How do I check if an annuity carrier is financially strong?

“Look up the insurer's financial-strength rating from an independent agency such as AM Best. AM Best's Secure categories are A++ and A+ (Superior), A and A- (Excellent), B++ and B+ (Good), and B and B- (Fair); the Vulnerable categories are C++/C+ (Marginal), C/C- (Weak), and D (Poor).”