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WebAssembly Text format (WAT) is the human-readable representation of WebAssembly modules. While WebAssembly normally ships as a compact binary (.wasm), WAT expresses the same instructions using S-expression syntax, letting you read, write, and learn the low-level stack machine by hand. Modules declare functions, memories, globals, imports, and exports, and the format maps directly onto the binary opcodes a Wasm engine executes.
CompileBytes assembles WAT corresponding to the WebAssembly 1.0 (MVP) specification. WAT is typically converted to the binary format with tools like wat2wasm from the WebAssembly Binary Toolkit (WABT), then instantiated by a runtime. Working in WAT is useful for understanding how compilers target Wasm, debugging generated output, and exploring core concepts like linear memory, typed values, and the structured control flow that make WebAssembly portable and safe.
main.wat is the entry point for each run.
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(module
(func $add (param $a i32) (param $b i32) (result i32)
local.get $a
local.get $b
i32.add)
(export "add" (func $add)))(module
(func (export "answer") (result i32)
i32.const 42))(module
(func (export "sumTo") (param $n i32) (result i32)
(local $i i32)
(local $total i32)
(block $done
(loop $cont
(br_if $done (i32.gt_s (local.get $i) (local.get $n)))
(local.set $total
(i32.add (local.get $total) (local.get $i)))
(local.set $i (i32.add (local.get $i) (i32.const 1)))
(br $cont)))
local.get $total))(module
(memory (export "mem") 1)
(global $counter (mut i32) (i32.const 0))
(func (export "bump") (result i32)
(global.set $counter
(i32.add (global.get $counter) (i32.const 1)))
global.get $counter))(module
(func (export "max") (param $a i32) (param $b i32) (result i32)
(if (result i32) (i32.gt_s (local.get $a) (local.get $b))
(then (local.get $a))
(else (local.get $b)))))(module
(func $fac (export "fac") (param $n i32) (result i32)
(if (result i32) (i32.le_s (local.get $n) (i32.const 1))
(then (i32.const 1))
(else
(i32.mul
(local.get $n)
(call $fac (i32.sub (local.get $n) (i32.const 1))))))))(module
(func (export "average") (param $a f64) (param $b f64) (result f64)
(f64.div
(f64.add (local.get $a) (local.get $b))
(f64.const 2))))(module
(memory (export "mem") 1)
(func (export "roundTrip") (result i32)
(i32.store (i32.const 0) (i32.const 99))
(i32.load (i32.const 0))))(module
(func (export "abs") (param $x i32) (result i32)
(select
(i32.sub (i32.const 0) (local.get $x))
(local.get $x)
(i32.lt_s (local.get $x) (i32.const 0)))))The editor uses Monaco, the engine behind VS Code, with language-aware editing tools and familiar keyboard controls.
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WASM (WAT) is one of 46 single-file compiler scratchpads. Each run submits only main.wat; local sibling-file imports are not enabled.
Linked-project languages (23): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Bun, Objective-C.
Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme.
Download file exports the active WASM (WAT) source file.