openai-cloudflare-deploy/references/workerd/README.md
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Workerd Runtime
V8-based JS/Wasm runtime powering Cloudflare Workers. Use as app server, dev tool, or HTTP proxy.
⚠️ IMPORTANT SECURITY NOTICE
workerd is NOT a hardened sandbox. Do not run untrusted code. It's designed for deploying YOUR code locally/self-hosted, not multi-tenant SaaS. Cloudflare production adds security layers not present in open-source workerd.
Decision Tree: When to Use What
95% of users: Use Wrangler
- Local development: wrangler dev (uses workerd internally)
- Deployment: wrangler deploy (deploys to Cloudflare)
- Types: wrangler types (generates TypeScript types)
Use raw workerd directly only if: - Self-hosting Workers runtime in production - Embedding runtime in C++ application - Custom tooling/testing infrastructure - Debugging workerd-specific behavior
Never use workerd for: - Running untrusted/user-submitted code - Multi-tenant isolation (not hardened) - Production without additional security layers
Key Features
- Standards-based: Fetch API, Web Crypto, Streams, WebSocket
- Nanoservices: Service bindings with local call performance
- Capability security: Explicit bindings prevent SSRF
- Backwards compatible: Version = max compat date supported
Architecture
Config (workerd.capnp)
├── Services (workers/endpoints)
├── Sockets (HTTP/HTTPS listeners)
└── Extensions (global capabilities)
Quick Start
workerd serve config.capnp
workerd compile config.capnp myConfig -o binary
workerd test config.capnp
Platform Support & Beta Status
| Platform | Status | Notes |
|---|---|---|
| Linux (x64) | Stable | Primary platform |
| macOS (x64/ARM) | Stable | Full support |
| Windows | Beta | Use WSL2 for best results |
| Linux (ARM64) | Experimental | Limited testing |
workerd is in active development. Breaking changes possible. Pin versions in production.
Core Concepts
- Service: Named endpoint (worker/network/disk/external)
- Binding: Capability-based resource access (KV/DO/R2/services)
- Compatibility date: Feature gate (always set!)
- Modules: ES modules (recommended) or service worker syntax
Reading Order (Progressive Disclosure)
Start here: 1. This README (overview, decision tree) 2. patterns.md - Common workflows, framework examples
When you need details: 3. configuration.md - Config format, services, bindings 4. api.md - Runtime APIs, TypeScript types 5. gotchas.md - Common errors, debugging