tone is a cross platform audio tagger and metadata editor to dump and modify metadata for a wide variety of formats, including mp3, m4b, flac and more. It has no dependencies and can be downloaded as single binary for Windows, macOS, Linux and other common platforms.

The code is written in pure C# and utilizes the awesome atldotnet library to provide full support for a wide variety of audio and metadata formats.


The main purpose of tone is to tag m4b audio books for myself. It is planned as a successor to [m4b-tool].

  • dump metadata of audio files
    • different metadata formats (e.g. chptfmtnative, ffmetadata, etc.)
    • file information (bitrate, channels, duration, etc.)
    • support for filterable json output (similar to jq)
    • extensive list of supported tags (default fields like album or *artist as well as custom fields, covers, chapters, etc.)
  • tag audio files with different kinds of metadata
    • different file formats (e.g. mp3, m4b, and flac)
    • extensive list of supported tags (default fields like album or *artist as well as custom fields, covers, chapters, etc.)
    • filename to tags via --path-pattern (see below)
    • custom javascript taggers via --script and --script-tagger-parameter

Future plans

  • split large audio files into multiple smaller files (e.g. by chapters) using ffmpeg, fdkaac and CliWrap
  • merge multiple smaller audio files into large ones auto generating chapters using silence detection with ffmpeg, fdkaac and CliWrap
  • write unit tests and more detailed documentation

Support me via GitHub sponsors

If you are using any of my projects and find them helpful, please consider donating to support me. I plan to use the money to support other open source projects or charitable purposes. Thank you!

sponsor me and donate


dump tags

# show help
tone dump --help

# show all tags for single file (input.mp3)
tone dump input.mp3

# show title and artiest tag recursively for all files in directory with extension m4b in FFMETADATA format
tone dump audio-directory/ --include-extension m4b --format ffmetadata --include-property title --include-property artist

# show album only via json format and JSONPath query
tone dump "input.mp3" --format json --query "$.meta.album"

# show audio stream information via JSONPath query
tone dump "input.mp3" --format json --query "$.audio"

modify tags

# show help
tone tag --help

# change title tag
tone tag input.mp3 --meta-title "a title"

# change a custom field, auto-import covers nearby and show debug info on error (--dry-run simulation)
tone tag --debug --auto-import=covers --meta-additional-field "©st3=testing" input.m4b --dry-run

# recursively set tags genre, artist, series, part and title by path pattern (--dry-run simulation)
tone tag --auto-import=covers --auto-import=chapters --path-pattern="audiobooks/%g/%a/%s/%p - %n.m4b" --path-pattern="audiobooks/%g/%a/%z/%n.m4b" audiobooks/ --dry-run

# write your own custom JavaScript tagger and call this function with parameters to modify metadata on your own
tone tag "harry-potter-1.m4b" --taggers="musicbrainz" --script="musicbrainz.js" --script-tagger-parameter="e2310769-2e68-462f-b54f-25ac8e3f1a21"


tone is a terminal application and deployed as monolithic binary with no dependencies.
This means, that downloading a single file from the releases page.

Linux / macOS

# linux-arm

# linux-arm64

# linux-x64

# macos (m1) - not working atm, see issue #6

# macos (intel)

# untar 
tar xzf tone-*.tar.gz

# install to your $PATH
sudo mv tone*/tone /usr/local/bin/

# test if tone is usable
tone --help


# download for windows (powershell)
iwr -outf

# extract tone
Expand-Archive -LiteralPath -DestinationPath .

# test if tone is usable
.tone --help

# open directory in windows explorer to manually put tone in your %PATH%, e.g. C:Windows
start .


Since tone is a monolith, it is probably not necessary to run it via docker, but since it is convenient to have a possibility to copy tone in your own image, I published an official variant on dockerhub. Since it is a multiarch image, you can use it on arm6, arm7, aarch64, and x64 images.

docker pull sandreas/tone:v0.1.4

Or to use tone in your custom Dockerfile:

# Dockerfile
FROM sandreas/tone:v0.1.4 as tone
# ...
COPY --from=tone /usr/local/bin/tone /usr/local/bin/

Reserved fields and supported formats

tone already supports some common input and output formats for metadata, as well as a tone specific one (ToneJson). Moreover tone also uses some reserved metadata fields to overcome issues when storing specific information.

