Compilers: ids, versions and commands

C#, F# and Visual Basic moved from .NET 9 to .NET 10 in October 2026. The old ids dotnet-csharp-9, dotnet-fsharp-9 and dotnet-vbnet-9 still work and run on .NET 10; new code should send the -10 ids above.

How Each Language Is Compiled

Your code is saved as code plus the language's extension, then run with these commands. Compilation counts toward the 30-second timeout; time measures the run command and total includes it.

• C# is compiled by csc with the settings of a .NET 10 console project in Release mode: C# 14, optimized, no implicit usings, nullable warnings off. The regex source generator ([GeneratedRegex]) works; the code-analysis (CA) warnings and the interop and JSON source generators are not loaded, which keeps compiles fast.
• Java runs in single-file source mode: the file is compiled in memory and its first top-level class runs, with no separate javac step.
• Rust builds are optimized but keep overflow checks, so integer overflow panics as it would in a debug build.
• Haskell is compiled without optimization flags.
• TypeScript runs on Deno without type checking, so untyped JavaScript runs too. Reads are limited to its workspace and temporary files: read stdin with Deno.stdin or fs.readFileSync(0), since Deno refuses /dev/stdin. Remote package downloads are unavailable; network access is off for every language.
• JavaScript runs on Node.js 24 LTS, where CommonJS (require) and ES modules (import, top-level await) both work. A file can't mix require with top-level await; Node then can't tell which module format it is.
• SQL runs in the SQLite 3 shell on a fresh in-memory database, with code as its script; it stops at the first error. input isn't read as SQL: the script reads it with readfile('input').
• Visual Basic is compiled by vbc with the settings of a .NET 10 console project in Release mode (Option Strict off, Option Infer on), without the CA analyzers, as C# is.
• Kotlin is compiled by kotlinc into a jar that includes the Kotlin standard library, then run on Java 25 with the same JVM settings as Java.
• Swift keeps its runtime checks under -O. A failed check, such as an index out of range, exits with code 132 and a crash report on stderr that points at the line.
• COBOL is compiled in free format. For fixed-format code, make >>SOURCE FORMAT IS FIXED the first line.
• Assembly is 64-bit NASM for Linux. A program that defines a global main is linked by gcc -no-pie instead of ld, so it can call the C library. 32-bit system calls (int 0x80) crash; use syscall.
• Octave runs the file as a script, so it can't start with function (put 1; first), and functions must be defined before they're called.
• Julia's memory includes its system image and loaded libraries, so it often reports the full 512 MB; programs can hold about 300 MB of data.
• Erlang runs as an escript would: execution starts at main/1, the -module and -export lines are optional, and compiler warnings go to stderr. An uncaught exception exits with code 127.
• Prolog is SWI-Prolog. A program runs from an :- initialization(main). directive, as on GNU Prolog, and ends when it finishes or calls halt. An error, or a main that fails, makes the exit code 1.
• Scala is compiled by scalac into classes, then the program's one entry point runs: an @main method or an object with def main(args: Array[String]): Unit.
• Common Lisp runs as an SBCL script with a 384 MB heap; Groovy and Clojure compile and run in one Java 25 process with a 320 MB heap.
• FreeBASIC has no graphics library, so programs that use Screen fail to link.
• Zig builds in Debug mode, so safety checks stay on and a panic prints a stack trace that points at the line. Zig 0.17's I/O is new: main takes init: std.process.Init, and stdin and stdout are read and written through init.io, as the editor's example shows.
• Nim builds in its default debug mode, with runtime checks on, so an unhandled exception prints a traceback with the line.
• A Crystal run takes about 8 seconds, most of it compiling in LLVM, so even a short program takes that long.
• An Ada file can hold several units in any order. gnatchop splits it into one file per unit, and the main program is the last procedure outside a package. Errors and exceptions still give the line in your file, such as code.adb:7. Ada 2022 syntax is on.
• PowerShell's Read-Host reads the next line of input without echoing it to stdout, as PowerShell's own does when input is redirected. Other prompts, such as a missing mandatory parameter, fail instead of waiting.
• A Racket program starts with a #lang line. Minimal Racket is installed, plus #lang scheme, #lang r5rs, data/ and math/.
• Objective-C compiles with Clang against GNUstep's Foundation and modern runtime, so @autoreleasepool, literals, subscripting, synthesized properties and blocks work. ARC is off, so code that calls retain and release compiles too; __weak works either way. There's no AppKit or UIKit.

How Long a Run Takes

Seconds from request to response for a small program that echoes its input, through the sync endpoint, measured on production on 18 October 2026: 20 runs per language, one at a time, from our own network, so add your round trip to api.onlinecompiler.io. Each run starts a fresh sandbox and compiles the code; your own programs add the time they take to run.