The Ikebukuro Jazz Festival typically sees over 2,000 members in 230 bands showing off their skills over the spring weekend. Performances take place at a few locations all around Ikebukuro Nishiguchi Park (11 venues in total). See the official website for the full line-up and timetable (Japanese only).
Event details are taken from official sources whenever possible. It is always prudent to check the official event website before attending to make sure that there have not been any changes. If you know of an error in the calendar, then please let me know through the contact form.