I have a Sally Lightfoot in my aquarium and does not bother my corals or inverts. They are considered to be reef safe. But there are always exceptions to the rule.
I have one and she doesn't bother anything she just hangs out on the rock and sand all day.
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I had a Sally for awhile - it wiped out a good deal of the coralline in a matter of a day or two - had to take it back
One COOL crab IMO - very active !