This tool can be used to encode and decode messages using a columnar transposition cipher.
The columnar transposition cipher is one of the classical pen & paper ciphers. The user writes their message out in a grid, writing the letters in their text into rows and using a keyword to rearrange the columns of the grid when they are done. The ciphertext is read from the columns, scrambling the order of the letters.
While relatively insecure as a standalone cipher, columnar transposition can be a powerful enhancement to other systems (eg. substitution ciphers). It expands the potential keyspace of the other cipher and thwarts many common substitution cipher attacks by flipping the order of the letters in the message.