kotlin-specialist
Provides idiomatic Kotlin implementation patterns including coroutine concurrency, Flow stream handling, multiplatform architecture, Compose UI construction, Ktor server setup, and type-safe DSL design. Use when building Kotlin applications requiring coroutines, multiplatform development, or Android with Compose. Invoke for Flow API, KMP projects, Ktor servers, DSL design, sealed classes, suspend function, Android Kotlin, Kotlin Multiplatform.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/jeffallan/claude-skills --skill kotlin-specialist- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads kotlin-specialist automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Kotlin Specialist
Senior Kotlin developer with deep expertise in coroutines, Kotlin Multiplatform (KMP), and modern Kotlin 1.9+ patterns.
Core Workflow
- Analyze architecture - Identify platform targets, coroutine patterns, shared code strategy
- Design models - Create sealed classes, data classes, type hierarchies
- Implement - Write idiomatic Kotlin with coroutines, Flow, extension functions
- Checkpoint: Verify coroutine cancellation is handled (parent scope cancelled on teardown) and null safety is enforced before proceeding
- Validate - Run
detektandktlint; verify coroutine cancellation handling and null safety- If detekt/ktlint fails: Fix all reported issues and re-run both tools before proceeding to step 5
- Optimize - Apply inline classes, sequence operations, compilation strategies
- Test - Write multiplatform tests with coroutine test support (
runTest, Turbine)
Reference Guide
Load detailed guidance based on context:
| Topic | Reference | Load When |
|---|---|---|
| Coroutines & Flow | references/coroutines-flow.md | Async operations, structured concurrency, Flow API |
| Multiplatform | references/multiplatform-kmp.md | Shared code, expect/actual, platform setup |
| Android & Compose | references/android-compose.md | Jetpack Compose, ViewModel, Material3, navigation |
| Ktor Server | references/ktor-server.md | Routing, plugins, authentication, serialization |
| DSL & Idioms | references/dsl-idioms.md | Type-safe builders, scope functions, delegates |
Key Patterns
Sealed Classes for State Modeling
sealed class UiState<out T> {
data object Loading : UiState<Nothing>()
data class Success<T>(val data: T) : UiState<T>()
data class Error(val message: String, val cause: Throwable? = null) : UiState<Nothing>()
}
// Consume exhaustively — compiler enforces all branches
fun render(state: UiState<User>) = when (state) {
is UiState.Loading -> showSpinner()
is UiState.Success -> showUser(state.data)
is UiState.Error -> showError(state.message)
}
Coroutines & Flow
// Use structured concurrency — never GlobalScope
class UserRepository(private val api: UserApi, private val scope: CoroutineScope) {
fun userUpdates(id: String): Flow<UiState<User>> = flow {
emit(UiState.Loading)
try {
emit(UiState.Success(api.fetchUser(id)))
} catch (e: IOException) {
emit(UiState.Error("Network error", e))
}
}.flowOn(Dispatchers.IO)
private val _user = MutableStateFlow<UiState<User>>(UiState.Loading)
val user: StateFlow<UiState<User>> = _user.asStateFlow()
}
// Anti-pattern — blocks the calling thread; avoid in production
// runBlocking { api.fetchUser(id) }
Null Safety
// Prefer safe calls and elvis operator
val displayName = user?.profile?.name ?: "Anonymous"
// Use let to scope nullable operations
user?.email?.let { email -> sendNotification(email) }
// !! only when the null case is a true contract violation and documented
val config = requireNotNull(System.getenv("APP_CONFIG")) { "APP_CONFIG must be set" }
Scope Functions
// apply — configure an object, returns receiver
val request = HttpRequest().apply {
url = "https://api.example.com/users"
headers["Authorization"] = "Bearer $token"
}
// let — transform nullable / introduce a local scope
val length = name?.let { it.trim().length } ?: 0
// also — side-effects without changing the chain
val user = createUser(form).also { logger.info("Created user ${it.id}") }
Constraints
MUST DO
- Use null safety (
?,?.,?:,!!only when contract guarantees non-null) - Prefer
sealed classfor state modeling - Use
suspendfunctions for async operations - Leverage type inference but be explicit when needed
- Use
Flowfor reactive streams - Apply scope functions appropriately (
let,run,apply,also,with) - Document public APIs with KDoc
- Use explicit API mode for libraries
- Run
detektandktlintbefore committing - Verify coroutine cancellation is handled (cancel parent scope on teardown)
MUST NOT DO
- Block coroutines with
runBlockingin production code - Use
!!without documented justification - Mix platform-specific code in common modules
- Skip null safety checks
- Use
GlobalScope.launch(use structured concurrency) - Ignore coroutine cancellation
- Create memory leaks with coroutine scopes
Output Templates
When implementing Kotlin features, provide:
- Data models (sealed classes, data classes)
- Implementation file (extension functions, suspend functions)
- Test file with coroutine test support
- Brief explanation of Kotlin-specific patterns used
Knowledge Reference
Kotlin 1.9+, Coroutines, Flow API, StateFlow/SharedFlow, Kotlin Multiplatform, Jetpack Compose, Ktor, Arrow.kt, kotlinx.serialization, Detekt, ktlint, Gradle Kotlin DSL, JUnit 5, MockK, Turbine
Maintained by @jeffallan, Principal Consultant at Synergetic Solutions
FAQ
What does the kotlin-specialist skill do?
Provides idiomatic Kotlin implementation patterns including coroutine concurrency, Flow stream handling, multiplatform architecture, Compose UI construction, Ktor server setup, and type-safe DSL design. Use when building Kotlin applications requiring coroutines, multiplatform development, or Android with Compose. Invoke for Flow API, KMP projects, Ktor servers, DSL design, sealed classes, suspend function, Android Kotlin, Kotlin Multiplatform.
How do I install kotlin-specialist?
Run npx skills add https://github.com/jeffallan/claude-skills --skill kotlin-specialist in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/kotlin-specialist/ (personal) or .claude/skills/kotlin-specialist/ (project).
Which AI agents can use kotlin-specialist?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is kotlin-specialist safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; Runlayer passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains kotlin-specialist?
It is published by jeffallan in jeffallan/claude-skills. It has 5,195 recorded installs.
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