preact

The preact challenge runs a small JavaScript program in the browser. It checks that the client can run JavaScript through Preact, a lightweight framework similar to React.

The browser calculates a SHA-256 response and waits before it submits the result. Each unit of difficulty adds 125 milliseconds to the browser timer. The server requires at least 80 milliseconds per unit before it accepts the result.

Configuration

Add a browser rule to the bots list:

bots:
  - name: generic-browser
    expression: userAgent.matches("Mozilla|Opera")
    action: CHALLENGE
    challenge:
      algorithm: preact
      difficulty: 1

The expression matches a User-Agent that contains Mozilla or Opera. See policies for rule order and actions. See expressions for other match conditions.