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

Load the relevant file when working on the matching topic:

| Topic | File | |-------|------| | Component Model fundamentals, benefits, WASI (wasip2) basics | core-concepts.md | | Composition patterns (simple dependency, adapter, middleware, facade), boundary design, building with wash build / cargo, wac, .wash/config.yaml | composition-and-building.md | | Cross-language composition, supported languages (Rust, Python, JS/TS, Go, C/C++, C#), data type / performance / error handling considerations | language-interop.md | | WASI gotchas (no threading, UTF-8 string assumptions, network capabilities), unknown-import errors, runtime-specific compatibility (wasmtime flags, wasmCloud), version alignment strategies | gotchas-and-runtime.md | | Async with tokio on wasip2, wstd (Wasm-native async stdlib), when to choose which | async.md | | Testing (host harness, mocks, wash integration, feature flags, env setup), debugging workflow, common error patterns, wasm-tools/wash inspect, performance (minimize cross-component calls, streaming, batching) | testing-debugging-performance.md | | Documentation links, development/component-design/runtime-compat best practices, CI/CD examples, common architecture patterns (microservices, plugin, data pipeline) | patterns-and-best-practices.md |

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