Generally names have a 50/100 character limit, depending on context.
Descriptions have a limit of 250 characters.
Fields like question instructions or rationales etc. are to all intents and purposes unlimited (though the limit is actually 16Mb).
Comments/task comments - 2000 characters
Character limits when setting up projects
Project name - 100
Short description - 200
Exercise - 50 (per exercise)
When creating an exercise if you go over the character limit (50) the following error message is displayed: