A git-annex key has this format:

BACKEND[-sNNNN][-mNNNN][-SNNNN-CNNNN]--NAME

For example:

SHA256E-s31390--f50d7ac4c6b9031379986bc362fcefb65f1e52621ce1708d537e740fefc59cc0.mp3
  • The backend is one of the key-value backends, which are always upper-cased.
  • The name field at the end has a format dependent on the backend. It is always the last field, and is prefixed with "--". Unlike other fields, it may contain "-" in its content. It should not contain newline characters or "/"; otherwise nearly anything goes.
  • The "-s" field is optional, and is the size of the content in bytes.
  • The "-m" field is optional, and is the mtime of the file when it was added to git-annex, expressed as seconds from the epoch. This is currently only used by the WORM backend.
  • The "-S" and "-C" fields are only used for keys that are chunks of some other key. "-S" is the size of the chunk, and "-C" is the chunk number (starting at 1).
  • Other fields could be added in the future, if needed.

git-annex always puts the fields in the order shown above when serializing a key. Older versions of git-annex would parse keys with the fields in other orders (although the name field must always come last), but the current version requires the fields come in the order shown above.

The git annex examinekey command can be used to extract information from a key.