The basic limit
In the linked American Mah Jongg Association beginner guide, Jokers may fill larger like-tile groups, but not singles or pairs. Your current card and table rules still decide the hand you are trying to complete.
Ask which group it belongs to
Check the group
Three or more like tiles
The association guide allows Jokers in a Pung, Kong, Quint, or Sextet. Check the card line and any restrictions before placing one.
Do not place it here
Singles and pairs
A Joker does not stand in for a tile in a single or pair under the linked guide.
Thinking about an exchange?
- Find an exposed group that contains a Joker.
- Identify the matching natural tile you would give in its place.
- Check that it is your turn and that your table uses the same exchange rule.
- Ask for a ruling if the group, timing, or card line is uncertain.
This is a decision checklist, not a worked legal-hand example. Exchange restrictions and edge cases require a rules reviewer and an authentic current card before we illustrate them.