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WebAssembly WASM Module Development Skill

Build high-performance WebAssembly modules with WASI 0.3, multi-language support, and production-ready deployments for web, serverless, and AI workloads. WebAssembly (WASM) runs at near-native speeds across web browsers, serverless platforms, and edge computing environments.

by JSONbored·added 2025-10-16·
Claude CodeCodexWindsurfGeminiCursorCLI
HarnessClaude CodeCodexWindsurfGeminiCursorCLI
Level:advancedType:generalVerified:draft
Review first — review before installing

Open the source and read safety notes before installing.

Prerequisites

  • Rust 1.70+ and wasm-pack (recommended)
  • wasm-bindgen 0.2.87+
  • WASI SDK 20+ (for WASI modules)
  • Node.js 18+ for JavaScript integration
  • Emscripten SDK or Rust toolchain (wasm-pack) or AssemblyScript compiler for compiling source code to WebAssembly
  • Modern browser with WebAssembly support (Chrome 57+, Firefox 52+, Safari 11+, Edge 16+) or Node.js 8+ with WASI support for running WebAssembly modules

Schema details

Install type
package
Reading time
6 min
Difficulty score
100
Troubleshooting
Yes
Breaking changes
No
Package metadata
Package verified
Yes
SHA-256
ef8e4038c38a8508ad1afdd7e0152ba4b64babc941ad5deabffb70122e10e75f
Skill and platform metadata
Skill type
general
Skill level
advanced
Verification
draft
Verified at
2025-10-16
Retrieval sources
https://webassembly.org/
Tested platforms
ClaudeCodexOpenClawCursorWindsurfGemini
PlatformSupportInstall path
claude-codeNative.claude/skills/<skill-name>/SKILL.md
codexNative.agents/skills/<skill-name>/SKILL.md
windsurfNative.windsurf/skills/<skill-name>/SKILL.md
geminiNative.gemini/skills/<skill-name>/SKILL.md or .agents/skills/<skill-name>/SKILL.md
cursorAdapter.cursor/rules/<skill-name>.mdc
cliManualAGENTS.md or tool-specific context file
Full copyable content
use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub fn fibonacci(n: u32) -> u64 {
    match n {
        0 => 0,
        1 => 1,
        _ => {
            let mut a = 0u64;
            let mut b = 1u64;
            for _ in 2..=n {
                let temp = a + b;
                a = b;
                b = temp;
            }
            b
        }
    }
}

#[wasm_bindgen]
pub struct Calculator {
    cache: Vec<u64>,
}

#[wasm_bindgen]
impl Calculator {
    #[wasm_bindgen(constructor)]
    pub fn new() -> Calculator {
        Calculator { cache: vec![0, 1] }
    }

    pub fn nth(&mut self, n: usize) -> u64 {
        while self.cache.len() <= n {
            let len = self.cache.len();
            let next = self.cache[len - 1] + self.cache[len - 2];
            self.cache.push(next);
        }
        self.cache[n]
    }
}

About this resource

Build high-performance WebAssembly modules with WASI 0.3, multi-language support, and production-ready deployments for web, serverless, and AI workloads. WebAssembly (WASM) runs at near-native speeds across web browsers, serverless platforms, and edge computing environments. With WASI 0.3 bringing native async support and WebAssembly 2.0 complete as of March 2025, WASM has transitioned from experimental to production-ready for AI workloads, cloud-native applications, and high-performance web apps. Features include Rust/C++/Go compilation to WASM, wasm-bindgen for JavaScript integration, WASI for system calls, Component Model for interoperability, binary size optimization, SIMD support for performance, and multi-runtime compatibility (browser, Node.js, serverless).

Content

WebAssembly Module Development Skill

What This Skill Enables

Claude can build production-ready WebAssembly modules that run at near-native speeds across web browsers, serverless platforms, and edge computing environments. With WASI 0.3 bringing native async support and WebAssembly 2.0 complete as of March 2025, WASM has transitioned from experimental to production-ready for AI workloads, cloud-native applications, and high-performance web apps.

