from typing import List


def findAll(txt: str, subStr: str) -> List[int]:
    """
    Find the starting indicies of all instances of subStr in txt
    """
    indexList = []
    index = 0
    while True:
        try:
            index = txt.index(subStr, index)
        except ValueError:
            break
        indexList.append(int(index))
        index += 1

    return indexList