diff --git a/KeyboardsBot/KeyboardsBotLib/build.gradle b/KeyboardsBot/KeyboardsBotLib/build.gradle
index bda3692..8abfe8a 100644
--- a/KeyboardsBot/KeyboardsBotLib/build.gradle
+++ b/KeyboardsBot/KeyboardsBotLib/build.gradle
@@ -9,7 +9,7 @@ buildscript {
 }
 
 plugins {
-    id "org.jetbrains.kotlin.multiplatform" version "$kotlin_version"
+    id "org.jetbrains.kotlin.multiplatform"
 }
 
 
diff --git a/ResenderBot/ResenderBotLib/build.gradle b/ResenderBot/ResenderBotLib/build.gradle
index 21b03ee..1d40c3e 100644
--- a/ResenderBot/ResenderBotLib/build.gradle
+++ b/ResenderBot/ResenderBotLib/build.gradle
@@ -9,7 +9,7 @@ buildscript {
 }
 
 plugins {
-    id "org.jetbrains.kotlin.multiplatform" version "$kotlin_version"
+    id "org.jetbrains.kotlin.multiplatform"
 }
 
 
diff --git a/WebApp/build.gradle b/WebApp/build.gradle
index 334217c..53e310e 100644
--- a/WebApp/build.gradle
+++ b/WebApp/build.gradle
@@ -9,7 +9,8 @@ buildscript {
 }
 
 plugins {
-    id "org.jetbrains.kotlin.multiplatform" version "$kotlin_version"
+    id "org.jetbrains.kotlin.multiplatform"
+    id "org.jetbrains.kotlin.plugin.serialization"
 }
 
 apply plugin: 'application'
@@ -25,6 +26,7 @@ kotlin {
         commonMain {
             dependencies {
                 implementation kotlin('stdlib')
+                implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:$serialization_version"
             }
         }
 
diff --git a/WebApp/src/commonMain/kotlin/WebAppDataWrapper.kt b/WebApp/src/commonMain/kotlin/WebAppDataWrapper.kt
new file mode 100644
index 0000000..b8bede6
--- /dev/null
+++ b/WebApp/src/commonMain/kotlin/WebAppDataWrapper.kt
@@ -0,0 +1,7 @@
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class WebAppDataWrapper(
+    val data: String,
+    val hash: String
+)
diff --git a/WebApp/src/jsMain/kotlin/main.kt b/WebApp/src/jsMain/kotlin/main.kt
index 3691e25..0640c2c 100644
--- a/WebApp/src/jsMain/kotlin/main.kt
+++ b/WebApp/src/jsMain/kotlin/main.kt
@@ -2,10 +2,8 @@ import dev.inmo.micro_utils.coroutines.launchSafelyWithoutExceptions
 import dev.inmo.tgbotapi.types.webAppQueryIdField
 import dev.inmo.tgbotapi.webapps.*
 import io.ktor.client.HttpClient
-import io.ktor.client.call.receive
 import io.ktor.client.request.*
-import io.ktor.client.statement.HttpResponse
-import io.ktor.client.statement.readText
+import io.ktor.client.statement.bodyAsText
 import io.ktor.http.*
 import io.ktor.http.content.TextContent
 import kotlinx.browser.document
@@ -13,6 +11,7 @@ import kotlinx.browser.window
 import kotlinx.coroutines.*
 import kotlinx.dom.appendElement
 import kotlinx.dom.appendText
+import kotlinx.serialization.json.Json
 import org.w3c.dom.HTMLElement
 
 fun HTMLElement.log(text: String) {
@@ -22,14 +21,38 @@ fun HTMLElement.log(text: String) {
 