Compatibility

Native

  • Claude Code / Claude: native skill usage via SKILL.md.
  • Codex/OpenAI workflows: compatible with Agent Skills-style SKILL.md content as reusable workflow instructions.

Manual Adaptation

  • Gemini CLI: native skill usage via .gemini/skills/<skill-name>/SKILL.md or .agents/skills/<skill-name>/SKILL.md where supported.
  • Cursor: use the generated .cursor/rules/*.mdc adapter for project rules.
  • OpenClaw and similar agents: use the same skill content as a reusable prompt/workflow file when native skill import is unavailable.

Prerequisites

Required:

  • Claude Pro subscription or Claude Code CLI
  • Rust (recommended) or C++/Go compiler
  • Node.js 18+ for JavaScript integration
  • Basic understanding of systems programming

What Claude handles automatically:

  • Writing Rust/C++ code optimized for WASM
  • Compiling to WebAssembly with proper optimizations
  • Generating JavaScript bindings with wasm-bindgen
  • Setting up WASI for system calls
  • Implementing Component Model for interoperability
  • Optimizing binary size and performance
  • Testing WASM modules in multiple runtimes

How to Use This Skill

Create a Basic WASM Module

Prompt: "Build a WebAssembly module in Rust that calculates Fibonacci numbers. Include JavaScript bindings and deploy to npm."

Claude will:

  1. Set up Rust project with wasm-pack
  2. Write optimized Fibonacci implementation
  3. Add wasm-bindgen annotations
  4. Compile to WASM with size optimizations
  5. Generate TypeScript definitions
  6. Create npm package configuration
  7. Include usage examples for web and Node.js

Image Processing with WASM

Prompt: "Create a WebAssembly module that applies image filters (grayscale, blur, sharpen) to ImageData from canvas. Optimize for processing 4K images in real-time."

Claude will:

  1. Write Rust image processing algorithms
  2. Use rayon for parallel processing
  3. Interface with JavaScript canvas API
  4. Implement zero-copy memory sharing
  5. Add SIMD optimizations where available
  6. Create worker thread wrapper
  7. Benchmark against pure JavaScript

AI Model Inference with WASM

Prompt: "Build a WebAssembly module that runs ONNX neural network models in the browser. Support image classification with MobileNetV3."

Claude will:

  1. Integrate wasm-bindgen with onnxruntime-web
  2. Load and cache ONNX models
  3. Implement preprocessing pipeline
  4. Run inference with WebAssembly backend
  5. Add batching for multiple inputs
  6. Optimize memory allocation
  7. Include model quantization for smaller binaries

Serverless Function with WASI

Prompt: "Create a WebAssembly module with WASI 0.3 that processes CSV files, performs data transformations, and writes results to stdout. Deploy to Fermyon Spin."

Claude will:

  1. Write Rust code using WASI SDK
  2. Implement async file I/O with WASI 0.3
  3. Add CSV parsing and transformation logic
  4. Configure for Spin serverless platform
  5. Set up component model interfaces
  6. Add error handling and logging
  7. Deploy with spin.toml configuration

Tips for Best Results

  1. Choose Rust for Production: While multiple languages compile to WASM, Rust offers the best tooling (wasm-pack, wasm-bindgen) and smallest binary sizes. Ask Claude to use Rust unless you have specific requirements.

  2. Optimize Binary Size: WASM modules should be <500KB for web deployments. Request wasm-opt -Oz optimization and enable LTO (Link-Time Optimization) in Cargo.toml.

  3. Use Component Model: For WASI 0.3, request Component Model implementation for better interoperability and async support.

  4. Memory Management: WebAssembly uses linear memory. Ask Claude to implement proper memory allocation strategies and avoid memory leaks with proper drop implementations.

  5. JavaScript Interop: Use wasm-bindgen for seamless JavaScript integration. Request TypeScript definitions generation for better DX.