Reserved metadata fields

The namespace ----:com.pilabor.tone as well as the following fields are reserved for tone in mp4 / m4a / m4b based file formats:

  • ----:com.pilabor.tone:AUDIBLE_ASIN: Since there is no official field for storing the audible ASIN, tone MAY use this custom field to store this piece information
  • ----:com.pilabor.tone:PART: Since the movement index is often used for a part of a series but only supports integers (e.g. 1) it cannot store some series part names (e.g. 2.1 or roman numbers like IV)
    • tone supports --meta-part parameter being a fallback for storing non integer values while coincidentally storing --meta-movement only if it is an integer value
    • Therefore it is always recommended to use the --meta-part parameter instead of --meta-movement to set the part number of a series

ToneJson format

The ToneJson format is specific for tone, can contain all supported metadata (including binary images) and looks similar to this example…


  "audio": {
    "bitrate": 320,
    "format": "MPEG Audio (Layer III)",
    "formatShort": "MPEG",
    "sampleRate": 44100.0,
    "duration": 255920.0,
    "channels": {
      "count": 2,
      "description": "Joint Stereo"
    "frames": {
      "offset": 20749,
      "length": 10236864
    "metaFormat": [
  "meta": {
    "album": "Back in Black",
    "albumArtist": "AC/DC",
    "artist": "AC/DC",
    "discNumber": 1,
    "discTotal": 1,
    "encodedBy": "LAME 3.99.5",
    "genre": "Hard Rock",
    "itunesCompilation": "no",
    "publisher": "Atlantic",
    "recordingDate": "1986-01-01T00:00:00",
    "sortArtist": "AC/DC",
    "title": "Back in Black",
    "trackNumber": 6,
    "trackTotal": 10,
    "embeddedPictures": [
        "type": 2,
        "code": 3,
        "mimetype": "image/jpeg",
        "data": "/9j/4AAQSkZJRgA...9k="
    "additionalFields": {
      "grP1": "5",
      "tmed": "CD",
      "tlan": "eng",
      "tipl": "arranger",
      "tdor": "1980-07-25",
      "script": "Latn",
      "artist Credit": "AC/DC",
      "albumartistsort": "AC/DC",
      "catalognumber": "16018-2",
      "album Artist Credit": "AC/DC",
      "musicBrainz Album Type": "album",
      "replaygaiN_ALBUM_GAIN": "-8.43 dB",
      "replaygaiN_ALBUM_PEAK": "1.064363",
      "replaygaiN_TRACK_GAIN": "-8.38 dB",
      "replaygaiN_TRACK_PEAK": "1.051585",
      "musicBrainz Album Status": "Official",
      "musicBrainz Album Release Country": "DE",
      "acoustid Id": "8b379144-9a9d-4fc1-897a-a7c0771f8ebb",
      "musicBrainz Album Id": "fdabb997-b984-4097-bd3b-89fafd5e2e75",
      "ufid": "http://musicbrainz.orgu0000ef71afb6-5e51-41df-999b-9e7c7306063a",
      "musicBrainz Artist Id": "66c662b6-6e2f-4930-8610-912e24c63ed1",
      "musicBrainz Album Artist Id": "66c662b6-6e2f-4930-8610-912e24c63ed1",
      "musicBrainz Release Group Id": "d3bc1a64-7561-3787-b680-0003aa50f8f1",
      "musicBrainz Release Track Id": "cf05ab29-27c7-47ed-9450-9f4de676cded",
      "acoustid Fingerprint": "AQADtE...oIIYgRUChBhABIEeWAA0AQR4hSDg",
      "iTunNORM": " 00001AE7 00001AE7 00004340 00004340 00000000 00000000 0000869A 0000869A 00000000 00000000"
  "file": {
    "size": 10257613,
    "created": "2019-06-12T18:50:37.5527895+02:00",
    "modified": "2019-06-12T18:50:37.5527895+02:00",
    "accessed": "2023-02-14T09:21:29.2261032+01:00",
    "path": "music/album/AC_DC/Back in Black",
    "name": "06 - Back in Black.mp3"

ChptFmtNative format (also CHPT_FMT_NATIVE)

The ChptFmtNative format was initially used in mp4v2, but never fully specified. However, there is a loose spec here.


