Types:

a = array
b = boolean
c = char
d = date (YYYY-MM-DD)
dt = datetime (YYYY-MM-DD hh:mm:ss)
f = float
i = integer
m = mixed
n = numeric
s = string
ts = timestamp (YYYY-MM-DD hh:mm:ss)
container = container in which the request or response resides

Length:

255 = This number is the length of the type.