name = "my-worker"
main = "src/index.ts"
compatibility_date = "2024-01-01"
[vars]
ENVIRONMENT = "production"
[[kv_namespaces]]
binding = "MY_KV"
id = "abc123"
[[d1_databases]]
binding = "DB"
database_name = "my-db"
database_id = "def456"
[[r2_buckets]]
binding = "BUCKET"
bucket_name = "my-bucket"

Worker Basics

interface Env {
  MY_KV: KVNamespace; DB: D1Database; BUCKET: R2Bucket;
  ENVIRONMENT: string; API_KEY: string;
}

export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    const url = new URL(request.url);
    if (url.pathname === "/api/health") return Response.json({ status: "ok" });
    if (request.method === "POST" && url.pathname === "/api/data") {
      const body = await request.json();
      return new Response("Created", { status: 201 });
    }
    return new Response("Not Found", { status: 404 });
  },
};

Wrangler CLI

wrangler dev                    # local dev server on localhost:8787
wrangler dev --remote           # dev against real Cloudflare infrastructure
wrangler deploy                 # deploy to production
wrangler tail                   # stream live logs from deployed worker
wrangler secret put API_KEY     # set an encrypted secret
wrangler secret list            # list configured secrets
wrangler delete                 # remove the deployed worker

Routing

Manual routing with a map, or use hono/itty-router for path params:

// Manual
const routes: Record<string, () => Promise<Response>> = {
  "/api/users": () => handleUsers(request),
  "/api/posts": () => handlePosts(request),
};
const handler = routes[new URL(request.url).pathname];
if (handler) return handler();

// Hono (recommended for complex routing)
import { Hono } from "hono";
const app = new Hono<{ Bindings: Env }>();
app.get("/users/:id", (c) => c.json({ id: c.req.param("id") }));
export default app;

KV Store

Global, low-latency key-value store. Eventually consistent. Best for read-heavy data.

wrangler kv namespace create MY_KV
wrangler kv namespace create MY_KV --preview

await env.MY_KV.put("user:123", JSON.stringify({ name: "Alice" }), {
  expirationTtl: 3600, metadata: { created: Date.now() },
});
const value = await env.MY_KV.get("user:123", "json");
const list = await env.MY_KV.list({ prefix: "user:", limit: 100 });
await env.MY_KV.delete("user:123");

D1 Database

SQLite at the edge with queries, transactions, and migrations.

wrangler d1 create my-db
wrangler d1 execute my-db --command "CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)"
wrangler d1 migrations create my-db init
wrangler d1 migrations apply my-db

const { results } = await env.DB.prepare("SELECT * FROM users WHERE id = ?").bind(userId).all();
await env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind("Alice").run();
await env.DB.batch([
  env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind("Bob"),
  env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind("Carol"),
]);
const user = await env.DB.prepare("SELECT * FROM users WHERE id = ?").bind(1).first();

R2 Storage

S3-compatible object storage with no egress fees.

wrangler r2 bucket create my-bucket

// Upload
await env.BUCKET.put("images/photo.jpg", imageData, {
  httpMetadata: { contentType: "image/jpeg" },
});
// Download
const object = await env.BUCKET.get("images/photo.jpg");
if (object) {
  return new Response(object.body, {
    headers: { "Content-Type": object.httpMetadata?.contentType ?? "application/octet-stream" },
  });
}
// List, delete
const listed = await env.BUCKET.list({ prefix: "images/", limit: 50 });
await env.BUCKET.delete("images/photo.jpg");

For large files use createMultipartUpload(), uploadPart(), complete().

Durable Objects

Strongly consistent, stateful compute. Each object has a unique ID and private storage. Use for rate limiters, WebSocket coordination, collaborative editing, session state.

[[durable_objects.bindings]]
name = "COUNTER"
class_name = "Counter"
[[migrations]]
tag = "v1"
new_classes = ["Counter"]

export class Counter implements DurableObject {
  constructor(private state: DurableObjectState, private env: Env) {}
  async fetch(request: Request): Promise<Response> {
    const current = (await this.state.storage.get<number>("count")) ?? 0;
    await this.state.storage.put("count", current + 1);
    return Response.json({ count: current + 1 });
  }
}
// Calling from a worker:
const id = env.COUNTER.idFromName("my-counter");
const response = await env.COUNTER.get(id).fetch(request);

Workers AI

Run ML models at the edge. Add [ai] with binding = "AI" to wrangler.toml.

// Text generation
const resp = await env.AI.run("@cf/meta/llama-3.1-8b-instruct", {
  messages: [{ role: "user", content: "Summarize this article." }],
});
// Embeddings
const emb = await env.AI.run("@cf/baai/bge-base-en-v1.5", { text: ["document to embed"] });
// Image classification
const cls = await env.AI.run("@cf/microsoft/resnet-50", { image: await request.arrayBuffer() });

Environment Variables and Secrets

Non-sensitive values go in wrangler.toml under [vars]. Set secrets with wrangler secret put API_KEY. Both accessed through env.API_KEY, env.ENVIRONMENT, etc.

