How do I install the Kotlin Ktor Patterns skill?

Run npx skillmds@latest add contextgo/kotlin-ktor-patterns in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

What does the Kotlin Ktor Patterns skill do?

Ktor server patterns including routing DSL, plugins, authentication, Koin DI, kotlinx.serialization, WebSockets, and testApplication testing. It is listed under Coding & Dev Tools on SkillMD.

Is Kotlin Ktor Patterns safe to use?

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Which AI agents work with Kotlin Ktor Patterns?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Kotlin Ktor Patterns free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Kotlin Ktor Patterns?

contextgo (@contextgo) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Kotlin Ktor Patterns by contextgo — Agent Skill

Name: Kotlin Ktor Patterns
Author: contextgo

Ktor Server Patterns

Comprehensive Ktor patterns for building robust, maintainable HTTP servers with Kotlin coroutines.

When to Activate

Building Ktor HTTP servers
Configuring Ktor plugins (Auth, CORS, ContentNegotiation, StatusPages)
Implementing REST APIs with Ktor
Setting up dependency injection with Koin
Writing Ktor integration tests with testApplication
Working with WebSockets in Ktor

Application Structure

Standard Ktor Project Layout

src/main/kotlin/
├── com/example/
│   ├── Application.kt           # Entry point, module configuration
│   ├── plugins/
│   │   ├── Routing.kt           # Route definitions
│   │   ├── Serialization.kt     # Content negotiation setup
│   │   ├── Authentication.kt    # Auth configuration
│   │   ├── StatusPages.kt       # Error handling
│   │   └── CORS.kt              # CORS configuration
│   ├── routes/
│   │   ├── UserRoutes.kt        # /users endpoints
│   │   ├── AuthRoutes.kt        # /auth endpoints
│   │   └── HealthRoutes.kt      # /health endpoints
│   ├── models/
│   │   ├── User.kt              # Domain models
│   │   └── ApiResponse.kt       # Response envelopes
│   ├── services/
│   │   ├── UserService.kt       # Business logic
│   │   └── AuthService.kt       # Auth logic
│   ├── repositories/
│   │   ├── UserRepository.kt    # Data access interface
│   │   └── ExposedUserRepository.kt
│   └── di/
│       └── AppModule.kt         # Koin modules
src/test/kotlin/
├── com/example/
│   ├── routes/
│   │   └── UserRoutesTest.kt
│   └── services/
│       └── UserServiceTest.kt

Application Entry Point

// Application.kt
fun main() {
    embeddedServer(Netty, port = 8080, module = Application::module).start(wait = true)
}

fun Application.module() {
    configureSerialization()
    configureAuthentication()
    configureStatusPages()
    configureCORS()
    configureDI()
    configureRouting()
}

Routing DSL

Basic Routes

// plugins/Routing.kt
fun Application.configureRouting() {
    routing {
        userRoutes()
        authRoutes()
        healthRoutes()
    }
}

// routes/UserRoutes.kt
fun Route.userRoutes() {
    val userService by inject<UserService>()

    route("/users") {
        get {
            val users = userService.getAll()
            call.respond(users)
        }

        get("/{id}") {
            val id = call.parameters["id"]
                ?: return@get call.respond(HttpStatusCode.BadRequest, "Missing id")
            val user = userService.getById(id)
                ?: return@get call.respond(HttpStatusCode.NotFound)
            call.respond(user)
        }

        post {
            val request = call.receive<CreateUserRequest>()
            val user = userService.create(request)
            call.respond(HttpStatusCode.Created, user)
        }

        put("/{id}") {
            val id = call.parameters["id"]
                ?: return@put call.respond(HttpStatusCode.BadRequest, "Missing id")
            val request = call.receive<UpdateUserRequest>()
            val user = userService.update(id, request)
                ?: return@put call.respond(HttpStatusCode.NotFound)
            call.respond(user)
        }

        delete("/{id}") {
            val id = call.parameters["id"]
                ?: return@delete call.respond(HttpStatusCode.BadRequest, "Missing id")
            val deleted = userService.delete(id)
            if (deleted) call.respond(HttpStatusCode.NoContent)
            else call.respond(HttpStatusCode.NotFound)
        }
    }
}

Route Organization with Authenticated Routes

fun Route.userRoutes() {
    route("/users") {
        // Public routes
        get { /* list users */ }
        get("/{id}") { /* get user */ }

        // Protected routes
        authenticate("jwt") {
            post { /* create user - requires auth */ }
            put("/{id}") { /* update user - requires auth */ }
            delete("/{id}") { /* delete user - requires auth */ }
        }
    }
}

Content Negotiation & Serialization

kotlinx.serialization Setup

// plugins/Serialization.kt
fun Application.configureSerialization() {
    install(ContentNegotiation) {
        json(Json {
            prettyPrint = true
            isLenient = false
            ignoreUnknownKeys = true
            encodeDefaults = true
            explicitNulls = false
        })
    }
}

