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Bindings (env)

Bindings allow your Worker to interact with resources on the Cloudflare Developer Platform.

The following bindings available today:

  • AI: Run generative AI inference and machine learning models on GPUs, without managing servers or infrastructure.
  • Analytics Engine: Write high-cardinality data and metrics at scale, directly from Workers.
  • Browser Rendering: Programmatically control and interact with a headless browser instance.
  • D1: APIs available in Cloudflare Workers to interact with D1. D1 is Cloudflare’s native serverless database.
  • Dispatcher (Workers for Platforms): Let your customers deploy their own code to your platform, and dynamically dispatch requests from your Worker to their Worker.
  • Durable Objects: A globally distributed coordination API with strongly consistent storage.
  • Environment Variables: Add string and JSON values to your Worker.
  • Hyperdrive: Connect to your existing database from Workers, turning your existing regional database into a globally distributed database.
  • KV: Global, low-latency, key-value data storage.
  • mTLS: Configure your Worker to present a client certificate to services that enforce an mTLS connection.
  • Queues: Send and receive messages with guaranteed delivery.
  • R2: APIs available in Cloudflare Workers to read from and write to R2 buckets. R2 is S3-compatible, zero egress-fee, globally distributed object storage.
  • Rate Limiting: Define rate limits and interact with them directly from your Cloudflare Worker
  • Secrets: Add encrypted secrets to your Worker.
  • Service bindings: Facilitate Worker-to-Worker communication.
  • Vectorize: APIs available in Cloudflare Workers to interact with Vectorize. Vectorize is Cloudflare’s globally distributed vector database.
  • Version metadata: Exposes Worker version metadata (versionID and versionTag). These fields can be added to events emitted from the Worker to send to downstream observability systems.

​​ What is a binding?

When you declare a binding on your Worker, you grant it a specific capability, such as being able to read and write files to an R2 bucket. For example:

main = "./src/index.js"
r2_buckets = [
{ binding = "MY_BUCKET", bucket_name = "<MY_BUCKET_NAME>" }
export default {
async fetch(request, env) {
const key = url.pathname.slice(1);
await env.MY_BUCKET.put(key, request.body);
return new Response(`Put ${key} successfully!`);

You can think of a binding as a permission and an API in one piece. With bindings, you never have to add secret keys or tokens to your Worker in order to access resources on your Cloudflare account — the permission is embedded within the API itself. The underlying secret is never exposed to your Worker’s code, and therefore can’t be accidentally leaked.