## artist: Cœur de pirate
## album: Blonde
## total-duration: 00:38:37.034
00:00:00.000 Lève les voiles
00:01:12.709 Adieu
00:03:40.346 Danse et danse
00:06:50.775 Golden Baby
00:09:57.772 Ava
00:13:14.657 Loin d'ici
00:15:58.494 Les amours dévouées
00:18:26.443 Place de la république
00:22:37.664 Cap diamant
00:25:20.925 Verseau
00:29:14.722 Saint-Laurent
00:32:29.519 La petite mort
00:36:19.140 Hôtel amour

ffmetadata format

The ffmetadata format was designed for ffmpeg, a versatile media encoder and it is specified here.


title=Back in Black
album=Back in Black
genre=Hard Rock
encoded_by=LAME 3.99.5
Artist Credit=AC/DC


The features of tone are divided by commands. You can dump information or tag a file and so on. To do so, run


tone dump "my-audio-file.mp3"

global options

There are some global options, that can be used to change the behaviour of the file iterator. These options apply for all commands:

  • --order-by: Sort files by attribute (defaults to path, available options are path, size, filename, extension, created, modified, accessed, combine via ,, descending via !), examples:
    • --order-by="!created" – sort by create date descending
    • --order-by="extension,created" – sort by extension, then by created
    • --order-by="size,!extension,modified" – sort by size, then extension descending, then by modification date
  • --limit: Limit results
    • one value (e.g. --limit=10) – top 10 results
    • two values with comma (e.g. --limit=10,20) – offset 10 fetch 20 results
  • --include-extensions: Filter for these extensions
  • --debug: Enable debug mode (for development or issue reporting)
  • --force: Try to force action (e.g. overwrite existing files, etc.)

dump – show audio metadata

The dump command can be used to show metadata for a wide variety of audio files. You can either specify a single file or a directory,
which will be traversed recursively. Several output --format options are supported. By default a terminal user interface library is used,
but it is also possible to use json or ffmetadata.

Options reference

tone dump --help           
    tone dump [input] [OPTIONS]

    tone dump --help
    tone dump input.mp3
    tone dump audio-directory/ --include-extension m4b --format ffmetadata --include-property title --include-property artist

    [input]    Input files or folders

    -h, --help                 Prints help information

tag – modify audio metadata

The tag command can be used to modify audio metadata. Besides using predefined parameters like --meta-album it is also possible to
add or modify custom fields via --meta-additional-field, e.g. --meta-additional-field "©st3=testing" as well as pictures or chapters.

The --taggers option

The --taggers option allows you to specify a custom set or a different order of internal taggers (NOT input formats), which are gonna be applied. In most cases
changing the order of the taggers does not make a huge difference, but fully understanding this option
requires a bit of technical knowledge. Lets go through a use case to see what you can do with it.

Note: Internal taggers are applied in a sane order by default and not meant for beginners. Most of the time you don’t need to change the order and this usually is for very specific experts use cases. So if you don’t fully understand this option, just leave it as is.

Use case: re-tag sorttitle / sortalbum
The following taggers are relevant for this use case:

  • remove – Removes metadata fields or sets it to an empty value
  • m4bfillup – Fills up missing or relevant special fields for audio books (e.g. sorttitle / sortalbum)
  • * – Represents all remaining taggers, that are not already provided by name

Usually, the remove tagger is applied at last. If you provide --meta-remove-property=sorttitle, this ensures an existing value will really be
removed after all taggers have been applied. The m4bfillup tagger will automatically generate sorttitle / sortalbum from movementname,
movement and title / album if AND ONLY IF the current value is empty.

