Dynamic Worker Runner

Run untrusted JavaScript as an ES module Worker using the Worker Loader API. Loaded workers run with globalOutbound: null so they cannot make network requests.

API ReferenceCopy Anchor Link

POST /runCopy Anchor Link

Execute a Worker module string and return its HTTP response status and body.

code string (required)

Full ES module that exports default { fetch }. Max length 10,000 characters.

Example RequestCopy Anchor Link

curl -X POST "https://your-worker.workers.dev/run" \
  -H "Content-Type: application/json" \
  -d '{"code":"export default { async fetch() { return Response.json({ hello: \"world\" }); } }"}'

Success ResponseCopy Anchor Link

{
  "status": 200,
  "body": { "hello": "world" }
}

Error CodesCopy Anchor Link

• 400 - Missing, empty, or too-long code (INVALID_CODE)
• 502 - Loader or isolate failure (RUN_ERROR)

Use CasesCopy Anchor Link

• Learn Dynamic Workers / Worker Loader patterns safely
• Sandbox plugin or customer code without outbound network
• Prototype multi-tenant execution before Workers for Platforms
• Teach isolate isolation and globalOutbound restrictions

LimitationsCopy Anchor Link

• Code must be a complete ES module with default { fetch }
• Max code length 10,000 characters
• No outbound network from the loaded worker
• Dynamic Workers / Worker Loader may require account entitlements

DeploymentCopy Anchor Link

curl -X POST "https://your-worker.workers.dev/run" \
  -H "Content-Type: application/json" \
  -d '{"code":"export default { async fetch() { return Response.json({ ok: true }); } }"}'

Local DevelopmentCopy Anchor Link

cd apps/experiments/dynamic-worker-runner
npm install
npm run dev

curl -X POST "http://localhost:8787/run" \
  -H "Content-Type: application/json" \
  -d '{"code":"export default { async fetch() { return Response.json({ hello: \"world\" }); } }"}'

ConfigurationCopy Anchor Link

wrangler.json declares:

• Worker Loader binding LOADER

Cloudflare Features UsedCopy Anchor Link

• Workers - Edge compute runtime
• Dynamic Workers / Worker Loaders - Load and run module code at request time