Kotlin Captcha

A concise, null-safe language backed by JetBrains and Google that runs wherever Java does, from Android to the cloud.Embed TrustCaptcha in Kotlin back-ends or Android apps for a privacy-friendly shield that marries proof-of-work, adaptive scoring and full design customisation.

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TrustCaptcha is the privacy friendly and user focused CAPTCHA for Kotlin

Security & Bot-ScoreTrustCaptcha combines a proof-of-work with a bot score — similar to the reCAPTCHA score — and custom security configurations for maximum security. Learn more about the CAPTCHA security concept

Privacy Friendly & GDPR-CompliantTrustCaptcha is a privacy-first CAPTCHA solution with a clear focus on data protection and GDPR compliance. Learn more about the GDPR-compliant CAPTCHA

CustomizationAll features of the CAPTCHA widget are fully customizable such as translations or design. The branding or the entire widget can also be hidden. Learn more about the customization

AccessibilityThe CAPTCHA completely dispenses with puzzles or image marking tasks. The CAPTCHA works fully automated and complies with international accessibility standards. Learn more about the accessibility

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Integrate TrustCaptcha in Kotlin

Integrate TrustCaptcha with Kotlin quickly and easily into your website, application or platform in just a few steps and effectively protect your online presence and services from bot abuse.

1 – Sign in or sign up
The first thing you need to do is sign in to your Trustcomponent account. If you do not yet have a Trustcomponent account, you can register with us quickly and easily in just a few steps. After that, go to your dashboard. Here you will see all existing CAPTCHAs and can create new CAPTCHAs.
2 – Choose existing CAPTCHA or create a new CAPTCHA
If you already have a CAPTCHA that you want to use, skip this step. If you don't have a CAPTCHA yet, create a new CAPTCHA now.Create a new CAPTCHADuring the creation process, select the “TrustCaptcha” product category and choose your preferred pricing plan. If you are not yet sure which pricing plan to choose, no problem! The plan can be extended at any time. Then decide whether you want to start with the 30-day trial version or go straight to a paid subscription. If you want to start directly with a paid CAPTCHA, all you have to do is add your billing details and optionally a payment method and you're ready to go.30-day trail periodIf you opt for the 30-day trial period, you can test CAPTCHA for 30 days risk-free. At the end of the 30-day trial period, CAPTCHA locks itself. During the 30-day trial period or up to 30 days after the end of the trial period, you can unsubscribe from CAPTCHA at any time for a fee or delete it with immediate effect. If you neither subscribe to the CAPTCHA for a fee nor delete it within 30 days of the end of the free trial period, it will be deleted automatically.Non-Commercial PlanIn addition to our standard plans, we also offer a permanently free “Non Commercial“ plan with 1 website and up to 500 free verifications for non-commercial websites and projects.
3 – Add your websites and check your credentials
On the dashboard of your CAPTCHA you will find all the important information, statistics and setting options. Here you will also find your site-key, the secret-key and, if available, the license-key. You will need these later on when integrating your CAPTCHA.Add your websitesYour CAPTCHA may only be accessed by websites that you explicitly authorise. To allow websites to access the CAPTCHA, enter all the websites on which you want to integrate the CAPTCHA in the settings.
4 – Solve the CAPTCHA in your frontend
Integrate the CAPTCHA widget into your website or app. You can find detailed instructions for the frontend integration in our documentation. The CAPTCHA widget will then be displayed on your website or app.
Prebuild frontend integrationsYou can use one of our pre-built integrations to integrate the CAPTCHA widget into your website or application. If there is no pre-built integration from us for your preferred frontend technology, your software developers can integrate the CAPTCHA themselves using our documentation or ask our support-team for a pre-built integration solution.
5 – Validate the CAPTCHA result in your backend
When the CAPTCHA has finished, take the verification token and send it to your backend. Then retrieve the verification result from our servers and determine your next steps. You can find detailed information on backend integration in our documentation.Basic steps for KotlinThe basic steps for your Kotlin integration are as follows. For detailed instructions, please read our documentation.Install Dependency
Select a tab
MavenGradle GroovyGradle KotlinGradle Sbt
Fetch Result
Select a tab
Fetch Result
Handle Result
Select a tab
Handle Result
Other backend technology instead of Kotlin?If you do not want to use Kotlin or have several backend services you can select a different language or framework here. If there is no pre-built integration from us for your preferred backend technology, your software developers can integrate the CAPTCHA themselves using our documentation or ask our support-team for a pre-built integration solution.
6 – Congratulations 🎉
You are now protected by TrustCaptcha - congratulations!

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Frequently Asked Questions

What is a Kotlin CAPTCHA?

A Kotlin CAPTCHA is a human-verification challenge you embed in Kotlin-based websites, APIs or mobile back-ends to keep out automated scripts and fraud. TrustCaptcha provides a JVM-native library and a self-running widget that issues a cryptographically signed token your Kotlin server can verify in one line of code. Because the SDK is JVM-native, it integrates seamlessly with Spring Boot, Ktor, Micronaut and other Kotlin stacks.

What is the best Kotlin CAPTCHA?

The best Kotlin CAPTCHA balances security, privacy and user experience, and TrustCaptcha stands out because it layers proof-of-work, an AI-driven bot-score and customizable rules rather than relying solely on proof-of-work. This multi-layered model detects 99.9 % of bots and makes automated attacks up to 30 × slower than single-layer puzzles. For European teams, its EU hosting, GDPR compliance and Kotlin-first SDK make it a future-proof choice.

How does a Kotlin CAPTCHA work?

On the client, TrustCaptcha starts automatically, solves a tiny proof-of-work puzzle whose difficulty grows with suspicious behaviour and collects lightweight device signals. These signals feed an AI that returns a bot-likelihood score, which is encrypted into the token sent to your Kotlin backend. Your server verifies the token with CaptchaManager.verify in under 100 ms and acts on the result or score threshold.

Do I need a Kotlin CAPTCHA?

If your Kotlin service exposes public forms, search boxes, login or business-critical APIs, a CAPTCHA remains the simplest first line of defence against spam, credential-stuffing and carding bots. Because TrustCaptcha runs invisibly and adds virtually no friction, you avoid the conversion losses typical of puzzle-based CAPTCHAs. Its GDPR-ready hosting also lowers legal risk for European businesses compared with US-hosted alternatives. Unlike heavy interactive CAPTCHAs, TrustCaptcha’s invisible approach still lets your FAQ pages win rich-snippet spots because it follows Google’s FAQPage schema guidelines.

Is TrustCaptcha GDPR compliant?

Yes—TrustCaptcha processes all data inside ISO 27001-certified EU data centres and never sets cookies on the client. You can conclude a Data Processing Agreement online and even enable Minimal Data Mode for highly sensitive projects. These measures help you avoid hefty GDPR fines often associated with US-based CAPTCHA providers.

Can I fully customize TrustCaptcha's appearance?

The widget supports more than 35 languages, light, dark and auto themes, custom colours, corner-radius tweaks and full whitelabel mode. You can hide branding, run the challenge invisibly, or show a subtle status badge that meets WCAG 2.2 accessibility standards. Such flexibility keeps your brand consistent while boosting user trust and engagement.

Will TrustCaptcha slow down my Kotlin application?

No—its script is under 30 KB compressed and starts solving immediately, so legitimate users see no noticeable delay. Pages load up to 3 × faster and complete 7 × quicker than image-based CAPTCHAs because there are no puzzle assets to download or manual clicks to perform. Backend verification is asynchronous and typically finishes in less than 100 ms, keeping API throughput high even at scale.