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.

Performance

In my benchmarks, wasmz is currently the fastest WebAssembly interpreter I have tested. You can view the full benchmark report here: https://ray-d-song.github.io/wasmz/bench.html.

The benchmark chapter also includes notes on the parser and interpreter optimizations used in wasmz.

If you find workloads where wasmz has a clear disadvantage, please let me know. I will do my best to optimize them :)

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

License

MIT License - see LICENSE file for details.