The TypeError: 'int' object is not subscriptable in Python occurs when an attempt is made to index or slice an integer, which is not a subscriptable data type like lists, tuples, strings, or dictionaries. This error often arises from accidental variable reassignment or unexpected function return values that result in an integer instead of a sequence. To prevent and fix this error, it is crucial to maintain type consistency, verify variable types before subscripting, and ensure functions return expected data types. Employing defensive coding practices, such as using type hints, type checking with isinstance, and unit testing, can help mitigate this issue. Debugging and tracing tools, as well as error tracking platforms like Rollbar, offer additional support by providing insights into variable states and errors, facilitating quicker resolution.