Multiple environments:

[env.staging]
name = "my-worker-staging"
vars = { ENVIRONMENT = "staging" }
[env.production]
name = "my-worker-production"
vars = { ENVIRONMENT = "production" }

Deploy with wrangler deploy --env staging or --env production.

Cron Triggers

[triggers]
crons = ["0 */6 * * *", "30 8 * * 1"]

export default {
  async scheduled(event: ScheduledEvent, env: Env, ctx: ExecutionContext): Promise<void> {
    ctx.waitUntil(doCleanup(env));
  },
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    return new Response("OK");
  },
};

Test locally: curl "http://localhost:8787/__scheduled?cron=0+*/6+*+*+*"

Middleware Patterns

CORS

function corsHeaders(origin: string): HeadersInit {
  return {
    "Access-Control-Allow-Origin": origin,
    "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS",
    "Access-Control-Allow-Headers": "Content-Type, Authorization",
  };
}

Auth

async function requireAuth(request: Request, env: Env): Promise<Response | null> {
  const token = request.headers.get("Authorization")?.replace("Bearer ", "");
  if (!token || token !== env.API_KEY) {
    return Response.json({ error: "Unauthorized" }, { status: 401 });
  }
  return null; // proceed
}

Rate Limiting

Use a Durable Object to track request timestamps per key. Store timestamps in storage, filter to the current window, reject if over limit, append and persist otherwise.

Local Development

wrangler dev                     # local server with miniflare runtime
wrangler dev --persist-to=./data # persist KV/D1/R2 data locally
wrangler dev --port 3000         # custom port
wrangler dev --remote            # proxy to Cloudflare (real bindings)

Miniflare simulates KV, D1, R2, Durable Objects, and caches locally.

Deployment

wrangler deploy                      # deploy to production
wrangler deploy --env staging        # named environment
wrangler deploy --dry-run            # validate without deploying
wrangler versions list               # list deployed versions
wrangler rollback                    # rollback to previous version

Custom domains:

routes = [{ pattern = "api.example.com/*", zone_name = "example.com" }]

Common Patterns

API Proxy

async function proxyRequest(request: Request, env: Env): Promise<Response> {
  const url = new URL(request.url);
  url.hostname = "api.upstream.com";
  return fetch(new Request(url.toString(), {
    method: request.method,
    headers: { ...Object.fromEntries(request.headers), "X-API-Key": env.UPSTREAM_KEY },
    body: request.body,
  }));
}

Edge Cache

async function cachedFetch(request: Request, ctx: ExecutionContext): Promise<Response> {
  const cache = caches.default;
  let response = await cache.match(request);
  if (response) return response;
  response = await fetch("https://api.origin.com" + new URL(request.url).pathname);
  const cached = new Response(response.body, response);
  cached.headers.set("Cache-Control", "s-maxage=300");
  ctx.waitUntil(cache.put(request, cached.clone()));
  return cached;
}

Webhook Handler

async function handleWebhook(request: Request, env: Env): Promise<Response> {
  const signature = request.headers.get("X-Signature-256") ?? "";
  const body = await request.text();
  const key = await crypto.subtle.importKey(
    "raw", new TextEncoder().encode(env.WEBHOOK_SECRET),
    { name: "HMAC", hash: "SHA-256" }, false, ["verify"]
  );
  const valid = await crypto.subtle.verify(
    "HMAC", key, hexToBytes(signature.replace("sha256=", "")),
    new TextEncoder().encode(body)
  );
  if (!valid) return new Response("Invalid signature", { status: 401 });
  return new Response("OK", { status: 200 });
}

URL Shortener

app.post("/shorten", async (c) => {
  const { url } = await c.req.json();
  const id = crypto.randomUUID().slice(0, 8);
  await c.env.MY_KV.put(`url:${id}`, url, { expirationTtl: 86400 * 30 });
  return c.json({ short: `${new URL(c.req.url).origin}/${id}` });
});
app.get("/:id", async (c) => {
  const target = await c.env.MY_KV.get(`url:${c.req.param("id")}`);
  if (!target) return c.text("Not found", 404);
  return c.redirect(target, 302);
});

Limits

Resource	Free	Paid
CPU time/request	10 ms	30 s (Unbound) / 50 ms
Memory	128 MB	128 MB
Worker size	1 MB	10 MB
Subrequests (fetch)	50	1000
KV reads/day	100K	10M+
KV writes/day	1K	1M+
D1 rows read/day	5M	50B
D1 rows written/day	100K	50M
R2 Class A ops/month	1M	$4.50/M
R2 storage	10 GB	$0.015/GB-mo
Cron triggers	3	3+
Request body size	100 MB	100 MB

Key constraints: no raw TCP/UDP sockets (use WebSockets or Tunnels). crypto.subtle available. Node.js built-ins partially supported via nodejs_compat flag. Globals persist within an isolate but not across cold starts. ctx.waitUntil() extends execution after response for background work.

cloudflare-workers

Cloudflare Workers

Setup

wrangler.toml