git-annex allows you to store arbitrary metadata about files stored in the git-annex repository. The metadata is stored in the git-annex branch, and so is automatically kept in sync with the rest of git-annex's state, such as location tracking information.

Some of the things you can do with metadata include:

• Using git annex metadata file to show all the metadata associated with a file.
• metadata driven views
• Limiting the files git-annex commands act on to those with or without particular metadata. For example git annex find --metadata tag=foo --or --metadata tag=bar
• Using it in preferred content expressions. For example "tag=important or not author=me"

Each file (actually the underlying key) can have any number of metadata fields, which each can have any number of values. For example, to tag files, the tag field is typically used, with values set to each tag that applies to the file.

The field names are limited to alphanumerics (and [_-.]), and are case insensitive. The metadata values can contain absolutely anything you like -- but you're recommended to keep it simple and reasonably short.

Here are some recommended metadata fields to use:

• tag - With each tag being a different value.
• year, month - When this particular version of the file came into being.

To make git-annex automatically set the year and month when adding files, run git config annex.genmetadata true. Also, see automatically adding metadata.

git-annex's metadata can be updated in a distributed fashion. For example, two users, each with their own clone of a repository, can set and unset metadata at the same time, even for the same field of the same file. When they push their changes, git annex merge will combine their metadata changes in a consistent and (probably) intuitive way.

See the metadata design page for more details.