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I keep receiving "invalid-site-private-key" on my reCAPTCHA validation request

I keep receiving "invalid-site-private-key" on my reCAPTCHA validation request


maybe you guys can help me with this. I am trying to implement Recaptcha in my node.js application and no matter what I do, I keep getting "invalid-site-private-key" as a response.

Here are the things I double and double checked and tried:

  1. Correct Keys
  2. Keys are not swapped
  3. Keys are "global keys" as I am testing on localhost and thought it might be an issue with that
  4. Tested in production environment on the server - same problem

The last thing I can think of is that my POST Request to the reCAPTCHA API itself is incorrect as the concrete format of the body is not explicitly documented (the parameters are documented, I know). So this is the request body I am currently sending (the key and IP is changed but I checked them on my side):

privatekey=6LcHN8gSAABAAEt_gKsSwfuSfsam9ebhPJa8w_EV&remoteip= challenge=03AHJ_Vuu85MroKzagMlXq_trMemw4hKSP648MOf1JCua9W-5R968i2pPjE0jjDGX TYmWNjaqUXTGJOyMO3IKKOGtkeg_Xnn2UVAfoXHVQ-0VCHYPNwrj3PQgGj22EFv7RGSsuNfJCyn mwTO8TnwZZMRjHFrsglar2zQ&response=Coleshill areacce

Is there something wrong with this format? Do I have to send special headers? Am I completely wrong? (I am working for 16 hours straight now so this might be ..)

Thank you for your help!

Problem courtesy of: floriankrueger


As stated in the comments above, I was able to solve the problem myself with the help of broofa and the node-recaptcha module available at

But first, to complete the missing details from above:

  • I didn't use any module, my solution is completely self-written based on the documentation available at the reCAPTCHA website.
  • I didn't send any request headers as there was nothing stated in the documentation. Everything that is said concerning the request before they explain the necessary parameters is the following:

    "After your page is successfully displaying reCAPTCHA, you need to configure your form to check whether the answers entered by the users are correct. This is achieved by doing a POST request to Below are the relevant parameters."

    -- "How to Check the User's Answer" at

So I built a querystring myself (which is a one-liner but there is a module for that as well as I learned now) containing all parameters and sent it to the reCAPTCHA API endpoint. All I received was the error code invalid-site-private-key, which actually (as we know by now) is a wrong way of really sending a 400 Bad Request. Maybe they should think about implementing this then people would not wonder what's wrong with their keys.

These are the header parameters which are obviously necessary (they imply you're sending a form):

  • Content-Length which has to be the length of the query string
  • Content-Type which has to be application/x-www-form-urlencoded

Another thing I learned from the node-recaptcha module is, that one should send the querystring utf8 encoded.

My solution now looks like this, you may use it or built up on it but error handling is not implemented yet. And it's written in CoffeeScript.

http = require 'http'

module.exports.check = (remoteip, challenge, response, callback) ->

  privatekey = 'placeyourprivatekeyhere'

  request_body = "privatekey=#{privatekey}&remoteip=#{remoteip}&challenge=#{challenge}&response=#{response}"
  response_body = ''

  options = 

    host: ''
    port: 80
    method: 'POST'
    path: '/recaptcha/api/verify'

  req = http.request options, (res) ->

    res.setEncoding 'utf8'

    res.on 'data', (chunk) ->
      response_body += chunk

    res.on 'end', () ->
      callback response_body.substring(0,4) == 'true'

  req.setHeader 'Content-Length', request_body.length
  req.setHeader 'Content-Type', 'application/x-www-form-urlencoded'

  req.write request_body, 'utf8'

Thank you :)

Solution courtesy of: floriankrueger


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This post first appeared on Node.js Recipes, please read the originial post: here

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I keep receiving "invalid-site-private-key" on my reCAPTCHA validation request


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