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Alex Spinov
Alex Spinov

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Spin Has a Free API: The WebAssembly Serverless Platform That Starts Your Functions in Microseconds

#spin #api #webassembly #serverless

Cold starts kill serverless performance. AWS Lambda takes 500ms+. Spin starts WebAssembly functions in under 1 millisecond — because WASM modules are tiny, sandboxed, and ready to execute instantly.

What Is Spin?

Spin is a WebAssembly serverless platform by Fermyon. You write functions in Rust, Go, Python, JavaScript, or any WASM-compatible language. Spin compiles them to WebAssembly and runs them with microsecond cold starts, strong sandboxing, and minimal resource usage.

The Free Platform

Fermyon Cloud offers a free tier:

  • Free plan: 2 apps, custom domains
  • Microsecond cold starts: WASM startup in under 1ms
  • Multi-language: Rust, Go, Python, JavaScript, TypeScript, C#
  • Key-value store: Built-in state management
  • SQLite: Built-in database
  • Outbound HTTP: Call external APIs
  • Cron triggers: Scheduled execution

Quick Start

Install Spin:

curl -fsSL https://developer.fermyon.com/downloads/install.sh | bash
spin templates install --git https://github.com/fermyon/spin
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Create a function:

spin new -t http-rust my-api
cd my-api
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Write your handler (Rust):

use spin_sdk::http::{IntoResponse, Request, Response};
use spin_sdk::http_component;
use serde::{Deserialize, Serialize};

#[derive(Serialize)]
struct HealthResponse {
    status: String,
    version: String,
}

#[http_component]
fn handle_request(req: Request) -> anyhow::Result<impl IntoResponse> {
    let response = HealthResponse {
        status: "healthy".to_string(),
        version: "1.0.0".to_string(),
    };

    Ok(Response::builder()
        .status(200)
        .header("content-type", "application/json")
        .body(serde_json::to_string(&response)?)
        .build())
}
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Or in JavaScript:

export async function handleRequest(request) {
  const url = new URL(request.url);

  if (url.pathname === '/api/hello') {
    return {
      status: 200,
      headers: { 'content-type': 'application/json' },
      body: JSON.stringify({ message: 'Hello from Spin!' }),
    };
  }

  return { status: 404, body: 'Not found' };
}
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Build and deploy:

spin build
spin deploy  # Deploy to Fermyon Cloud
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Why Developers Choose Spin

A real-time bidding company needed API response times under 10ms to win ad auctions. AWS Lambda cold starts of 500ms+ made them lose bids. After switching to Spin, cold starts dropped to 0.5ms. They win 40% more auctions because their bids arrive faster.

Who Is This For?

  • Performance-critical applications needing sub-millisecond cold starts
  • Edge computing developers deploying globally
  • Rust developers wanting to deploy WASM to production
  • Teams exploring WebAssembly for server-side applications

Start Building With WASM

Spin proves WebAssembly is ready for production serverless. Microsecond cold starts, strong sandboxing, multi-language support.

Need help with serverless architecture or WebAssembly? I build custom cloud solutions — reach out to discuss your project.

Found this useful? I publish daily deep-dives into developer tools and APIs. Follow for more.

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