Durable Objects

CloudflareOfficialPublished by Cloudflare

Skill
Tool integration
Cloud and DevOps
Apache-2.0
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From the author

Build, debug, or review Cloudflare Durable Objects code for persistent state and coordination.

— the description by Cloudflare

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides guidance on implementing Cloudflare Durable Objects, which enable stateful coordination on the edge. It covers the use of Durable Objects for tasks requiring strong consistency, persistent connections, and per-entity storage. The skill includes best practices for configuration, storage operations using SQLite or KV, alarm scheduling, and testing strategies, while emphasizing the importance of using current documentation for API implementation.

What it does

Provides patterns for creating and configuring Durable Object classes.
Offers guidance on using SQLite and KV storage within Durable Objects.
Assists in setting up alarms for scheduled per-entity work.
Helps with configuring bindings and migrations in wrangler files.
Supports the implementation of RPC methods and WebSocket handlers.
Provides references for testing Durable Objects using Vitest.

When to use it

When building stateful coordination features like chat rooms or multiplayer games.
When implementing systems requiring strong consistency, such as inventory management.
When managing per-user data or multi-tenant application state.
When handling persistent connections like WebSockets.
When reviewing existing Durable Object code for alignment with best practices.

Advantages

Promotes the use of current, authoritative documentation via retrieval.
Provides clear patterns for deterministic routing and storage initialization.
Helps avoid common anti-patterns like blocking concurrency on every request.
Supports structured configuration for migrations and bindings.

Usage examples

“How do I initialize a SQLite database in a Durable Object?”: The agent provides a pattern using blockConcurrencyWhile in the constructor to execute SQL schema creation.
“What is the best way to route requests to a specific Durable Object instance?”: The agent explains how to use getByName for deterministic routing to ensure the same input maps to the same object instance.
“How should I handle scheduled tasks within a Durable Object?”: The agent demonstrates the use of setAlarm and the alarm() handler method for per-object scheduled work.
“Can you review my Durable Object migration configuration?”: The agent checks the wrangler configuration against the provided patterns for bindings and new_sqlite_classes.

Install

Download the skill as a ZIP:
https://autogineer.com/agent-skills/cloudflare/durable-objects/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip durable-objects.zip -d .agents/skills

Documentation by Cloudflare

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/index.md
API Reference	https://developers.cloudflare.com/durable-objects/api/index.md
Best Practices	https://developers.cloudflare.com/durable-objects/best-practices/index.md
Examples	https://developers.cloudflare.com/durable-objects/examples/index.md
Roles and permissions	https://developers.cloudflare.com/workers/authorization/durable-objects/index.md

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’s Vitest integration
Designing sharding strategies and parent-child relationships

Reference Documentation

./references/rules.md - Core rules, storage, concurrency, RPC, alarms
Testing reference - Current Vitest documentation, migration choices, and test selection
Workers reference - Workers handlers, types, configuration, tracing, and local debugging

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

Model around coordination atoms - One DO per chat room/game/user, not one global DO
Use getByName() for deterministic routing - Same input = same DO instance
Use SQLite storage - Configure new_sqlite_classes in migrations
Initialize in constructor - Use blockConcurrencyWhile() for schema setup only
Use RPC methods - Not fetch() handler (compatibility date >= 2024-04-03)
Persist first, cache second - Always write to storage before updating in-memory state
One alarm per DO - setAlarm() replaces any existing alarm

Authorization

Durable Objects do not have separate roles or permissions; access follows the Worker that implements them. Retrieve the current Durable Objects authorization guidance before granting observability or Data Studio access, and scope the Workers role to the intended Worker or Workers product.

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

Read the testing reference before configuring a suite or writing Durable Object tests. It routes to current setup, APIs, and examples and identifies the behavior to cover.

Skill feedback

If the user reports that this skill gave incorrect or outdated guidance, or is missing information, read references/skill-feedback.md.

Files

ATTRIBUTION.mdAdded by AutoGineer866 B
LICENSELicence file added by AutoGineer11.1 KiB
SKILL.md6.1 KiB
references/rules.md2.8 KiB
references/skill-feedback.md2.7 KiB
references/testing.md2.5 KiB
references/workers.md7.8 KiB

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Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Published by

Cloudflare

Publisher

Cloudflare (Official)

Source

cloudflare/skills · skills/durable-objects · commit 6eb6c78

Licence

Apache License 2.0 (redistribution allowed)

LICENSE (added by AutoGineer from LICENSE)
ATTRIBUTION.md (written by AutoGineer)

Synced

2026-11-09

AutoGineer is not affiliated with or endorsed by Cloudflare or Cloudflare.

Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download durable-objects.zip

From the author

AutoGineer summary

What it does

When to use it

Advantages

Usage examples

Install

Documentation by Cloudflare

Durable Objects

Retrieval Sources

When to Use

Reference Documentation

Core Principles

Use Durable Objects For

Do NOT Use For

Quick Reference

Wrangler Configuration

Basic Durable Object Pattern

Critical Rules

Authorization

Anti-Patterns (NEVER)

Stub Creation

Storage Operations

Alarms

Testing

Skill feedback

Files

LICENSE

Requirements and compatibility

Security

Attribution and licence

Related skills

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