My favorite part of Ruby is the testability. You can test anything, easily, without having to make interfaces and other design decisions specifically around tests.

Testing anything in Ruby is dead simple, and agents are very good at writing the tests.

The REPL is also a big win for agents. Reproducing a bug, or exploring how to build a feature, agents can get a lot of mileage out of a rails console.

A lot of the developer ergonomics are just as helpful to agents.

The performance of Ruby sucks, though.