23 if they used mysql (not sure how it works with other databases) and not limited it then depending on what type they used you can write till you reached this:
TINYTEXT | 255 (2 8−1) bytes
TEXT | 65,535 (216−1) bytes = 64 KiB
MEDIUMTEXT | 16,777,215 (224−1) bytes = 16 MiB
LONGTEXT | 4,294,967,295 (232−1) bytes = 4 GiB