ASCII Tabs were the original way to share tabs on the web due to their use of just simple characters that were readable by any browser, they loaded fast, used little or no bandwidth and needed no special plug in or program to write them, just a lot of patience.
They are still used in a lot of free sites, here's how an open C major chord looks like:
C
e |-----0------|
B |-----1------|
G |-----0------|
D |-----2------|
A |-----3------|
E |------------|
There are a lot of performance symbols but not everybody follows the same coding so you'll have to check on each site (or on each tab, sometimes) for the 'right' symbols: here are some of the most important ones.
Symbol
Technique
h
hammer on
p
pull off
t, T
right hand tap
b
bend string up
r
release bend
/
slide up
\
slide down
~
vibrato
n
pick stroke down
V
pick stroke up
s
legato slide
S
shift slide
*
natural harmonic
[n]
artificial harmonic
n(n)
tapped harmonic
tr
trill
TP
tremolo picking
.
staccato
PM, M
palm muting (also written as _)
w
whammy bar
\n/
>tremolo arm dip; n = amount to dip
\n
tremolo arm down
n/
tremolo arm up
/n\
tremolo arm inverted dip
=
hold bend; also acts as connecting device for hammers/pulls
<>
volume swell (louder/softer)
x
on rhythm slash represents muted slash
o
on rhythm slash represents single note slash
·/.
pick slide
Let's write the examples we saw on the previous page in ASCII:
Up and down pick strokes
n V n V n V n V n V n V n V n V
E |----------------------------|----------------------------|----|----|
B |----------------------------|----------------------------|----|----|
G |----------------------------|--------------5--6--7--8----|----|----|
D |----------------------------|--5--6--7--8----------------|----|----|
A |--------------5--6--7--8----|----------------------------|----|----|
E |--5--6--7--8----------------|----------------------------|----|----|
We can see the lines dividing the tab in bars but we have no indication about the timing of the single notes: to read this kind of tab correctly you need written instructions or you need to know the song.