I have tried both Django and Rails for this, and honestly, very surprisingly, Rails did much better, at least with Claude Code. This is for a rewrite of an old .net application. Claude nailed it almost perfectly with Rails, but struggled with Django. YMMV.
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Ive been pleasantly surprised by claudes ability to handle a real-world rails codebase thats 5-10 years old in various spots. We dont do a lot of ruby magic / metaprogramming, and arent particularly 'railsy' in our patterns, but its had no issues figuring things out (even the light metaprogramming we _do_ use).