ASCII tab

Description
ASCII tablature is a human-readable format designed to store the information necessary for playing songs on a range of instruments - predominantly guitar, bass guitar and drums, but it has also been used for other instruments including mandolin and harmonica.

It is perhaps debatable to label it a format, as there is no formal specification as such; rather, there are a series of more-or-less codified practices and conventions for each instrument. In addition to these general conventions, ASCII tabs will often include freeform information such as lyrics or transcription notes.

Information
While - as noted above - there is no formal specification for ASCII tablature, we will attempt here to document some of the conventions of form and notation for various instruments.

Guitar / Bass
Guitar is by far the most popular instrument for which ASCII tabs are used and, as such, perhaps the instrument which suffers worst from variations in format. However, there are certain more-or-less universal conventions (although no doubt if you search long and hard enough, you will encounter files which vary or break these).

The basic structure will look something like this:

The letters at the side denote the six strings of the guitar from top (thinnest) to bottom (thickest) - these are often omitted, or may use different letters depending on the required tuning (this may also be denoted in some other fashion). The numbers on the strings denote the position of the player's fingers on the frets.