Learn WAT with Real Code Examples

WAT provides a low-level, readable, LISP-like syntax for WebAssembly modules.

It directly maps to the binary WebAssembly format, instruction-by-instruction.

Used primarily for debugging, hand-crafted Wasm, education, and minimal runtime experimentation.

Supports fine-grained control over Wasm memory, functions, imports, exports, and types.

Typically compiled into Wasm using wat2wasm tools or integrated toolchains.

Module definitions using `(module ...)`

Functions with explicit param/returns

Linear memory definition and access

Imports and exports

Instructions for control flow, arithmetic, memory, tables

Stack machine - operations push/pop values

Linear memory - explicit memory access

S-expressions - LISP-like syntax

Instructions - Wasm opcodes in text form

Module structure - imports, exports, functions, types

module.wat - main Wasm text module

module.wasm - compiled binary

index.js - loader/interop script

tests/ - validate Wasm output

examples/ - sample WAT modules

Write .wat module

Compile using wat2wasm

Inspect binary via wasm2wat

Load in browser or Node.js

Call exported functions from JS

Beginner: simple add function

Intermediate: memory access + loops

Advanced: tables, imports & exports

Expert: manual stack manipulation + complex control flow

Auditor: analyze binary from wasm2wat

WAT vs Wasm Binary: WAT is readable; binary is compact and executable

WAT vs Rust-Wasm: WAT is manual; Rust generates Wasm automatically

WAT vs AssemblyScript: WAT is low-level; AS is high-level TS-like

WAT vs C/C++-Wasm: WAT is hand-crafted; C compiles high-level code

WAT vs Go/TinyGo: WAT avoids runtimes entirely

2015 - WebAssembly concept announced

2017 - WebAssembly MVP in browsers

2018 - WAT standardized as text format

2022 - WAT gains support for GC, reference types

2024–2025 - Memory64, tail calls, component model support

WAT - WebAssembly Text Format

S-expression - LISP-like syntax

Stack machine - push/pop architecture

WASI - WebAssembly System Interface

Opcode - low-level instruction