--- title: Build a counter description: Build a counter using Durable Objects and Workers with RPC methods. image: https://developers.cloudflare.com/dev-products-preview.png --- > Documentation Index > Fetch the complete documentation index at: https://developers.cloudflare.com/durable-objects/llms.txt > Use this file to discover all available pages before exploring further. [Skip to content](#%5Ftop) # Build a counter Build a counter using Durable Objects and Workers with RPC methods. This example shows how to build a counter using Durable Objects and Workers with [RPC methods](https://developers.cloudflare.com/workers/runtime-apis/rpc) that can print, increment, and decrement a `name` provided by the URL query string parameter, for example, `?name=A`. * [ JavaScript ](#tab-panel-8657) * [ TypeScript ](#tab-panel-8658) * [ Python ](#tab-panel-8659) JavaScript ``` import { DurableObject } from "cloudflare:workers"; // Workerexport default { async fetch(request, env) { let url = new URL(request.url); let name = url.searchParams.get("name"); if (!name) { return new Response( "Select a Durable Object to contact by using" + " the `name` URL query string parameter, for example, ?name=A", ); } // A stub is a client Object used to send messages to the Durable Object. let stub = env.COUNTERS.getByName(name); // Send a request to the Durable Object using RPC methods, then await its response. let count = null; switch (url.pathname) { case "/increment": count = await stub.increment(); break; case "/decrement": count = await stub.decrement(); break; case "/": // Serves the current value. count = await stub.getCounterValue(); break; default: return new Response("Not found", { status: 404 }); } return new Response(`Durable Object '${name}' count: ${count}`); },}; // Durable Objectexport class Counter extends DurableObject { async getCounterValue() { let value = (await this.ctx.storage.get("value")) || 0; return value; } async increment(amount = 1) { let value = (await this.ctx.storage.get("value")) || 0; value += amount; // You do not have to worry about a concurrent request having modified the value in storage. // "input gates" will automatically protect against unwanted concurrency. // Read-modify-write is safe. await this.ctx.storage.put("value", value); return value; } async decrement(amount = 1) { let value = (await this.ctx.storage.get("value")) || 0; value -= amount; await this.ctx.storage.put("value", value); return value; }} ``` TypeScript ``` import { DurableObject } from "cloudflare:workers"; export interface Env { COUNTERS: DurableObjectNamespace;} // Workerexport default { async fetch(request, env) { let url = new URL(request.url); let name = url.searchParams.get("name"); if (!name) { return new Response( "Select a Durable Object to contact by using" + " the `name` URL query string parameter, for example, ?name=A", ); } // A stub is a client Object used to send messages to the Durable Object. let stub = env.COUNTERS.get(name); let count = null; switch (url.pathname) { case "/increment": count = await stub.increment(); break; case "/decrement": count = await stub.decrement(); break; case "/": // Serves the current value. count = await stub.getCounterValue(); break; default: return new Response("Not found", { status: 404 }); } return new Response(`Durable Object '${name}' count: ${count}`); },} satisfies ExportedHandler; // Durable Objectexport class Counter extends DurableObject { async getCounterValue() { let value = (await this.ctx.storage.get("value")) || 0; return value; } async increment(amount = 1) { let value: number = (await this.ctx.storage.get("value")) || 0; value += amount; // You do not have to worry about a concurrent request having modified the value in storage. // "input gates" will automatically protect against unwanted concurrency. // Read-modify-write is safe. await this.ctx.storage.put("value", value); return value; } async decrement(amount = 1) { let value: number = (await this.ctx.storage.get("value")) || 0; value -= amount; await this.ctx.storage.put("value", value); return value; }} ``` Python ``` from workers import DurableObject, Response, WorkerEntrypointfrom urllib.parse import urlparse, parse_qs # Workerclass Default(WorkerEntrypoint): async def fetch(self, request): parsed_url = urlparse(request.url) query_params = parse_qs(parsed_url.query) name = query_params.get('name', [None])[0] if not name: return Response( "Select a Durable Object to contact by using" + " the `name` URL query string parameter, for example, ?name=A" ) # A stub is a client Object used to send messages to the Durable Object. stub = self.env.COUNTERS.getByName(name) # Send a request to the Durable Object using RPC methods, then await its response. count = None if parsed_url.path == "/increment": count = await stub.increment() elif parsed_url.path == "/decrement": count = await stub.decrement() elif parsed_url.path == "" or parsed_url.path == "/": # Serves the current value. count = await stub.getCounterValue() else: return Response("Not found", status=404) return Response(f"Durable Object '{name}' count: {count}") # Durable Objectclass Counter(DurableObject): def __init__(self, ctx, env): super().__init__(ctx, env) async def getCounterValue(self): value = await self.ctx.storage.get("value") return value if value is not None else 0 async def increment(self, amount=1): value = await self.ctx.storage.get("value") value = (value if value is not None else 0) + amount # You do not have to worry about a concurrent request having modified the value in storage. # "input gates" will automatically protect against unwanted concurrency. # Read-modify-write is safe. await self.ctx.storage.put("value", value) return value async def decrement(self, amount=1): value = await self.ctx.storage.get("value") value = (value if value is not None else 0) - amount await self.ctx.storage.put("value", value) return value ``` Finally, configure your Wrangler file to include a Durable Object [binding](https://developers.cloudflare.com/durable-objects/get-started/#4-configure-durable-object-bindings) and [migration](https://developers.cloudflare.com/durable-objects/reference/durable-objects-migrations/) based on the namespace and class name chosen previously. * [ wrangler.jsonc ](#tab-panel-8660) * [ wrangler.toml ](#tab-panel-8661) JSONC ``` { "$schema": "./node_modules/wrangler/config-schema.json", "name": "my-counter", "main": "src/index.ts", "durable_objects": { "bindings": [ { "name": "COUNTERS", "class_name": "Counter" } ] }, "migrations": [ { "tag": "v1", "new_sqlite_classes": [ "Counter" ] } ]} ``` TOML ``` "$schema" = "./node_modules/wrangler/config-schema.json"name = "my-counter"main = "src/index.ts" [[durable_objects.bindings]]name = "COUNTERS"class_name = "Counter" [[migrations]]tag = "v1"new_sqlite_classes = [ "Counter" ] ``` ### Related resources * [Workers RPC](https://developers.cloudflare.com/workers/runtime-apis/rpc/) * [Durable Objects: Easy, Fast, Correct — Choose three ↗](https://blog.cloudflare.com/durable-objects-easy-fast-correct-choose-three/). ```json {"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/durable-objects/examples/build-a-counter/#page","headline":"Build a counter · Cloudflare Durable Objects docs","description":"Build a counter using Durable Objects and Workers with RPC methods.","url":"https://developers.cloudflare.com/durable-objects/examples/build-a-counter/","inLanguage":"en","image":"https://developers.cloudflare.com/dev-products-preview.png","dateModified":"2026-04-21","publisher":{"@type":"Organization","name":"Cloudflare","url":"https://www.cloudflare.com/"},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"}} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/durable-objects/","name":"Durable Objects"}},{"@type":"ListItem","position":3,"item":{"@id":"/durable-objects/examples/","name":"Examples"}},{"@type":"ListItem","position":4,"item":{"@id":"/durable-objects/examples/build-a-counter/","name":"Build a counter"}}]} ```