WAT Text Format

WebAssembly Text Format (WAT) is the human-readable text representation of WebAssembly binary format. Understanding WAT helps you deeply understand how WASM works.

Why Learn WAT?

• Debugging — Read compiled WASM output
• Learning — Deeply understand WASM semantics
• Optimization — Write efficient low-level code
• Testing — Verify binary output

Basic Syntax

Module Structure

(module
  ;; Comments with ;;
  (func $name ...)
  (memory ...)
  (table ...)
  (global ...))

Functions

Basic Functions

;; Function that returns 42
(module
  (func (export "answer") (result i32)
    (i32.const 42)))

Functions with Parameters

(module
  (func (export "add") (param $a i32) (param $b i32) (result i32)
    local.get $a
    local.get $b
    i32.add))

Stack Machine

WASM is a stack machine — instructions operate on a stack:

;; Add two numbers
(i32.const 5)     ;; Push 5
(i32.const 3)     ;; Push 3
(i32.add)         ;; Pop 3 and 5, push 8

Instruction Reference

Constants

(i32.const 42)     ;; Push i32 constant
(i64.const 9223372036854775807)  ;; Push i64
(f32.const 3.14)   ;; Push f32
(f64.const 2.718281828)  ;; Push f64

Local Variables

(local.get $x)      ;; Push local variable
(local.set $x)      ;; Pop and store to local variable
(local.tee $x)       ;; Duplicate top of stack, then store

Tools

WAT to WASM

# Install wabt (WebAssembly Binary Toolkit)
# macOS
brew install wabt
# Linux
sudo apt install wabt

# WAT to WASM
wat2wasm input.wat -o output.wasm

# WASM to WAT
wasm2wat input.wasm -o output.wat

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