Generador de contraseñas

You are an experienced full-stack web developer. Build a web tool called "Generador de contraseñas" that meets the requirements below.

## Goal

Build a random password generator that uses a cryptographically secure random source.

## Core features

- Length from 8 to 128
- Toggle upper case, lower case, digits and symbols
- Option to exclude look-alike characters (0/O, l/1)
- Generate several at once
- Show entropy in bits and a strength label

## Inputs

- Length, character sets, count, exclusions

## Outputs

- List of passwords
- Estimated entropy in bits

## Edge cases and handling rules

- Explain that at least one character set is required
- Guarantee at least one character from each selected set
- Use crypto.getRandomValues, never Math.random
- Avoid modulo bias when picking characters

## Implementation requirements

- Build it as a single page (HTML, CSS, JavaScript) that runs entirely in the browser, and never send the user's input to a server.
- Make the UI responsive and easy to use on mobile; label every input and keep everything keyboard accessible.
- Add a Copy button for results and show clear, friendly error messages for invalid input.
- Keep the core logic in functions separate from the UI so it can be unit-tested.

## Definition of done (test cases)

- Every result has 16 characters when length is 16
- Only digits appear when only digits are selected
- 12 characters from 94 shows about 79 bits

First outline your implementation plan in at most five lines, then write the complete code, and finally explain how to check the test cases above.

---
name: build-password-generator
description: Use when building or changing a Generador de contraseñas tool. Build a random password generator that uses a cryptographically secure random source.
---

# Build: Generador de contraseñas

## Goal

Build a random password generator that uses a cryptographically secure random source.

## Workflow

1. Review the required features, inputs and outputs below and ask about anything missing first.
2. Implement the core logic as pure functions separate from the UI.
3. Check the logic against the test cases in the verification list.
4. Build a responsive UI with an input form, a result area and a Copy button.
5. Reproduce each edge case listed under Rules and refine the error messages.

## Core features

- Length from 8 to 128
- Toggle upper case, lower case, digits and symbols
- Option to exclude look-alike characters (0/O, l/1)
- Generate several at once
- Show entropy in bits and a strength label

## Inputs

- Length, character sets, count, exclusions

## Outputs

- List of passwords
- Estimated entropy in bits

## Rules

- Explain that at least one character set is required
- Guarantee at least one character from each selected set
- Use crypto.getRandomValues, never Math.random
- Avoid modulo bias when picking characters
- Build it as a single page (HTML, CSS, JavaScript) that runs entirely in the browser, and never send the user's input to a server.

## Verification

- [ ] Every result has 16 characters when length is 16
- [ ] Only digits appear when only digits are selected
- [ ] 12 characters from 94 shows about 79 bits