PaperclipOrg
Claude Agent Skill · by Cloudflare

Durable Objects

A solid implementation guide for Cloudflare Durable Objects that actually gets the patterns right. Covers the full lifecycle from wrangler configuration and SQL

Install
Terminal · npx
$npx skills add https://github.com/cloudflare/skills --skill durable-objects
Works with Paperclip

How Durable Objects fits into a Paperclip company.

Durable Objects drops into any Paperclip agent that handles this kind of work. Assign it to a specialist inside a pre-configured PaperclipOrg company and the skill becomes available on every heartbeat — no prompt engineering, no tool wiring.

S
SaaS FactoryPaired

Pre-configured AI company — 18 agents, 18 skills, one-time purchase.

$27$59
Explore pack
Source file
SKILL.md186 lines
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---name: durable-objectsdescription: Create and review Cloudflare Durable Objects. Use when building stateful coordination (chat rooms, multiplayer games, booking systems), implementing RPC methods, SQLite storage, alarms, WebSockets, or reviewing DO code for best practices. Covers Workers integration, wrangler config, and testing with Vitest. Biases towards retrieval from Cloudflare docs over pre-trained knowledge.--- # Durable Objects Build stateful, coordinated applications on Cloudflare's edge using Durable Objects. ## Retrieval Sources Your knowledge of Durable Objects APIs and configuration may be outdated. **Prefer retrieval over pre-training** for any Durable Objects task. | Resource | URL ||----------|-----|| Docs | https://developers.cloudflare.com/durable-objects/ || API Reference | https://developers.cloudflare.com/durable-objects/api/ || Best Practices | https://developers.cloudflare.com/durable-objects/best-practices/ || Examples | https://developers.cloudflare.com/durable-objects/examples/ | Fetch the relevant doc page when implementing features. ## When to Use - Creating new Durable Object classes for stateful coordination- Implementing RPC methods, alarms, or WebSocket handlers- Reviewing existing DO code for best practices- Configuring wrangler.jsonc/toml for DO bindings and migrations- Writing tests with `@cloudflare/vitest-pool-workers`- Designing sharding strategies and parent-child relationships ## Reference Documentation - `./references/rules.md` - Core rules, storage, concurrency, RPC, alarms- `./references/testing.md` - Vitest setup, unit/integration tests, alarm testing- `./references/workers.md` - Workers handlers, types, wrangler config, observability Search: `blockConcurrencyWhile`, `idFromName`, `getByName`, `setAlarm`, `sql.exec` ## Core Principles ### Use Durable Objects For | Need | Example ||------|---------|| Coordination | Chat rooms, multiplayer games, collaborative docs || Strong consistency | Inventory, booking systems, turn-based games || Per-entity storage | Multi-tenant SaaS, per-user data || Persistent connections | WebSockets, real-time notifications || Scheduled work per entity | Subscription renewals, game timeouts | ### Do NOT Use For - Stateless request handling (use plain Workers)- Maximum global distribution needs- High fan-out independent requests ## Quick Reference ### Wrangler Configuration ```jsonc// wrangler.jsonc{  "durable_objects": {    "bindings": [{ "name": "MY_DO", "class_name": "MyDurableObject" }]  },  "migrations": [{ "tag": "v1", "new_sqlite_classes": ["MyDurableObject"] }]}``` ### Basic Durable Object Pattern ```typescriptimport { DurableObject } from "cloudflare:workers"; export interface Env {  MY_DO: DurableObjectNamespace<MyDurableObject>;} export class MyDurableObject extends DurableObject<Env> {  constructor(ctx: DurableObjectState, env: Env) {    super(ctx, env);    ctx.blockConcurrencyWhile(async () => {      this.ctx.storage.sql.exec(`        CREATE TABLE IF NOT EXISTS items (          id INTEGER PRIMARY KEY AUTOINCREMENT,          data TEXT NOT NULL        )      `);    });  }   async addItem(data: string): Promise<number> {    const result = this.ctx.storage.sql.exec<{ id: number }>(      "INSERT INTO items (data) VALUES (?) RETURNING id",      data    );    return result.one().id;  }} export default {  async fetch(request: Request, env: Env): Promise<Response> {    const stub = env.MY_DO.getByName("my-instance");    const id = await stub.addItem("hello");    return Response.json({ id });  },};``` ## Critical Rules 1. **Model around coordination atoms** - One DO per chat room/game/user, not one global DO2. **Use `getByName()` for deterministic routing** - Same input = same DO instance3. **Use SQLite storage** - Configure `new_sqlite_classes` in migrations4. **Initialize in constructor** - Use `blockConcurrencyWhile()` for schema setup only5. **Use RPC methods** - Not fetch() handler (compatibility date >= 2024-04-03)6. **Persist first, cache second** - Always write to storage before updating in-memory state7. **One alarm per DO** - `setAlarm()` replaces any existing alarm ## Anti-Patterns (NEVER) - Single global DO handling all requests (bottleneck)- Using `blockConcurrencyWhile()` on every request (kills throughput)- Storing critical state only in memory (lost on eviction/crash)- Using `await` between related storage writes (breaks atomicity)- Holding `blockConcurrencyWhile()` across `fetch()` or external I/O ## Stub Creation ```typescript// Deterministic - preferred for most casesconst stub = env.MY_DO.getByName("room-123"); // From existing ID stringconst id = env.MY_DO.idFromString(storedIdString);const stub = env.MY_DO.get(id); // New unique ID - store mapping externallyconst id = env.MY_DO.newUniqueId();const stub = env.MY_DO.get(id);``` ## Storage Operations ```typescript// SQL (synchronous, recommended)this.ctx.storage.sql.exec("INSERT INTO t (c) VALUES (?)", value);const rows = this.ctx.storage.sql.exec<Row>("SELECT * FROM t").toArray(); // KV (async)await this.ctx.storage.put("key", value);const val = await this.ctx.storage.get<Type>("key");``` ## Alarms ```typescript// Schedule (replaces existing)await this.ctx.storage.setAlarm(Date.now() + 60_000); // Handlerasync alarm(): Promise<void> {  // Process scheduled work  // Optionally reschedule: await this.ctx.storage.setAlarm(...)} // Cancelawait this.ctx.storage.deleteAlarm();``` ## Testing Quick Start ```typescriptimport { env } from "cloudflare:test";import { describe, it, expect } from "vitest"; describe("MyDO", () => {  it("should work", async () => {    const stub = env.MY_DO.getByName("test");    const result = await stub.addItem("test");    expect(result).toBe(1);  });});```