  6. SIMD When Available: For compute-intensive tasks, ask Claude to use WebAssembly SIMD instructions for 4-8x performance improvements.

Common Workflows

High-Performance Web App Component

"Create a WebAssembly module for my React app that:
1. Parses and validates 10MB JSON files instantly
2. Performs complex data aggregations
3. Exports results to CSV format
4. Includes TypeScript types
5. Loads asynchronously without blocking UI
6. Caches compiled module in IndexedDB
7. Falls back to JavaScript if WASM not supported"

Cryptocurrency Mining (Educational)

"Build a WebAssembly SHA-256 hasher in Rust:
1. Implements Bitcoin mining algorithm
2. Uses multi-threading with Web Workers
3. Achieves >1000 hashes per second
4. Includes difficulty adjustment
5. Reports progress to JavaScript
6. Optimized with SIMD instructions"

Video Codec in Browser

"Create a WebAssembly H.264 decoder:
1. Decode video streams in real-time (30fps)
2. Output to canvas via ImageData
3. Support seeking and playback controls
4. Use multi-threading for parallel decode
5. Implement memory-efficient frame buffer
6. Package as Web Component"

Database Query Engine

"Build a WebAssembly SQLite query engine:
1. Compile SQLite to WASM with WASI
2. Implement virtual file system in browser
3. Support full SQL query syntax
4. Persist database to IndexedDB
5. Include transaction support
6. Expose async API to JavaScript
7. Add query performance analytics"

Troubleshooting

Issue: WASM module binary is too large (>2MB) Solution: Enable LTO and opt-level in Cargo.toml, run wasm-opt with -Oz flag, remove unused dependencies, and consider dynamic linking for shared code.

Issue: JavaScript can't call WASM functions Solution: Ensure wasm-bindgen attributes are present (#[wasm_bindgen]), rebuild with wasm-pack, and check that JavaScript imports the generated bindings correctly.

Issue: Performance slower than expected Solution: Enable WASM SIMD, use multi-threading with Web Workers, avoid frequent boundary crossings between JS and WASM, and profile with Chrome DevTools Performance tab.

Issue: Memory errors or crashes Solution: Check for buffer overflows, ensure proper memory allocation, implement Drop trait for cleanup, and use wasm-bindgen's #[wasm_bindgen(inspectable)] for debugging.

Issue: WASI functions not available Solution: Update to WASI SDK 0.3+, configure WASI runtime (wasmtime, wasmer), and use preview2 modules. Not all WASI functions are available in browser environments.

Issue: Cannot debug WASM code Solution: Enable source maps with wasm-pack build --dev, use Chrome DevTools WASM debugging, add console.log bindings via web_sys crate, or use wasmtime with --invoke for CLI debugging.

Learn More

Features

  • Near-native performance in browser and serverless environments with optimized WASM binaries
  • Multi-language support: Rust (recommended), C++, Go, AssemblyScript with comprehensive tooling
  • WASI 0.3 with native async support and preview2 modules for system call integration
  • Component Model for interoperability and modular WebAssembly applications
  • wasm-bindgen for seamless JavaScript integration with TypeScript definitions generation
  • Binary size optimization with wasm-opt, LTO, and code size reduction techniques
  • SIMD support for 4-8x performance improvements in compute-intensive tasks
  • Multi-runtime compatibility: browser, Node.js, Wasmtime, Wasmer, WasmEdge, and serverless platforms

Use Cases

  • High-performance web applications with compute-intensive operations (image processing, data parsing)
  • AI model inference in browser with ONNX runtime and neural network execution
  • Serverless functions with portable code using WASI and Fermyon Spin
  • Edge computing workloads with low-latency requirements and resource constraints
  • Database query engines and data processing pipelines in browser environments
  • Video codecs and multimedia processing with real-time performance requirements
Content outline
#webassembly#wasm#rust#performance#wasi

Source citations

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