. The frames, for anyone who reads tag dumps:

If the ID3v1 box is ticked, a 128-byte block goes on the end too, with the same fields cut to 30 characters (28 for the comment), the track number as a single byte, and the genre as a code from the standard list. ID3v1 has no room for non-ASCII characters, so accents and non-Latin scripts are dropped from that copy only. The ID3v2 tag keeps them.

When a player ignores the change

You saved, you opened the new file, and the player still shows the old title or the old cover. Nine times out of ten the tag is fine and the player is showing you its cache. Music apps index a file once and then trust their own database. Remove the track from the library and add the new file, or clear the app's cache. Windows Explorer keeps its own thumbnail cache for covers, which is a separate annoyance with its own fix; the cover art guide goes through each one.

The tenth time, the player only reads ID3v1. Old car head units are the usual suspects. Make sure the box was ticked, and remember the 30-character limit: a long title will look cut off there and nowhere else.

Other things people ask

Why this page exists

Every library picks up a few tracks called Unknown artist, or a cover that belongs to a different album. I wanted a way to fix one file from any device without installing anything and without handing the file to someone's upload server. This is that, and this page is the manual.