So if you change the movementname (e.g. Harray Potter to Harry Potter because of a typo), sorttitle / sortalbum will not be updated,
because these fields already have a value. If you remove the sorttitle / sortalbum, it will not be auto-updated but only removed,
since remove is applied after m4bfillup.

This can be solved by reordering the taggers:

  • First apply remove tagger to remove sorttitle / sortalbum completely
  • Then apply m4bfillup to rebuild sorttitle / sortalbum
tone tag harry-potter-1.m4b --taggers="remove,m4bfillup" --meta-movement-name="Harry Potter" --meta-remove-property="sortalbum" --meta-remove-property="sorttitle"

As you see, most of the time, you only care about one special tagger to be applied first or last. This is why tone has an option to add all
remaining taggers to the list using a *:

tone tag harry-potter-1.m4b --taggers="remove,*" --meta-movement-name="Harry Potter" --meta-remove-property="sortalbum" --meta-remove-property="sorttitle"

The following taggers are available at the moment (names can be applied case insensitive):

  • ToneJson – sets metadata values from tone.json file
  • Metadata – sets metadata values from input parameters --meta-...
  • Cover – sets cover from cover files
  • PathPattern – sets metadata values from path pattern
  • ChptFmtNative – sets chapters from chapters.txt file
  • Equate – equates 2 or more metadata fields from --meta-equate
  • M4BFillUp – auto fill album, title, iTunesMediaType from existing fields if possible
  • PrependMovementToDescription – prepends movement to all description fields, if set
  • Remove – removes metadata values from input parameter --meta-remove-property and --meta-remove-additional-field
  • ScriptTagger – your personal custom JavaScript taggers (see below)

Options reference

tone tag --help                                                                                                                                                                     
    tone tag [input] [OPTIONS]

    tone tag --help
    tone tag input.mp3 --meta-title "a title"
    tone tag --debug --auto-import=covers --meta-additional-field ©st3=testing input.m4b --dry-run
    tone tag --auto-import=covers --auto-import=chapters --path-pattern="audiobooks/%g/%a/%s/%p - %n.m4b" --path-pattern="audiobooks/%g/%a/%z/%n.m4b" audiobooks/ --dry-run
    tone tag input.mp3 --script musicbrainz.js --script-tagger-parameter e2310769-2e68-462f-b54f-25ac8e3f1a21

    [input]    Input files or folders

    -h, --help                               Prints help information
    -y, --assume-yes                                                
    -p, --path-pattern                                              

filename to tag via --path-pattern / -p

It is possible to use the tag subcommand with multiple --path-pattern arguments to read metadata from path names. Please note:

  • If multiple path patterns are present, the first matching one is preferred
  • Path patterns can be applied recursively for a whole directory tree as well as for single files
  • It is recommended use the --dry-run flag to see a diff before changing anything
    • there is an issue with flags like --dry-run, that they sometimes not work depending on the position – sometimes shifting them around helps
  • Path pattern matching is based on, so all metadata properties could be read from a path name and there are a lot of things yet to be documented
    • For now it is recommended to use the short hands below

short hands

All short hands are configured to match non-slash (/) or part numbers ([0-9-.IVXLCDM]+).

  • %aArtist
  • %ASortArtist
  • %cComment
  • %CCopyright
  • %dDescription
  • %DLongDescription
  • %gGenre
  • %mAlbum
  • %MSortAlbum
  • %nTitle
  • %NSortTitle
  • %pPart (only matching part numbers)
  • %sMovementName
  • %tAlbumArtist
  • %wComposer
  • %yReleaseDate
  • %zIgnoreDummy
  • %ZIgnoreDummy (only matching part numbers)

Custom scripted taggers (experimental)

With tone v0.0.4 it is possible to use scripted taggers. Long story short: You can now use JavaScript
to hook into the tagging mechanism and write your own extensions for tone.

