| name | webassembly-component-development |
| description | Comprehensive guide to WebAssembly component development covering WASI fundamentals, component composition patterns, language interoperability, runtime compatibility, and troubleshooting. Use this skill when building WebAssembly components, writing or editing WIT (WebAssembly Interface Types) definitions, composing components with wac or wasm-tools, targeting wasip1/wasip2/wasip3, working with `.wit` or `.wasm` files, or whenever the user mentions WASI, the component model, wkg, wstd, or component composition. |
| license | Apache-2.0 |
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