Serializable Models

@Serializable
data class UserResponse(
    val id: String,
    val name: String,
    val email: String,
    val role: Role,
    @Serializable(with = InstantSerializer::class)
    val createdAt: Instant,
)

@Serializable
data class CreateUserRequest(
    val name: String,
    val email: String,
    val role: Role = Role.USER,
)

@Serializable
data class ApiResponse<T>(
    val success: Boolean,
    val data: T? = null,
    val error: String? = null,
) {
    companion object {
        fun <T> ok(data: T): ApiResponse<T> = ApiResponse(success = true, data = data)
        fun <T> error(message: String): ApiResponse<T> = ApiResponse(success = false, error = message)
    }
}

@Serializable
data class PaginatedResponse<T>(
    val data: List<T>,
    val total: Long,
    val page: Int,
    val limit: Int,
)

Custom Serializers

object InstantSerializer : KSerializer<Instant> {
    override val descriptor = PrimitiveSerialDescriptor("Instant", PrimitiveKind.STRING)
    override fun serialize(encoder: Encoder, value: Instant) =
        encoder.encodeString(value.toString())
    override fun deserialize(decoder: Decoder): Instant =
        Instant.parse(decoder.decodeString())
}

Authentication

JWT Authentication

// plugins/Authentication.kt
fun Application.configureAuthentication() {
    val jwtSecret = environment.config.property("jwt.secret").getString()
    val jwtIssuer = environment.config.property("jwt.issuer").getString()
    val jwtAudience = environment.config.property("jwt.audience").getString()
    val jwtRealm = environment.config.property("jwt.realm").getString()

    install(Authentication) {
        jwt("jwt") {
            realm = jwtRealm
            verifier(
                JWT.require(Algorithm.HMAC256(jwtSecret))
                    .withAudience(jwtAudience)
                    .withIssuer(jwtIssuer)
                    .build()
            )
            validate { credential ->
                if (credential.payload.audience.contains(jwtAudience)) {
                    JWTPrincipal(credential.payload)
                } else {
                    null
                }
            }
            challenge { _, _ ->
                call.respond(HttpStatusCode.Unauthorized, ApiResponse.error<Unit>("Invalid or expired token"))
            }
        }
    }
}

// Extracting user from JWT
fun ApplicationCall.userId(): String =
    principal<JWTPrincipal>()
        ?.payload
        ?.getClaim("userId")
        ?.asString()
        ?: throw AuthenticationException("No userId in token")

Auth Routes

fun Route.authRoutes() {
    val authService by inject<AuthService>()

    route("/auth") {
        post("/login") {
            val request = call.receive<LoginRequest>()
            val token = authService.login(request.email, request.password)
                ?: return@post call.respond(
                    HttpStatusCode.Unauthorized,
                    ApiResponse.error<Unit>("Invalid credentials"),
                )
            call.respond(ApiResponse.ok(TokenResponse(token)))
        }

        post("/register") {
            val request = call.receive<RegisterRequest>()
            val user = authService.register(request)
            call.respond(HttpStatusCode.Created, ApiResponse.ok(user))
        }

        authenticate("jwt") {
            get("/me") {
                val userId = call.userId()
                val user = authService.getProfile(userId)
                call.respond(ApiResponse.ok(user))
            }
        }
    }
}

Status Pages (Error Handling)

// plugins/StatusPages.kt
fun Application.configureStatusPages() {
    install(StatusPages) {
        exception<ContentTransformationException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>("Invalid request body: ${cause.message}"),
            )
        }

        exception<IllegalArgumentException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>(cause.message ?: "Bad request"),
            )
        }

        exception<AuthenticationException> { call, _ ->
            call.respond(
                HttpStatusCode.Unauthorized,
                ApiResponse.error<Unit>("Authentication required"),
            )
        }

        exception<AuthorizationException> { call, _ ->
            call.respond(
                HttpStatusCode.Forbidden,
                ApiResponse.error<Unit>("Access denied"),
            )
        }

        exception<NotFoundException> { call, cause ->
            call.respond(
                HttpStatusCode.NotFound,
                ApiResponse.error<Unit>(cause.message ?: "Resource not found"),
            )
        }

        exception<Throwable> { call, cause ->
            call.application.log.error("Unhandled exception", cause)
            call.respond(
                HttpStatusCode.InternalServerError,
                ApiResponse.error<Unit>("Internal server error"),
            )
        }

        status(HttpStatusCode.NotFound) { call, status ->
            call.respond(status, ApiResponse.error<Unit>("Route not found"))
        }
    }
}

