stackblitz-common-errors

name	stackblitz-common-errors
description	Fix WebContainer and StackBlitz errors: COOP/COEP, SharedArrayBuffer, boot failures. Use when WebContainers fail to boot, embeds don't load, or processes crash inside WebContainers. Trigger: "stackblitz error", "webcontainer error", "SharedArrayBuffer not defined".
allowed-tools	Read, Grep, Bash(curl:*)
version	1.5.0
license	MIT
author	Jeremy Longshore <[e-mail]>
tags	["saas","ide","webcontainers","stackblitz"]
compatibility	Designed for Claude Code

StackBlitz Common Errors

Error Reference

SharedArrayBuffer is not defined

Cause: Missing cross-origin isolation headers.

Cross-Origin-Embedder-Policy: require-corp
Cross-Origin-Opener-Policy: same-origin

Fix: Add both headers to your server. In Vite: server.headers config.

Failed to boot WebContainer

Cause: Only one WebContainer instance allowed per page.

// BAD: Multiple boot calls
const wc1 = await WebContainer.boot();
const wc2 = await WebContainer.boot(); // Fails!

// GOOD: Singleton pattern
let instance: WebContainer | null = null;
async function getWC() {
  if (!instance) instance = await WebContainer.boot();
  return instance;
}

npm install hangs or fails

Cause: Large dependency tree or network issue in WebContainer.

// Use --prefer-offline and minimal deps
const proc = await wc.spawn('npm', ['install', '--prefer-offline']);
const code = await proc.exit;
if (code !== 0) {
  .();
   retry =  wc.(, []);
   retry.;
}