WebAssembly Component Development

This skill provides comprehensive expertise in developing WebAssembly components, including WASI fundamentals, composition patterns, runtime compatibility, and troubleshooting.

Key Defaults

• Build: Use wash build when the project has .wash/config.yaml. Use wash build --skip-fetch for plugins (since wasmcloud:wash interface isn't published). Otherwise cargo build --target wasm32-wasip2 --release.
• Target: wasm32-wasip2 (Rust 1.82+ tier-2 target). WASI 0.2 (wasip2) is the current standard.
• Async: Pick one — tokio 1.50+ with RUSTFLAGS="--cfg tokio_unstable", or wstd (lighter, Wasm-native). Do not mix.
• Strings: Always UTF-8 on wasip2. Avoid as_encoded_bytes().
• Threading: Unsupported. Design single-threaded. Avoid rayon, threaded tokio, std::thread::spawn.
• wasmCloud docs: Always use https://wasmcloud.com/docs/ — never /docs/v1/.

Reference Files

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Summary

• Component Model enables language-agnostic, composable WebAssembly applications
• WASI 0.2 (wasip2) is the current standard with full networking and UTF-8 guarantees
• Design coarse-grained interfaces for better performance
• Test in target runtime early and often
• Use wash build for wasmCloud projects — handles compatibility automatically
• Document runtime requirements and maintain compatibility matrices