Made a password strength checker that runs 100% in the browser:

• Calculates entropy bits and character space
• Estimates crack time for different attack scenarios (online brute force, GPU cluster, nation-state)
• Detects common passwords and keyboard patterns
• Gives specific improvement tips

Nothing is sent to any server. All analysis runs client-side in JavaScript.

The math is straightforward: character_space ^ length = total combinations, then divide by guesses/second for different attack types.

Also includes a list of the top 50 most common passwords to check against.

Feedback welcome — particularly around the crack time estimates. I used 10B guesses/sec for the default GPU scenario, based on hashcat benchmarks for bcrypt.