#374

Global Rank · of 600 Skills

durable-objects AI Agent Skill

View Source: cloudflare/skills

Safe

Installation

npx skills add cloudflare/skills --skill durable-objects

5.3K

Installs

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Your knowledge of Durable Objects APIs and configuration may be outdated.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

// wrangler.jsonc
{
  "durable_objects": {
    "bindings": [{ "name": "MY_DO", "class_name": "MyDurableObject" }]
  },
  "migrations": [{ "tag": "v1", "new_sqlite_classes": ["MyDurableObject"] }]
}

Basic Durable Object Pattern

import { 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 DO
  2. Use getByName() for deterministic routing - Same input = same DO instance
  3. Use SQLite storage - Configure new_sqlite_classes in migrations
  4. Initialize in constructor - Use blockConcurrencyWhile() for schema setup only
  5. Use RPC methods - Not fetch() handler (compatibility date >= 2024-04-03)
  6. Persist first, cache second - Always write to storage before updating in-memory state
  7. 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

// Deterministic - preferred for most cases
const stub = env.MY_DO.getByName("room-123");

// From existing ID string
const id = env.MY_DO.idFromString(storedIdString);
const stub = env.MY_DO.get(id);

// New unique ID - store mapping externally
const id = env.MY_DO.newUniqueId();
const stub = env.MY_DO.get(id);

Storage Operations

// 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

// Schedule (replaces existing)
await this.ctx.storage.setAlarm(Date.now() + 60_000);

// Handler
async alarm(): Promise<void> {
  // Process scheduled work
  // Optionally reschedule: await this.ctx.storage.setAlarm(...)
}

// Cancel
await this.ctx.storage.deleteAlarm();

Testing Quick Start

import { 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);
  });
});

Installs

Installs 5.3K
Global Rank #374 of 600

Security Audit

ath Safe
socket Safe
Alerts: 0 Score: 90
snyk Low
zeroleaks Safe
Score: 93
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How to use this skill

1

Install durable-objects by running npx skills add cloudflare/skills --skill durable-objects in your project directory. Run the install command above in your project directory. The skill file will be downloaded from GitHub and placed in your project.

2

No configuration needed. Your AI agent (Claude Code, Cursor, Windsurf, etc.) automatically detects installed skills and uses them as context when generating code.

3

The skill enhances your agent's understanding of durable-objects, helping it follow established patterns, avoid common mistakes, and produce production-ready output.

What you get

Skills are plain-text instruction files — not executable code. They encode expert knowledge about frameworks, languages, or tools that your AI agent reads to improve its output. This means zero runtime overhead, no dependency conflicts, and full transparency: you can read and review every instruction before installing.

Compatibility

This skill works with any AI coding agent that supports the skills.sh format, including Claude Code (Anthropic), Cursor, Windsurf, Cline, Aider, and other tools that read project-level context files. Skills are framework-agnostic at the transport level — the content inside determines which language or framework it applies to.

Data sourced from the skills.sh registry and GitHub. Install counts and security audits are updated regularly.

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