How to use the WebAssembly Expert agent skill (wasm-expert)

What is an agent skill and what does wasm-expert make the agent do?

An agent skill is a folder containing a SKILL.md file with instructions that an AI agent reads when a request matches the skill's description. The wasm-expert skill is one such file. When it is active, the agent follows its guidance on WebAssembly topics rather than giving a generic answer.

The guidance covers four areas: compiling Rust, C and other languages to WebAssembly; building portable server-side modules that target wasm32-wasi; designing composable components with WIT (WebAssembly Interface Types); and integrating Wasm modules into web applications with attention to startup and binary size. It also flags common pitfalls, such as WASI support varying between runtimes, linear memory that grows but never shrinks, and the need to test on the real target engine.

The file is guidance only. It does not run code itself, and its commands are not checked against current tool versions.

How do you install the wasm-expert skill?

Download the ZIP for the skill from this page. Then choose one of two routes.

For a personal install that applies to all your projects, unzip the download into ~/.claude/skills/. For a single project, unzip it into that project's .claude/skills/ folder. Either way, the wasm-expert folder with its SKILL.md file should sit inside the skills directory.

If you use the Claude apps, you can instead upload the skill under Settings → Capabilities → Skills.

• Personal install: ~/.claude/skills/
• Project install: .claude/skills/ inside your project
• Claude apps: Settings → Capabilities → Skills, then upload

How do you trigger the skill with natural requests?

You do not need a special command. Ask about WebAssembly in plain language and the agent will apply the skill when your request matches its description, which covers WebAssembly, WASI, the component model, Rust or C compilation to Wasm, and browser integration.

Be specific about your goal and your target. Saying that you want a browser build behaves differently from wanting a server-side WASI module, and the skill's guidance separates those cases.

• Compile a Rust crate to Wasm for a browser page.
• Build a command-line tool to wasm32-wasi that reads files.
• Design a WIT interface so a host app can load plugins.
• Reduce the size of my .wasm file for faster page loads.
• Load a Wasm module with streaming instantiation without blocking the page.

What commands does the guidance suggest?

The skill names several commands and tools. These are the ones written in its guidance, which you should verify against your installed tool versions before running them.

• wasm-pack build --target web for browser builds from Rust
• cargo build --target wasm32-wasi for server-side WASI modules
• wasm-bindgen to expose Rust functions to JavaScript (annotate with #[wasm_bindgen])
• wasm-tools compose to link one component's imports to another's exports
• wasm-opt -Oz for size or -O3 for speed
• wasm-tools strip to remove custom sections and debug information
• WebAssembly.instantiateStreaming(fetch("module.wasm"), importObject) in the browser

What do you need before using it?

You need a Rust toolchain plus wasm-pack or cargo for Wasm targets, since the guidance suggests these. Optional tools named in the guidance are wasm-opt, wasm-tools and wasm-bindgen. The skill does not install any of them for you.

The skill runs no scripts and uses no network access, according to its listing. Everything it does happens through the agent's answers and the commands you choose to run.

• Rust toolchain with wasm-pack or cargo
• Optional: wasm-opt, wasm-tools, wasm-bindgen

What are the safety notes?

The skill itself contains no scripts and makes no network calls. The commands it suggests, such as building or optimizing binaries, will run on your machine only if you or the agent execute them, so review any command before approving it.

The guidance also stresses a security model worth keeping in mind: grant a Wasm module only the capabilities it needs through explicit imports. This matters most in plugin systems that run untrusted modules.

What are good tips for getting useful answers?

Name your target (browser or WASI server), your source language, and your runtime, because WASI support differs between Wasmtime, Wasmer and WasmEdge. Ask for a size or startup goal if that matters, since the guidance covers binary size and streaming compilation.

Always test the result on the runtime you will actually ship to. The guidance warns that behavior differs between V8, SpiderMonkey, JavaScriptCore and server runtimes, especially for threading and SIMD.

• State the target: browser or server-side WASI.
• Name the runtime you plan to use.
• Ask for specific trade-offs, such as size versus speed.
• Verify commands against your installed tool versions.