Six-digit pattern
Singapore postal codes are six digits. Validation should allow leading digits and avoid US-only five-digit assumptions.
Use a numeric six-digit field.
Do not force ZIP+4 or state-based ZIP rules.
Test postal code lookup and shipping calculations separately.
Checkout validation tips
Use multiple Singapore postal codes in automated checkout runs to test address autocomplete, delivery zones, and shipping errors.
Verify mobile keyboard behavior for numeric input.
Check that postal codes do not remove unit-number fields.
Save seeded datasets for repeatable regression tests.