Keyboard shortcuts

Press ← or → to navigate between chapters

Press S or / to search in the book

Press ? to show this help

Press Esc to hide this help

wasmz logo

Introduction

wasmz is a WebAssembly runtime written in Zig, designed to be fast, compact, and easy to embed. It implements a full-featured interpreter with support for modern WebAssembly proposals.

Real-World Testing

wasmz passes real-world WebAssembly module tests:

  • esbuild - JavaScript bundler compiled to WASM
  • QuickJS - Lightweight JavaScript engine compiled to WASM
  • SQLite - Database engine compiled to WASM

These integration tests validate wasmz’s compatibility with production WASM workloads.

WebAssembly Support

wasmz supports all current WebAssembly proposals.

  • MVP - All core instructions and validation rules
  • Multi-value - Functions and blocks with multiple return values
  • Bulk operations - Memory and table bulk operations
  • Sign-extension - Sign-extension instructions
  • GC - Structs, arrays, and reference types with automatic memory management
  • SIMD - 128-bit vector operations
  • Exception Handling - Both legacy and new proposal formats
  • Threading - Shared memory and atomic operations

WASI Support

WASI Preview 1 - Full implementation

  • File system operations (fd_read, fd_write, path_open, etc.)
  • Socket operations (sock_accept, sock_recv, sock_send, etc.)
  • Environment variables and arguments
  • Random number generation
  • Process control (proc_exit, proc_raise)
  • Clock and time operations
  • Polling (poll_oneoff)

Embedding

  • Zig API - Native Zig interface with full type safety
  • C API - Minimal C ABI for embedding in any language
  • CLI tool - Standalone command-line runner

Project Structure

wasmz/
├── src/
│   ├── root.zig          # Public API entry point
│   ├── main.zig          # CLI implementation
│   ├── capi.zig          # C API implementation
│   ├── core/             # Core data types
│   ├── parser/           # WASM binary parser
│   ├── compiler/         # Stack-to-register compiler
│   ├── engine/           # Execution engine
│   ├── vm/               # Virtual machine
│   ├── wasmz/            # High-level API
│   └── wasi/             # WASI implementation
├── include/
│   └── wasmz.h           # C API header
├── tests/                # Integration tests
└── docs/                 # Documentation

Dependencies

wasmz has minimal dependencies:

  • zigrc: Reference counting implementation (inlined in src/libs/)
  • libc: Only for the C API

No external libraries or system dependencies are required for the core runtime.

Zig Version

wasmz requires Zig 0.15.2 or compatible version.

License

MIT License - see LICENSE file for details.