A couple questions about my API to convert 10 digit ISBNs to 13 digits pointed out somethings I failed to mention earlier.
First, the API actually works both ways. That is, it identifies and validates both 10 and 13 digit ISBNs on input, and returns both versions in the output. Example: 0811822842 and 978081182284-8.
And, as yet, I have no user agreement or usage policy. Except for the disclaimer — don’t blame me if it’s broke — I’m leaving this open (though I’ll probably have to figure something out for future APIs).
Finally, if all you want is a one-time conversion of a list of ISBN’s, you might find Dave Pattern’s solution a bit easier.
update: EdJohnston‘s notes about why the ISBN1013 API can’t be linked from the Wikipedia ISBN page.