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Kotlin/JS

Free#3 of 28 in Code Transpilers

Kotlin/JS: A free Kotlin-to-JavaScript toolchain for browser and Node.js projects. Ranked #3 of 28 in Code Transpilers by our editors (8.8/10); pricing: Free plan; best for kotlin teams targeting browsers or Node.js.

8.8/10Editor score

Visit Kotlin/JS

Kotlin/JS8.8 Visit Kotlin/JS

At a glance

Editor score
8.8 / 10
Pricing
Free plan
Best for
Kotlin teams targeting browsers or Node.js
Free plan
Yes
Paid from
Free
Intermediate output
Yes
Conversion mode
Source-to-source
Founded
2000
Facts checked
22 Sep 2026

Where it wins
- Compiles to ES5 and ES2015 for browser and Node.js targets
- Supports npm packages, webpack, and JavaScript module interoperability
- Generates TypeScript declarations and offers production minification
Where it doesn't
- Requires Kotlin code and compatible dependencies as input
- Projects are configured through the Kotlin Multiplatform Gradle plugin
- Support channels are community resources and documentation

Our verdict on Kotlin/JS

Kotlin/JS is a source-to-source compiler and development toolchain for building browser and Node.js applications with Kotlin. It transpiles Kotlin code, the standard library, and compatible dependencies into JavaScript, with ES5 and ES2015 compilation targets. That makes it a fit for teams that want Kotlin in web or Node.js projects, including solo developers through enterprise teams, while keeping JavaScript as the output language.

The toolchain connects Kotlin projects to the JavaScript ecosystem through npm dependency support, webpack bundling, JavaScript module interoperability, and TypeScript declaration generation. Incremental compilation supports the development workflow; production minification and dead-code elimination address output optimization. Projects are configured with the Kotlin Multiplatform Gradle plugin, so teams already organizing builds around Gradle can use that path. These features suit projects that need to combine Kotlin code with npm packages or expose declarations to TypeScript consumers. Teams looking for a transpiler that accepts languages other than Kotlin should look elsewhere.

Kotlin/JS is free and open source, with no paid tier distinctions in the published product details. Its deployment model is self-hosted, and support channels are community resources and documentation. The trade-off is that a team takes responsibility for its project setup and relies on those support channels rather than a paid support tier. Choose Kotlin/JS when Kotlin is the intended source language and JavaScript ecosystem compatibility matters; consider an alternative if the project depends on a different source language or requires a different support model.

Your product? Our editors can test Kotlin/JS in depth and publish a review, labelled as paid · from $149/mo →

Kotlin/JS pricing

Plans Free planFree Free to use — no paid tier required for the core job.

See plans on kotlinlang.org

Kotlin/JS fact sheet

Free plan	Yes
Paid from	Free
Source languages	Not verified
Target languages	Not verified
Syntax-version conversion	Yes
Intermediate output	Yes
CLI access	Yes
API access	Not verified
Conversion mode	Source-to-source
Deployment	Self-hosted
Platforms	Web, Windows, macOS, Linux
Support	Community, Docs
Built for	Solo, Small business, Mid-market, Enterprise (editorial estimate)
Integrations	6 integrations: Gradle, npm, webpack, Node.js, TypeScript, JavaScript modules
Pricing	Free plan
Website	kotlinlang.org
Facts checked	22 Sep 2026

Kotlin/JS integrations

Kotlin/JS lists 6 integrations on its own site.

Gradle
npm
webpack
Node.js
TypeScript
JavaScript modules

Alternatives to Kotlin/JS

See all Kotlin/JS alternatives →

Kotlin/JS vs the competition

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Featured on iTechGuides

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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

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Last updated 7 Oct 2026 · How we research and update