What actually makes a password strong
Length matters more than complexity rules once you're past a basic minimum - a long, random passphrase is generally stronger and easier to remember than a short password forced through symbol requirements. This checker runs entirely in your browser; the password you type is never sent anywhere, which is also why using a password manager to generate and store genuinely random passwords is a better long-term approach than trying to come up with memorable-but-strong ones yourself.
Reading the checklist, not just the score
The overall strength label gives a quick summary, but the individual checklist items underneath are more actionable - seeing specifically which criteria your password fails (too short, no symbol, matches a known common password pattern) tells you exactly what to change, rather than leaving you to guess what would improve a vague overall grade.
Why checking against common password patterns matters
A password can technically satisfy every length and character-variety rule and still be weak if it's a known common password or an easily guessed pattern - checking against a list of the most obviously overused passwords catches this category of weakness that pure length-and-complexity math alone would miss.
Why this runs entirely client-side
Checking a password's strength requires evaluating the actual password text, which creates an obvious reason not to send it anywhere - running the whole evaluation in your browser's own JavaScript, with nothing transmitted to a server, means you can safely test a password you actually intend to use without creating a record of it anywhere.