 fun main() {
     console.log("Web app started")
+    val client = HttpClient()
+    val baseUrl = window.location.origin.removeSuffix("/")
+
     window.onload = {
         val scope = CoroutineScope(Dispatchers.Default)
         runCatching {
+
+            scope.launchSafelyWithoutExceptions {
+                val response = client.post("$baseUrl/check") {
+                    setBody(
+                        Json { }.encodeToString(
+                            WebAppDataWrapper.serializer(),
+                            WebAppDataWrapper(webApp.initData, webApp.initDataUnsafe.hash)
+                        )
+                    )
+                }
+                val dataIsSafe = response.bodyAsText().toBoolean()
+
+                document.body ?.appendElement("div") {
+                    textContent = if (dataIsSafe) {
+                        "Data is safe"
+                    } else {
+                        "Data is unsafe"
+                    }
+                }
+            }
+
             document.body ?.appendElement("button") {
                 addEventListener("click", {
                     scope.launchSafelyWithoutExceptions {
                         handleResult({ "Clicked" }) {
-                            HttpClient().post("${window.location.origin.removeSuffix("/")}/inline") {
+                            client.post("${window.location.origin.removeSuffix("/")}/inline") {
                                 parameter(webAppQueryIdField, it)
                                 setBody(TextContent("Clicked", ContentType.Text.Plain))
                                 document.body ?.log(url.build().toString())
diff --git a/WebApp/src/jvmMain/kotlin/WebAppServer.kt b/WebApp/src/jvmMain/kotlin/WebAppServer.kt
index 5deb2f8..b6766c3 100644
--- a/WebApp/src/jvmMain/kotlin/WebAppServer.kt
+++ b/WebApp/src/jvmMain/kotlin/WebAppServer.kt
@@ -1,4 +1,5 @@
 import dev.inmo.micro_utils.coroutines.subscribeSafelyWithoutExceptions
+import dev.inmo.micro_utils.crypto.hmacSha256
 import dev.inmo.micro_utils.ktor.server.createKtorServer
 import dev.inmo.tgbotapi.extensions.api.answers.answer
 import dev.inmo.tgbotapi.extensions.api.bot.getMe
@@ -16,7 +17,8 @@ import dev.inmo.tgbotapi.types.InlineQueries.InputMessageContent.InputTextMessag
 import dev.inmo.tgbotapi.types.webAppQueryIdField
 import dev.inmo.tgbotapi.types.webapps.WebAppInfo
 import dev.inmo.tgbotapi.utils.PreviewFeature
-import io.ktor.http.HttpStatusCode
+import dev.inmo.tgbotapi.utils.TelegramAPIUrlsKeeper
+import io.ktor.http.*
 import io.ktor.server.application.call
 import io.ktor.server.http.content.*
 import io.ktor.server.request.receiveText
@@ -24,7 +26,9 @@ import io.ktor.server.response.respond
 import io.ktor.server.routing.post
 import io.ktor.server.routing.routing
 import kotlinx.coroutines.Dispatchers
+import kotlinx.serialization.json.Json
 import java.io.File
+import java.nio.charset.Charset
 
 /**
  * Accepts two parameters:
@@ -36,7 +40,11 @@ import java.io.File
  */
 @OptIn(PreviewFeature::class)
 suspend fun main(vararg args: String) {
-    val bot = telegramBot(args.first(), testServer = args.any { it == "testServer" })
+    val telegramBotAPIUrlsKeeper = TelegramAPIUrlsKeeper(
+        args.first(),
+        testServer = args.any { it == "testServer" }
+    )
+    val bot = telegramBot(telegramBotAPIUrlsKeeper)
     createKtorServer(
         "0.0.0.0",
         8080,
@@ -56,6 +64,14 @@ suspend fun main(vararg args: String) {
                 bot.answer(queryId, InlineQueryResultArticle(queryId, "Result", InputTextMessageContent(requestBody)))
                 call.respond(HttpStatusCode.OK)
             }
+            post("check") {
+                val requestBody = call.receiveText()
+                val webAppCheckData = Json {  }.decodeFromString(WebAppDataWrapper.serializer(), requestBody)
+
+                val isSafe = telegramBotAPIUrlsKeeper.checkWebAppLink(webAppCheckData.data, webAppCheckData.hash)
+
+                call.respond(HttpStatusCode.OK, isSafe.toString())
+            }
         }
     }.start(false)
 
diff --git a/build.gradle b/build.gradle
index 56c12ba..05027b6 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,3 +1,14 @@
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+        classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlin_version"
+    }
+}
+
 allprojects {
     repositories {
         mavenLocal()
diff --git a/gradle.properties b/gradle.properties
index a0d143d..99d4793 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -7,4 +7,5 @@ org.gradle.jvmargs=-Xmx768m
 kotlin_version=1.6.21
 telegram_bot_api_version=1.1.0
 micro_utils_version=0.10.4
+serialization_version=1.3.3
 ktor_version=2.0.1