Build a counter

Build a counter using Durable Objects and Workers with RPC methods.

Last updated Oct 12, 2026 This example shows how to build a counter using Durable Objects and Workers with RPC methods that can print, increment, and decrement a name provided by the URL query string parameter, for example, ?name=A.

import { DurableObject } from "cloudflare:workers";

// Worker
export 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 Object
export 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;
    }
}

import { DurableObject } from "cloudflare:workers";

export interface Env {
    COUNTERS: DurableObjectNamespace<Counter>;
}

// Worker
export 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<Env>;

// Durable Object
export 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;
    }
}

from workers import DurableObject, Response, WorkerEntrypoint
from urllib.parse import urlparse, parse_qs

# Worker
class 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 Object
class 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 and migration based on the namespace and class name chosen previously.

{
    "$schema": "./node_modules/wrangler/config-schema.json",
    "name": "my-counter",
    "main": "src/index.ts",
    "upload_source_maps": true,
    "durable_objects": {
        "bindings": [
            {
                "name": "COUNTERS",
                "class_name": "Counter"
            }
        ]
    },
    "migrations": [
        {
            "tag": "v1",
            "new_sqlite_classes": [
                "Counter"
            ]
        }
    ]
}

"$schema" = "./node_modules/wrangler/config-schema.json"
name = "my-counter"
main = "src/index.ts"
upload_source_maps = true

[[durable_objects.bindings]]
name = "COUNTERS"
class_name = "Counter"

[[migrations]]
tag = "v1"
new_sqlite_classes = [ "Counter" ]

Related resources

• Workers RPC
• Durable Objects: Easy, Fast, Correct — Choose three ↗︎.

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description: Create a Durable Object that stores the last location it was accessed from in-memory. title: Durable Object in-memory state image: https://developers.cloudflare.com/durable-objects/examples/durable-object-in-memory-state/og.png?v=8e15bc935b81b2ab

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