CORS Configuration

// plugins/CORS.kt
fun Application.configureCORS() {
    install(CORS) {
        allowHost("localhost:3000")
        allowHost("example.com", schemes = listOf("https"))
        allowHeader(HttpHeaders.ContentType)
        allowHeader(HttpHeaders.Authorization)
        allowMethod(HttpMethod.Put)
        allowMethod(HttpMethod.Delete)
        allowMethod(HttpMethod.Patch)
        allowCredentials = true
        maxAgeInSeconds = 3600
    }
}

Koin Dependency Injection

Module Definition

// di/AppModule.kt
val appModule = module {
    // Database
    single<Database> { DatabaseFactory.create(get()) }

    // Repositories
    single<UserRepository> { ExposedUserRepository(get()) }
    single<OrderRepository> { ExposedOrderRepository(get()) }

    // Services
    single { UserService(get()) }
    single { OrderService(get(), get()) }
    single { AuthService(get(), get()) }
}

// Application setup
fun Application.configureDI() {
    install(Koin) {
        modules(appModule)
    }
}

Using Koin in Routes

fun Route.userRoutes() {
    val userService by inject<UserService>()

    route("/users") {
        get {
            val users = userService.getAll()
            call.respond(ApiResponse.ok(users))
        }
    }
}

Koin for Testing

class UserServiceTest : FunSpec(), KoinTest {
    override fun extensions() = listOf(KoinExtension(testModule))

    private val testModule = module {
        single<UserRepository> { mockk() }
        single { UserService(get()) }
    }

    private val repository by inject<UserRepository>()
    private val service by inject<UserService>()

    init {
        test("getUser returns user") {
            coEvery { repository.findById("1") } returns testUser
            service.getById("1") shouldBe testUser
        }
    }
}

Request Validation

// Validate request data in routes
fun Route.userRoutes() {
    val userService by inject<UserService>()

    post("/users") {
        val request = call.receive<CreateUserRequest>()

        // Validate
        require(request.name.isNotBlank()) { "Name is required" }
        require(request.name.length <= 100) { "Name must be 100 characters or less" }
        require(request.email.matches(Regex(".+@.+\\..+"))) { "Invalid email format" }

        val user = userService.create(request)
        call.respond(HttpStatusCode.Created, ApiResponse.ok(user))
    }
}

// Or use a validation extension
fun CreateUserRequest.validate() {
    require(name.isNotBlank()) { "Name is required" }
    require(name.length <= 100) { "Name must be 100 characters or less" }
    require(email.matches(Regex(".+@.+\\..+"))) { "Invalid email format" }
}

WebSockets

fun Application.configureWebSockets() {
    install(WebSockets) {
        pingPeriod = 15.seconds
        timeout = 15.seconds
        maxFrameSize = 64 * 1024 // 64 KiB — increase only if your protocol requires larger frames
        masking = false // Server-to-client frames are unmasked per RFC 6455; client-to-server are always masked by Ktor
    }
}

fun Route.chatRoutes() {
    val connections = Collections.synchronizedSet<Connection>(LinkedHashSet())

    webSocket("/chat") {
        val thisConnection = Connection(this)
        connections += thisConnection

        try {
            send("Connected! Users online: ${connections.size}")

            for (frame in incoming) {
                frame as? Frame.Text ?: continue
                val text = frame.readText()
                val message = ChatMessage(thisConnection.name, text)

                // Snapshot under lock to avoid ConcurrentModificationException
                val snapshot = synchronized(connections) { connections.toList() }
                snapshot.forEach { conn ->
                    conn.session.send(Json.encodeToString(message))
                }
            }
        } catch (e: Exception) {
            logger.error("WebSocket error", e)
        } finally {
            connections -= thisConnection
        }
    }
}

data class Connection(val session: DefaultWebSocketSession) {
    val name: String = "User-${counter.getAndIncrement()}"

    companion object {
        private val counter = AtomicInteger(0)
    }
}

testApplication Testing

Basic Route Testing

class UserRoutesTest : FunSpec({
    test("GET /users returns list of users") {
        testApplication {
            application {
                install(Koin) { modules(testModule) }
                configureSerialization()
                configureRouting()
            }

            val response = client.get("/users")

            response.status shouldBe HttpStatusCode.OK
            val body = response.body<ApiResponse<List<UserResponse>>>()
            body.success shouldBe true
            body.data.shouldNotBeNull().shouldNotBeEmpty()
        }
    }

    test("POST /users creates a user") {
        testApplication {
            application {
                install(Koin) { modules(testModule) }
                configureSerialization()
                configureStatusPages()
                configureRouting()
            }

            val client = createClient {
                install(io.ktor.client.plugins.contentnegotiation.ContentNegotiation) {
                    json()
                }
            }

            val response = client.post("/users") {
                contentType(ContentType.Application.Json)
                setBody(CreateUserRequest("Alice", "alice@example.com"))
            }

            response.status shouldBe HttpStatusCode.Created
        }
    }

    test("GET /users/{id} returns 404 for unknown id") {
        testApplication {
            application {
                install(Koin) { modules(testModule) }
                configureSerialization()
                configureStatusPages()
                configureRouting()
            }

            val response = client.get("/users/unknown-id")

            response.status shouldBe HttpStatusCode.NotFound
        }
    }
})

