Online Scala Compiler

Scala combines object-oriented and functional programming on the JVM, with strong static typing driven by a Hindley–Milner-flavored type inference. It compiles to the same bytecode as Java, so it interoperates seamlessly with the entire Java ecosystem — every Java library is a Scala library.

Installing sbt + a JDK + an IDE-aware editor is a ten-minute affair for the first build, then thirty-second increments thereafter. A browser sandbox is faster for one-off expressions, learning FP concepts (immutable data, pattern matching, for-comprehensions), or testing a snippet before pasting it into a build.

Data pipelines (Spark), backend services (Akka HTTP, http4s, Play Framework), functional libraries (Cats, ZIO), REPL-driven development, and gradual migrations from Java codebases. The sandbox runs Scala with JVM tooling.

Paste a snippet — @main def hello(): Unit = println("hi") — hit Run, see stdout. The highlighter recognises Scala idioms: pattern matching with case, for-comprehensions with yield, the Option/Some/None pattern, and implicit conversions.

An online Scala compiler compiles real JVM bytecode from your browser, so case classes, pattern matching and implicit resolution behave exactly as they would inside an sbt project — no build file, no dependency resolution, no waiting on a first sbt compile. Paste a snippet and the output panel shows stdout, or a genuine compiler error, within seconds; sessions autosave and every run gets a link you can hand to a teammate instead of pasting a stack trace into chat. It's a reasonable stand-in for a free Scala interpreter when you're testing a for-comprehension or an Option chain, and just as useful if you haven't installed anything yet and want to run Scala code in the browser first.

Since Scala and Java share a runtime, the Online Java Compiler is worth keeping open for interop checks, and the Online Kotlin Compiler covers the other popular JVM language if you're comparing syntax.

sbt resolving its own dependencies on a clean machine can take longer than the code you wanted to test, which makes it a poor fit for a quick question about how a match expression or a higher-kinded type behaves. Here you can run Scala code in the browser instead: paste the snippet, press Run or Ctrl+Enter, and read actual compiler output below, including real type errors rather than a guess at what the signature means. It's the faster path for working through an immutable-collection pipeline or trying Scala 3's @main syntax for the first time.

Comparing functional style across the JVM and beyond? The Online Haskell Compiler runs on the same editor, and the rest of the catalogue is on the Online Compiler hub.

A first sbt build downloads the Scala compiler, the standard library, and whatever plugins your build.sbt references — easily a few hundred megabytes before a single test runs. This free online Scala compiler skips that entirely: paste code, run it, read the output, move on. The local setup still wins once you're managing a multi-module build or running the Spark or Akka stack for real, but for checking whether a pattern match is exhaustive, the sandbox is faster by minutes.

The Online Haskell Compiler is a natural companion for comparing functional idioms, and the full language list lives on the free online compiler hub.