The idea is nice, but (as a suggestion) I would add a drop down to "strict" where you can tick whether to include 0 (zero) and 1 (one) as respectively O and I,

The idea is nice, but (as a suggestion) I would add a drop down to "strict" where you can tick whether to include 0 (zero) and 1 (one) as respectively O and I, which is what everyone would likely read as well as - maybe - 5=S while the 1 as L (as in 1337) and the 7=T are far less intuitive. To give anyone freedom of choice maybe adding a "selectively strict" button with ticks for each leet letter would be ideal (as an example I cannot read the 2 as R as it is used on http://bada55.io/ http://bada55.io/ ).