# Password Strength Meter

## Objective

Show whether a password is actually hard to guess, and how to fix it.

A live strength indicator based on guessability — length, common passwords, and terms drawn from the user's own details — with specific advice.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Score guessability, not character classes. 'P@ssw0rd1' satisfies every composition rule and is one of the first guesses any attacker makes.
2. Penalise the user's own email, name, workspace and product name — those are the first things a targeted attacker tries.
3. Give one concrete suggestion at a time, tied to the actual weakness. 'Add a symbol' is theatre; 'this is a common password' is useful.
4. Evaluate entirely in the app. Never send a password, or anything derived from it that could be reversed, to a third-party service.
5. Do not let the meter and the server disagree. If the server rejects something the meter called strong, the meter is lying — derive both from the same policy.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- The meter must be advisory unless server policy sets a real minimum; blocking on a subjective score frustrates people using password managers.
- Very long passphrases must score well even without symbols or digits.
- Pasted passwords from a manager must be scored the same as typed ones, and paste must not be blocked.
- A large common-password list must not be shipped in a way that stalls the first keystroke — load it lazily or check server-side.
- The score must be announced to assistive technology, and must not rely on colour alone to signal weakness.
- Never log, echo, or include the password in error reports while scoring it.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Scoring accounts for length, common passwords, and user-specific terms.
- [ ] Client feedback and server acceptance come from the same policy and never contradict each other.
- [ ] No password data leaves the application.
- [ ] Long passphrases score strongly without symbol requirements.
- [ ] The strength level is conveyed by text as well as colour and is announced to screen readers.
- [ ] Paste is allowed and scored identically to typing.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.