Kotlin
Kotlin is a general purpose, free, open-source, statically typed “pragmatic” programming language initially designed for the JVM (Java Virtual Machine) and Android that combines object-oriented and functional programming features.
What detecting Kotlin tells you about a site
Kotlin on a website is almost always server-side (Kotlin compiles to JVM bytecode and shares Java's deployment story), so the tells overlap with Java — a `JSESSIONID` cookie, a Spring/Ktor `Server` signature — with Ktor's distinctive headers as the clearest Kotlin-specific marker. Detecting it flags a JVM team that chose the modern, more concise language over Java, which often signals a newer service or a team that has modernised its backend tooling.
The detail that matters for Kotlin
The hard part is separating Kotlin from Java: both compile to the same JVM bytecode and share the `JSESSIONID`/servlet signatures, so a Spring Boot app could be written in either. A `Ktor` server header is the one clearly Kotlin-specific tell. Absent that, read a JVM signature as 'JVM, possibly Kotlin' rather than a confirmed Kotlin detection.
Kotlin in a real-world stack
When you find Kotlin, it rarely travels alone. Ktor or Spring Boot on the server; the JVM ecosystem (Gradle builds, JVM libraries) around it.
About
Kotlin is a general purpose, free, open-source, statically typed “pragmatic” programming language initially designed for the JVM (Java Virtual Machine) and Android that combines object-oriented and functional programming features.
Categories: Programming languages
Quick facts
Detection methodology for Programming languages
Programming languages reveal themselves through extension fingerprints (`.php` URLs for PHP, `.aspx` for ASP.NET), framework-specific patterns and (for client-side runtime languages like TypeScript and Sass) the `node_modules/<lang>/package.json` entry inside the sourcemap. Bun, Node.js and Deno on the server side identify themselves via response headers when emitted (`X-Powered-By: Bun`, `X-Bun-Version`).
FAQ
How do I check if a website is using Kotlin?
Open the page in Chrome, click the Sourcemap Explorer toolbar icon, and read the Stack tab. Kotlin's fingerprints span response headers, asset URL prefixes, runtime globals and sourcemap paths, and the popup flags Kotlin whenever any combination of them is found. The same checks can be reproduced manually in DevTools — see the "How we detect" section above.
What Kotlin version can Sourcemap Explorer detect?
Kotlin ships as a hosted programming languages rather than a bundled npm package, so version-specific detection isn't always possible. Where the platform leaks a version in response headers (`X-Powered-By`, `Server`, generator meta tags) we surface it; otherwise we report presence only.
Is Kotlin open source?
Yes, Kotlin is open source. The license details are listed on the official site (https://kotlinlang.org), and the codebase typically lives on a public source-control host.
Where can I read more about Kotlin?
Official site: https://kotlinlang.org. For Sourcemap Explorer's detection guide, see the deep-dive link below or the related guides in the cross-link section.
Keep reading on Sourcemap Explorer
Practical guides
Alternative tools
Detected by Sourcemap Explorer
Open the popup on any page running Kotlinand you'll see the exact version pulled from the bundled package.json when sourcemaps are exposed.