Note: script support is limited to a specific subset of JavaScript and does not support every feature that is supported in modern browsers. If you would like to know more, take a look at jint

create a javascript file

Lets say you would like to consume an external API to set some tags, in our example we use to tag the audiobook Harry Potter and the Philosopher�s Stone :

); return; } var url = "" + id + "?inc=recordings&fmt=json"; console.log("fetching url:", url); // User-Agent header is required for musicbrainz to provide a response var json = tone.Fetch(url, { headers: { 'User-Agent': 'Mozilla/5.0 (iPad; U; CPU OS 3_2 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Version/4.0.4' } }); // you could also read a text file in the base path of the audio file // json = tone.ReadTextFile(metadata.BasePath + "/musicbrainz.json"); var result = JSON.parse(json); metadata.Title = result.title; console.log("new title:", result.title); if('barcode' in result) { metadata.AdditionalFields["ISBN"] = result.barcode; console.log("new barcode:", result.barcode); } } // register your function name as tagger tone.RegisterTagger("musicbrainz");
run your tagger

Now you can use the --script parameter to load your custom JavaScript and furthermore
the --script-tagger-parameter to provide the parameters array used in the tagger function.
If you would like to prevent the default tone taggers to be applied, you can also limit the
them to your scripted one via --taggers=musicbrainz.

tone tag "harry-potter-1.m4b" --taggers="musicbrainz" --script="musicbrainz.js" --script-tagger-parameter="e2310769-2e68-462f-b54f-25ac8e3f1a21"
Tagger API

To get an overview of fields, that can be accessed or modified via the metadata object, you should take a look at the IMetadata interface. Not all of them are primitive types, but there are API at least some helper methods to overcome this problem (more are planned):

Method Description Notes
tone.RegisterTagger(string functionName):void Registers a custom tagger function with functionName
tone.Fetch(string url [, object? options]):string Fetches remote url contents using options inspired by original fetch API Only a small subset of options is implemented (mainly method, body and headers)
tone.Download(string url, string destinationPath [, object options]):bool Downloads a remote to using options inspired by original fetch API Returns true on success, false on error

Directories will be created recursively

Files are not overwritten by default
tone.ReadTextFile(string path):string Reads a text file completely as string
tone.WriteTextFile(string path, string content):void Writes text to a file (create file if not exists, overwrite contents)
tone.AppendTextFile(string path, string content):void Appends text to a file (create file if not exists, append contents)
tone.LimitByteLength(string message, int maxLength):string Limites text to byte length (not char length)
tone.CreateDateTime(string dateString):DateTime Creates a DateTime value from string e.g. for metadata.PublishingDate
tone.CreateTimeSpan(number milliseconds):TimeSpan Creates a TimeSpan value from string e.g. for metadata.TotalDuration
tone.CreatePicture(string path):PictureInfo Creates a PictureInfo value from a path (refer to Download) for metadata.EmbeddedPictures
tone.CreateChapter(string title, number startMs, number lengthMs [, PictureInfo picture, string subtitle, string uniqueID]):ChapterInfo Creates a ChapterInfo for metadata.Chapters

The following issues are known, part of an external library and already reported:

  • flag options (e.g. --dry-run) cannot be followed by arguments (e.g. tone tag --meta-album="album" --dry-run input.mp3) (spectre.console 825)
    • workaround: append flag options at the end (tone tag --meta-album="album" input.mp3 --dry-run)
  • --meta-* options cannot be set to empty values (spectre.console 842)
    • workaround: use --meta-remove-property instead
  • Value starting with - is mistreated as extra option (e.g. --meta-description "-5 degrees") (spectre.console 890)
    • workaround: use --meta-description="-5 degrees" instead (with =)
  • Invalid handling of parameter values starting with double quotes (“), e.g. --meta-description'"quoted" value' (spectre.console 891)
  • Invalid handling of --meta-recording-date="2022-07-05" (atldotnet 155)

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By |2023-05-30T15:08:43+00:00May 30, 2023|Entertainment|0 Comments

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