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cl-recaptcha is a simple interconnection between and common-lisp. It can be used for the trivial usage of the recaptcha service.


cl-recaptcha require split-sequence and drakma. I currently load it through clbuild (you’ll have to add it to wnnp-projects) to handle the dependencies.


The simplest way to use cl-recaptcha is to get a public and private key from Set the key in cl-recaptcha, insert the needed code in your site and ask cl-recaptcha for verification. All this should look somewhat like this:

(setf cl-recaptcha:private-captcha-key “your-private-key”) (setf cl-recaptcha:public-captcha-key “your-publick-key”)

In the source of the page, insert a call to challenge where you want to have your recaptcha inserted.


Assuming you get your post-vars by (get-post-var “varname”) and the ip of the user by (get-ip-address), you can check the validity of the entry of the user by running:

(verify-captcha (get-post-var “recaptcha_challenge_field”) (get-post-var “recaptcha_response_field”) (get-ip-address))

which will return T on success and nil on failure. The second value it returns tells you something about the reason of failure.

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