Qualys SSL Labs Letter Grades Explained

A+ (Exceptional):

The highest grade, showing best-practice, modern, robust security, often including HSTS and perfect scores in sub-categories.

A (Strong):

Strong commercial security with modern protocols and ciphers, but maybe not A+ features like HSTS.

B (Adequate):

Uses some older crypto for broader compatibility but with mostly modern, strong settings.

C (Obsolete):

Uses outdated crypto with modern clients, failing best practices.

D (Security Issues):

Configuration with issues that are difficult to exploit but should be fixed.

F (Exploitable):

Serious, exploitable problems, misconfigurations, or insecure protocols.

T (In Progress/Timeout):

Test couldn't complete or timed out.

M (Name Mismatch):

The domain name does not match the certificate.

0 (No Grade / Critical Failure):

The server is so insecure or misconfigured that it cannot be graded.