What is SilentCaptcha

SilentCaptcha is a easy to use PHP script that can be used to stop bots / non-humans from completing your forms.


  • Totally invisible to the user completing the form.
  • Forms are time stamped, if a form submission is too quick (default 5 seconds) or too slow (default 1 hour) the submission is flagged as invalid. A series of alphanumeric check digits ensure this time stamp has not been tampered with.
  • A series of invisible input fields are created, called a honeypots, if any of these are completed SilentCaptcha knows that a bot has completed your form.
  • A hidden token field is validated against the submission time, secret key and IP address.
  • IP address of user is checked against a database of known spammers and bots.
  • The users browser details are check against a list of known bad user-agents.
  • Any email addresses given by the user can be checked against a large list of known disposable / temporary email providers.
  • Zero additional input required by the user, (no silly math problems, or type the characters you see)

echo "test";



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