Is my password sent or stored?

It is sent once to the check endpoint over HTTPS and never persisted — only anonymised usage (tool, risk, score) is recorded. The input is cleared from the page after each check.

Is this a security guarantee?

No. It estimates strength using length, character diversity and well-known weak-password lists. Strong passwords still need unique per-service usage and safe storage.

Password Security Checker — Strength Estimate

What this checks

Length and character-set diversity (pool size).
Common weak-password heuristics (well-known lists, e.g. 123456, password…).
An estimated entropy in bits and a 0–100 strength score.

Caveats: an estimate, not a guarantee. Use unique passwords per service and a password manager; never reuse this check result as the only protection.

Related Knowledge

How Secure Is Your Password? — build strong, unique passwords.
Identity & MFA — passwords are only half of authentication.