Preventing Fake Accounts

A quick guide for adding bot detection using the Filter API, which is an invisible replacement for a CAPTCHA or rate limits and can be put both in your application and on the edge.

:bulb: This guide requires that you have access to API credentials. If you don't have them at hand, we recommend following our Quickstart guide first

Client-side integration

This guide shows you how to integrate Castle into a web environment using the browser SDK, Castle.js. If a native mobile application is the primary point of interaction for your customers, you may instead want to check out our guides for integrating Castle with native mobile apps.

Step 1. Install Castle.js

Install Castle.js in your JavaScript app bundle by running npm install --save @castleio/castle-js or yarn add @castleio/castle-js. Replace the value YOUR_CASTLE_APP_ID with the actual one that you'll find in the Castle dashboard.

import * as Castle from '@castleio/castle-js'


:bulb: Castle also provides a CDN hosted version that makes it easier to quickly test the client-side integration. See this section for details on how to use it. Please note that this is not recommended for production use

Step 2. Create a request token

Whenever the user submits a request to your app, for instance during login or registration, you need to create a request_token and pass it as a parameter in the request to your server.

For standard form posts, intercept the submit event for the form you want to protect or call Castle.createRequestToken(); to generate a single-use token and pass the token to your server with the form data.

import * as Castle from '@castleio/castle-js'

Castle.createRequestToken().then( (requestToken) => {

// or
const requestToken = await Castle.createRequestToken();

// TODO: add requestToken as parameter to the outgoing request
<!-- Use the form helper to automatically insert the request token on form submit //-->
<form onsubmit="_castle('onFormSubmit', event)">
  // ....


"Single-use" in this context means that a request_token can actually be used twice per request: once for a call to the Filter API, and one for the Risk API, should you use call both for the same request.

Server-side integration

See section with available server-side SDKs

Step 1. Pass the request token to the Castle API

Provide your API Secret as well as the request token string that was passed in the request in the previous step.

See the list of Supported Events as well as the API Reference

castle =

  token = request.params['castle_request_token']
  context =

  res = castle.filter(
    event: '$registration',
    request_token: token,
    context: {
      ip: context[:ip],
      headers: context[:headers]

  if res[:risk] > 0.9
    # IMPLEMENT: Deny attempt

rescue Castle::Error => e
  # Handle error
try {
  $token = $_POST['castle_request_token'];

  $res = Castle::filter([
    'event' => '$registration',
    'request_token' => $token,
    'context' => [
      'ip' => Castle_RequestContext::extractIp(),
      'headers' => Castle_RequestContext::extractHeaders()

  if ($res->risk > 0.9) {
    // IMPLEMENT: Deny attempt

} catch (Castle_Error $e) {
  // Handle error
    token = request.form['castle_request_token'] # Using Flask
    context =

    client = Client()

    res = client.filter({
        'event': '$login',
        'request_token': token,
        'context': {
          'ip': context['ip'],
          'headers': context['headers']

    if res['risk'] > 0.9:
        # IMPLEMENT: Deny attempt

except CastleError as e:
     # Handle error
String token = request.getParameter("castle_request_token");

Castle castle = Castle.initialize();
CastleContextBuilder context = castle.contextBuilder().fromHttpServletRequest(request)

try {
  CastleResponse response = castle.client().filter(ImmutableMap.builder()
    .put(Castle.KEY_EVENT, "$login")
    .put(Castle.KEY_CONTEXT, ImmutableMap.builder()
      .put(Castle.KEY_IP, context.getIp())
      .put(Castle.KEY_HEADERS, context.getHeaders())
    .put(Castle.KEY_USER, ImmutableMap.builder()
      .put(Castle.KEY_USER_ID, user.getId())
      .put(Castle.KEY_EMAIL, user.getEmail())
      .put("username", user.getUsername())
    .put(Castle.KEY_REQUEST_TOKEN, token)
} catch (CastleRuntimeException runtimeException) {
  // Handle error

float risk = response.json()

if (risk > 0.9) {
  // IMPLEMENT: Deny attempt
try {
  var token = request.body["castle_request_token"]; // Using Express

  const castle = new Castle({ apiSecret: 'YOUR SECRET HERE' });
  const context =, {}, castle.configuration);

  const res = castle.filter({
    event: '$registration',
    request_token: token,
    user: {
    context: {
      ip: context.ip,
      headers: context.headers

  if (res.risk > 0.9) {
    // IMPLEMENT: Deny attempt
} catch (e) {


As a starting point, it's recommended that you deny any attempts where the risk score is above 0.9.

The API response can be used to write granular risk logic. Read the complete list of signals and the guide on Policies for more information.

  "risk": 0.95,
  "signals": {
    "bot_behavior": {},
    "proxy_ip": {},
    "disposable_email": {},
    "spoofed_device": {}
  "policy": {
    "action": "deny",
    "name": "Block bots",
    "id": "e14c5a8d-c682-4a22-bbca-04fa6b98ad0c",
    "revision_id": "b5cf794e-88c0-426e-8276-037ba1e7ceca"

πŸŽ‰ Congratulations! -- You have now completed a basic integration of Castle!