workers-multi-lang

Multi-language Workers development with Rust, Python, and WebAssembly. Use when building Workers in languages other than JavaScript/TypeScript, or when integrating WASM modules for performance-critical code.

Install with Tessl CLI

npx tessl i github:secondsky/claude-skills --skill workers-multi-lang

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Review — 88%

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SKILL.md

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Multi-Language Workers Development

Build Cloudflare Workers using Rust, Python, or WebAssembly for performance-critical operations.

Language Comparison

Feature	JavaScript/TS	Rust	Python
Startup	Fast	Fastest (WASM)	Moderate
CPU Perf	Good	Excellent	Good
Memory	Higher	Lower	Higher
Bundle Size	Smaller	Medium	Larger
Type Safety	Optional (TS)	Strict	Optional
Best For	General apps	CPU-intensive	Data/ML

Quick Decision

Need maximum performance? → Rust/WASM
Heavy computation (crypto, image processing)? → Rust/WASM
Data processing, ML inference? → Python
General web apps? → JavaScript/TypeScript

Top 10 Multi-Lang Errors

Error	Language	Cause	Solution
`WebAssembly.instantiate() failed`	Rust	Invalid WASM	Check wasm-pack build output
`Module parse failed: Unexpected token`	Rust	ESM/CJS mismatch	Use `--target bundler`
`Cannot find module`	Python	Missing dep	Add to pyproject.toml
`Out of memory`	All	Large WASM	Enable streaming instantiation
`Exceeded CPU time limit`	All	Long computation	Chunk processing
`wasm-bindgen version mismatch`	Rust	Dep conflict	Align versions in Cargo.toml
`RuntimeError: unreachable`	Rust	Panic in WASM	Add proper error handling
`TypeError: not a function`	Rust	Missing export	Add `#[wasm_bindgen]` attribute
`Python worker startup timeout`	Python	Slow init	Minimize imports
`SharedArrayBuffer not supported`	All	Security	Add COOP/COEP headers

Rust Quick Start

# Install tools
cargo install wasm-pack

# Create project
cargo new --lib my-worker
cd my-worker

# Add to Cargo.toml
cat >> Cargo.toml << 'EOF'
[lib]
crate-type = ["cdylib"]

[dependencies]
wasm-bindgen = "0.2"
worker = "0.3"
console_error_panic_hook = "0.1"

[profile.release]
opt-level = "s"
lto = true
EOF

// src/lib.rs
use worker::*;

#[event(fetch)]
async fn fetch(req: Request, env: Env, _ctx: Context) -> Result<Response> {
    console_error_panic_hook::set_once();

    Router::new()
        .get("/", |_, _| Response::ok("Hello from Rust!"))
        .get("/compute", |_, _| {
            // CPU-intensive computation
            let result = heavy_computation();
            Response::ok(format!("Result: {}", result))
        })
        .run(req, env)
        .await
}

fn heavy_computation() -> u64 {
    (1..1_000_000).filter(|n| is_prime(*n)).count() as u64
}

fn is_prime(n: u64) -> bool {
    if n < 2 { return false; }
    (2..=(n as f64).sqrt() as u64).all(|i| n % i != 0)
}

Python Quick Start (Workers for Platforms)

# pyproject.toml
[project]
name = "my-worker"
version = "0.1.0"
requires-python = ">=3.12"
dependencies = []

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

# src/entry.py
from js import Response, Headers

async def on_fetch(request, env):
    url = request.url

    if "/compute" in url:
        result = heavy_computation()
        return Response.new(f"Result: {result}")

    return Response.new("Hello from Python!")

def heavy_computation():
    """CPU-intensive computation"""
    return sum(1 for n in range(2, 100000) if is_prime(n))

def is_prime(n):
    if n < 2:
        return False
    return all(n % i != 0 for i in range(2, int(n**0.5) + 1))

WASM Module Integration

// Load and use WASM module in TypeScript Worker
import wasmModule from './pkg/my_lib_bg.wasm';
import { init, process_data } from './pkg/my_lib';

let wasmInstance: WebAssembly.Instance;

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    // Initialize WASM once
    if (!wasmInstance) {
      wasmInstance = await WebAssembly.instantiate(wasmModule);
      init();
    }

    // Use WASM function
    const result = process_data(inputData);

    return Response.json({ result });
  },
};

When to Load References

Reference	Load When
`references/rust-workers.md`	Building Workers with Rust/WASM
`references/python-workers.md`	Using Python on Workers for Platforms
`references/wasm-integration.md`	Integrating WASM modules in any Worker

Performance Tips

WASM Initialization: Cache instance, use streaming
Memory: Use typed arrays for data transfer
Bundle Size: Enable LTO, strip debug info
Cold Starts: Keep WASM modules small
Data Transfer: Minimize JS/WASM boundary crossings