Run WebAssembly online

Run WebAssembly (WAT) online — text format, real runtime.

Version

Firecracker microVM live per-test verdicts multi-file compile

WebAssembly is the portable binary instruction set for a stack machine — originally for browsers, now for edge compute, server workloads, and plugin systems. The text format (WAT) is human-readable.

Starter code

What you get in WebAssembly

Clicking "Run now" opens the playground with this exact code and a matching test case pre-loaded — passes on first Run.

webassembly

WebAssembly 1

(module
  (import "wasi_snapshot_preview1" "fd_write"
    (func $fd_write (param i32 i32 i32 i32) (result i32)))
  (memory 1)
  (export "memory" (memory 0))
  (data (i32.const 8) "Hello, World!\n")
  (func $main (export "_start")
    (i32.store (i32.const 0) (i32.const 8))
    (i32.store (i32.const 4) (i32.const 14))
    (drop (call $fd_write (i32.const 1) (i32.const 0) (i32.const 1) (i32.const 20)))
  )
)

stdin →(empty)

expected →

Hello, World!

FAQ

Common questions about WebAssembly on ls-judge

Text or binary?: Both — WAT compiled with wat2wasm, or paste a base64 .wasm.
WASI?: The runtime supports the WASI preview 1 syscalls for stdio.
Free?: Yes.
Entry export?: _start (WASI convention).