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Slider Captcha

English | 中文

The user completes the verification by dragging the slider to support the PC and mobile terminals. The time, accuracy and sliding trajectory information of user dragging behavior can be sent to the server, and then the background algorithm verification can be carried out.

Blazor Version


Online Demonstration

Single page presentation: http://longbowenterprise.gitee.io/slidercaptcha/
In-Project Demonstration: https://admin.blazor.zone/ (Open source Admin Control Pannel [BootstrapAdmin])
Slide captcha appears for the fourth time after three times of incorrect password input


输入图片说明 输入图片说明

Quick Start




<link href="https://cdn.bootcss.com/font-awesome/5.7.2/css/all.min.css">
<link href="./src/slidercaptcha.css">

Copy-paste the stylesheet <link> into your <head> before all other stylesheets to load our CSS.


<script src="./src/longbow.slidercaptcha.js"></script>

Place the following <script>s near the end of your pages, right before the closing </body> tag, to enable them.


<div id="captcha"></div>


JavaScript behavior

<div id="captcha"></div>
        id: 'captcha'


<div id="captcha"></div>
        id: 'captcha',
        width: 280,
        height: 150,
        sliderL: 42,
        sliderR: 9,
        offset: 5,
        loadingText: 'Loading...',
        failedText: 'Try again',
        barText: 'Slide right to fill',
        repeatIcon: 'fa fa-redo',
        setSrc: function () {
        onSuccess: function () {
        onFail: function () {

        onRefresh: function () {
Name Type Default Description
width integer 280 Background picture width
height integer 150 Background picture height
sliderL integer 42 Puzzle Width
sliderR integer 9 Puzzle Outburst Radius
offset integer 5 Validation of error tolerance deviation. default 5px
loadingText string "Loading..." Text information displayed when images are loaded
failedText string "Try again" Text information displayed when validation fails
barText integer "Slide right to fill" Text information displayed when dragging the slider to prepare for dragging
repeatIcon string "fa fa-redo" Reload icons. dependent on font-awesome
setSrc function "https://picsum.photos/?image=random" Setting the Picture Loading Path
onSuccess function null Callback this function when validation passes
onFail function null Callback this function when validation fails
onRefresh function null Callback this function when click on the reload icon
localImages function function () { return 'images/Pic' + Math.round(Math.random() * 4) + '.jpg'; } Call this function when the image loading fails


<div id="captcha"></div>
    var captcha = sliderCaptcha({
        id: 'captcha'
Method Example Description
reset captcha.reset() reset




Please go to Issue page to create issue

Verify On Server Side

Client Code Example

1. JavaScript

verify: function (arr, url) {
    var ret = false;
        url: url,
        data: JSON.stringify(arr),
        async: false,
        cache: false,
        type: 'POST',
        contentType: 'application/json',
        dataType: 'json',
        success: function (result) {
            ret = result;
    return ret;
Parameter Type Default Descript
arr array object trails of user dragging slider
url string remoteUrl option.remoteUrl

sample code

    id: 'captcha',
    repeatIcon: 'fa fa-redo',
    setSrc: function () {
        return 'https://imgs.blazor.zone/images/Pic' + Math.round(Math.random() * 136) + '.jpg';
    onSuccess: function () {
        window.location.href = 'https://gitee.com/LongbowEnterprise/SliderCaptcha';
    remoteUrl: "api/Captcha"

Server Code Example

1. NETCore WebApi

/// <summary>
/// slider verify web api
/// </summary>
public class CaptchaController : ControllerBase
    /// <summary>
    /// 服务器端滑块验证方法
    /// </summary>
    /// <returns></returns>
    public bool Post([FromBody]List<int> datas)
        var sum = datas.Sum();
        var avg = sum * 1.0 / datas.Count;
        var stddev = datas.Select(v => Math.Pow(v - avg, 2)).Sum() / datas.Count;
        return stddev != 0;

2. JAVA SpringBoot

You may have precision problems, but you can use BigDecimal optimization

public class SliderCaptchaController {

	public boolean isVerify(List<Integer> datas) {
		int sum = 0;
		for (Integer data : datas) {
			sum += data;
		double avg = sum * 1.0 / datas.size();
		double sum2 = 0.0;
		for (Integer data : datas) {
			sum2 += Math.pow(data - avg, 2);
		double stddev = sum2 / datas.size();
		return stddev != 0;


linked issue


  1. Fork this project
  2. Create new Feat_xxx branch
  3. Commit
  4. Create Pull Request
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滑块验证码,用户通过拖动滑块完成校验,支持PC端及移动端,新增 Blazor 版本的滑块验证码 expand collapse
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