Testing Authenticated Routes

class AuthenticatedRoutesTest : FunSpec({
    test("protected route requires JWT") {
        testApplication {
            application {
                install(Koin) { modules(testModule) }
                configureSerialization()
                configureAuthentication()
                configureRouting()
            }

            val response = client.post("/users") {
                contentType(ContentType.Application.Json)
                setBody(CreateUserRequest("Alice", "alice@example.com"))
            }

            response.status shouldBe HttpStatusCode.Unauthorized
        }
    }

    test("protected route succeeds with valid JWT") {
        testApplication {
            application {
                install(Koin) { modules(testModule) }
                configureSerialization()
                configureAuthentication()
                configureRouting()
            }

            val token = generateTestJWT(userId = "test-user")

            val client = createClient {
                install(io.ktor.client.plugins.contentnegotiation.ContentNegotiation) { json() }
            }

            val response = client.post("/users") {
                contentType(ContentType.Application.Json)
                bearerAuth(token)
                setBody(CreateUserRequest("Alice", "alice@example.com"))
            }

            response.status shouldBe HttpStatusCode.Created
        }
    }
})

Configuration

application.yaml

ktor:
  application:
    modules:
      - com.example.ApplicationKt.module
  deployment:
    port: 8080

jwt:
  secret: ${JWT_SECRET}
  issuer: 'https://example.com'
  audience: 'https://example.com/api'
  realm: 'example'

database:
  url: ${DATABASE_URL}
  driver: 'org.postgresql.Driver'
  maxPoolSize: 10

Reading Config

fun Application.configureDI() {
    val dbUrl = environment.config.property("database.url").getString()
    val dbDriver = environment.config.property("database.driver").getString()
    val maxPoolSize = environment.config.property("database.maxPoolSize").getString().toInt()

    install(Koin) {
        modules(module {
            single { DatabaseConfig(dbUrl, dbDriver, maxPoolSize) }
            single { DatabaseFactory.create(get()) }
        })
    }
}

Quick Reference: Ktor Patterns

Pattern	Description
`route("/path") { get { } }`	Route grouping with DSL
`call.receive<T>()`	Deserialize request body
`call.respond(status, body)`	Send response with status
`call.parameters["id"]`	Read path parameters
`call.request.queryParameters["q"]`	Read query parameters
`install(Plugin) { }`	Install and configure plugin
`authenticate("name") { }`	Protect routes with auth
`by inject<T>()`	Koin dependency injection
`testApplication { }`	Integration testing

Remember: Ktor is designed around Kotlin coroutines and DSLs. Keep routes thin, push logic to services, and use Koin for dependency injection. Test with testApplication for full integration coverage.

Kotlin Ktor Patterns

File contents

Ktor Server Patterns

When to Activate

Application Structure

Standard Ktor Project Layout

Application Entry Point

Routing DSL

Basic Routes

Route Organization with Authenticated Routes

Content Negotiation & Serialization

kotlinx.serialization Setup

Serializable Models

Custom Serializers

Authentication

JWT Authentication

Auth Routes

Status Pages (Error Handling)

CORS Configuration

Koin Dependency Injection

Module Definition

Using Koin in Routes

Koin for Testing

Request Validation

WebSockets

testApplication Testing

Basic Route Testing

Testing Authenticated Routes

Configuration

application.yaml

Reading Config

Quick Reference: Ktor Patterns

Frequently asked questions

Kotlin Ktor Patterns

File contents

Ktor Server Patterns

When to Activate

Application Structure

Standard Ktor Project Layout

Application Entry Point

Routing DSL

Basic Routes

Route Organization with Authenticated Routes

Content Negotiation & Serialization

kotlinx.serialization Setup

Serializable Models

Custom Serializers

Authentication

JWT Authentication

Auth Routes

Status Pages (Error Handling)

CORS Configuration

Koin Dependency Injection

Module Definition

Using Koin in Routes

Koin for Testing

Request Validation

WebSockets

testApplication Testing

Basic Route Testing

Testing Authenticated Routes

Configuration

application.yaml

Reading Config

Quick Reference: Ktor Patterns

Related skills

Frequently asked questions

How do I install the Kotlin Ktor Patterns skill?

What does the Kotlin Ktor Patterns skill do?

Is Kotlin Ktor Patterns safe to use?

Which AI agents work with Kotlin Ktor Patterns?

Is Kotlin Ktor Patterns free to use?

Who published Kotlin Ktor Patterns?