Indexing operations on arrays, slices, or strings should use an index at most one less than the length. If the operation uses a variable index but checks the length against a constant, this may indicate a logic error which could lead to an out-of-bounds access.

Inspect the code closely to determine whether the length should be compared to the index variable instead. For loops that iterate over every element, using a range loop is better than explicit index manipulation.

The following example shows a method which checks whether slice xs is a prefix of slice ys:

A loop using an index variable i is used to iterate over the elements of xs and compare them to the corresponding elements of ys. However, the check to ensure that i is a valid index into ys is incorrectly specified as len(ys) == 0. Instead, the check should ensure that len(ys) is greater than i:

The Go Programming Language Specification: For statements.

The Go Programming Language Specification: Index expressions.