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Prove your Kotlin skills

Writing Kotlin that looks like Java with fewer semicolons is common. Lemma shows whether you write idiomatic Kotlin, through live sessions, adaptive assessments and the repositories you connect.

How Kotlin is assessed

What Kotlin competence looks like

A strong Kotlin developer uses the language as designed. Null safety is handled with intent rather than double bangs, data and sealed classes model state, and extension functions keep code readable without hiding behaviour. They choose between read-only and mutable collections deliberately.

On Android, they run work in coroutines with the right dispatcher and scope, so nothing leaks when a screen closes. They expose state from view models as flows, build UI in Jetpack Compose without needless recomposition, and know how lifecycle changes such as rotation affect what the user sees.

Kotlin session
Live · 41:07

Compose and coroutines session

60 min · Learning · with Priya R.

FeedViewModel.kt Kofi A. is sharing
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Priya R. rated the session

Practitioner · after the call

Clear reasoning on null safety. Talked through trade-offs first.

Added to KotlinAdded to record

Null safety

Nullable types, safe calls and smart casts used to remove null pointer crashes rather than hide them.

Coroutines and Flow

Scopes, dispatchers, cancellation, and flows for streaming state to the UI.

Sealed and data classes

Modelling UI state and results so every case is handled at compile time.

Jetpack Compose

Composable functions, state hoisting and avoiding unnecessary recomposition.

Android architecture

View models, repositories and dependency injection that survive lifecycle changes.

Idiomatic Kotlin

Extension functions, scope functions and collection operations used for clarity, not cleverness.

What counts as evidence of Kotlin skills?

An app store link does not say who built what. Lemma records Kotlin evidence that does: sessions with another developer, an adaptive test and repositories linked from your own account. Each entry below shows its source. See the evidence methodology for how each source is weighed.

Skills Passport
Signed
71

Kotlin

Elif Y. · SCI recomputed 9 Oct

Evidence · 4 entries

  1. Compose and coroutines session

    Live session · 9 Oct

    Rated 5.0

  2. Adaptive Kotlin assessment

    Adaptive assessment · 2 Oct

    Level 7.2

  3. A Kotlin project via GitHub

    GitHub connector · 24 Sep

    Verified

  4. Coroutine practice with the AI tutor

    AI tutor practice · 11 Sep

    Practice
Signature valid · checked today Share link
Live session

Compose and coroutines session

Build a screen or fix a coroutine bug with an Android practitioner. They rate how you manage state, scopes and lifecycle.

Adaptive assessment

Adaptive Kotlin assessment

Scenarios test null safety, coroutine cancellation and sealed class modelling. Harder rounds show a coroutine that leaks after a screen closes, and you pick the fix.

GitHub connector

A Kotlin project via GitHub

Connect an Android or server-side Kotlin repository, or a specific commit. Lemma checks it exists and that you have access.

AI tutor practice

Coroutine practice with the AI tutor

Drill scopes, dispatchers and Flow operators with adaptive exercises. Drills add a small, capped amount to practice and help you prepare for proof.

How is a Kotlin skills test run on Lemma?

The Kotlin test adapts as you go, between 15 and 25 questions on device, lifecycle and offline problems, getting harder while you answer correctly. Together with sessions and linked work it sets your Kotlin SCI, where older evidence slowly counts for less.

How the SCI score is calculatedHow adaptive skills assessments workPractise Kotlin in live skill swap sessionsWhich evidence types countWhat your Skills Passport shows
Kotlin assessment
0:42
Question 11Stops when your level holds
Difficulty7/10

A coroutine keeps updating the UI after the screen closes. It was launched in GlobalScope. What fixes it?

  1. ASwitch it to Dispatchers.IO
  2. BLaunch it in viewModelScope
  3. CWrap it in runBlocking
  4. DAdd a try/catch around the body
Locks on submit

  1. Work on a screen live

    Book a session with a Kotlin practitioner and build or debug part of an Android app. They look at your state model, coroutine scopes and how you handle configuration changes.

  2. Pass the adaptive assessment

    The Kotlin assessment moves with your answers, covering null safety, coroutines, Compose and idiomatic patterns. Harder scenarios count for more, and each one is timed.

  3. Link your repositories

    Connect Kotlin projects through GitHub so your sessions and assessment sit beside real code. Recent work keeps the skill fresh on your Passport.

Kotlin skills: common questions

How do I prove Android development skills to an employer?

Combine three things: a live session where an Android practitioner watches you build or debug a Compose screen, an adaptive Kotlin assessment, and a connected GitHub repository. Together they show how you work, which a list of apps alone can't.

What Kotlin coroutine concepts should I understand?

Structured concurrency, scopes tied to lifecycles, dispatchers, cancellation and exception handling, plus Flow for streams of state. These come up in Lemma's Kotlin assessment because most real Android bugs around threading trace back to them.

Is Kotlin only useful for Android?

No. Kotlin also runs on the server and across platforms with Kotlin Multiplatform. Lemma's Kotlin skill covers the language itself, so evidence from server-side work counts too. Android-specific skills are reflected in sessions and in mobile development evidence.

How do I move from Java to Kotlin and show it?

Learn null safety, data and sealed classes, and coroutines first, because that is where Java habits show. Then prove it: take Lemma's Kotlin assessment and book a session where a practitioner reviews code you converted. Connect the repository to back it up.

Skills related to Kotlin

Browse the skills directory

Mobile development

Evidence for building mobile apps that work offline, stay fast and survive real devices.

Evidence for mobile development

Swift

Show how you build iOS apps in Swift and SwiftUI, from state to concurrency.

Evidence for Swift

UI/UX design

Show that your interfaces are usable, accessible and consistent, not just attractive.

Evidence for UI/UX design

Start your Kotlin evidence record.

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