Comment by viraptor

It's different, but close enough to not matter a lot of the time. As in, some constructs are not allowed but they're extremely rare in practice and have simple workarounds, even if you don't preserve the exact same usage syntax.

So, you extremely rarely can run Ruby code in Crystal. But simple scripts are trivial to annotate. Larger apps won't require huge changes, but you're likely to run into dependencies you also need to port.