# Preact

The `preact` challenge sends the browser a simple challenge that makes it run very lightweight JavaScript that proves the client is able to execute client-side JavaScript. It uses [Preact](https://www.npmjs.com/package/preact) (a lightweight client side web framework in the vein of React) to do this.

To use it in your Anubis configuration:

```yaml
# Generic catchall rule
- name: generic-browser
  user_agent_regex: >-
    Mozilla|Opera
  action: CHALLENGE
  challenge:
    difficulty: 1 # Number of seconds to wait before refreshing the page
    algorithm: preact
```

This is the default challenge method for most clients.