In one sentence
A firm assigning credit ratings to securitized debt, whose criteria shape how loans are structured and pooled.
The longer version
Rating agencies rate the bonds in a securitization, and their criteria influence loan structures, reserves, and legal opinions well before securitization. Rating agency confirmations gate certain post-closing actions.
Defeasance and some assumptions require rating agency confirmation, tying loan-level events to the securitization's rating.
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