Enchant is called "Unbreakable" in English, my apologies.
it gives:
QuoteAt each use, there's a chance the tool's durability will not decrease.
Which means:
QuoteFor example, an Unbreaking III item has a chance to use up a use of
(100/(3+1))% = (100/4)% = 25%, so Unbreaking III should, on average,
make a tool last 4 times as long.